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A Glossary of Diving Terms

Slang and Jargon used by Rescue Swimmers and Underwater Divers

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Professional Association of
Diving Instructors

Technical Diving International

National Association for Cave

Sub-Aqua Association

International Association of
Nitrox and Technical Divers

Confederation Mondiale des
Activites Subaquatiques

Handicapped Scuba Association

PADI Advanced Open Water Diver

National Association of
Underwater Instructors

Scuba Diving International

Scuba Schools International

British Sub-Aqua Club

Association of Nitrox Divers

PADI Divemaster

Diving Terms

a Glossary of Slang and Jargon
used by Rescue Swimmers and Underwater Divers

Reference Notes

aback :
toward the back, to the rear. Also, when the wind presses against the front or forward part of the sail or sails. Also, to surprise or disconcert; as to be taken aback.

abaft :
behind or to the rear; toward the stern; astern or aft.

abeam :
on a line at right angles to a ship's keel; at right angles to the fore-and-aft line.

abbreviation for Adjustable Buoyancy LifeJacket, the old horsecollar style.

a strong lightweight plastic that's a copolymer of acrylonitrile, butadiene, and styrene, hence its designation by UniRoyal; this plastic core is often sandwiched between vinyl layers to protect it from being degraded by ultraviolet light.

absolute pressure :
the total pressure at any depth, which is a sum of atmospheric pressure and hydrostatic pressure; calculated from a vacuum being rated as the zero point.

absolute temperature scale :
temperature measured on a scale in which the hypothetical lowest limit of physical temperatures is assigned the value of zero (ab∆solute ze∆ro), as in the kelvin and rankine scales; also called absolute temperature or absolute scale. [nb: the degree intervals of the kelvin scale are the same as celsius, as the rankine are the same as fahrenheit]

absolute zero :
the hypothetical temperature at which all molecular activity and kinetic energy ceases; computed at -273.16°C or -459.69°F, and represented as 0°K and 0°R. [nb: the degree intervals of the kelvin scale are the same as celsius, as the rankine are the same as fahrenheit]

abbreviation for Actual Bottom Time; also called bottom time.

abyssal :
pertaining to the biogeographic zone of the ocean bottom between the bathyal and hadal zones; from depths of approximately 13,000 to 21,000 feet. Also, like an abyss, being immeasurable or unfathomable.

accommodation ladder :
a portable flight of steps suspended from the side of a vessel to give crew and/or passenger ingress and egress access from smaller boats alongside; also known as boarding ladder.

acetal resin :
a lightweight polymer (ie: polyoxymethylene) engineered for use as a high-performance metal replacement, exhibiting both high strength and impact resistance; commercially marketed as Delrin, Celcon, Hostaform, Duracon, Kepital, Iupital, and Ultraform.

acre-foot :
a unit of measure for the volume of liquid covered by a surface area sized one acre to a depth of one foot, or equal to 43,56 cubic feet or 325,850 US gallons; it's used in the United States as a reference for large-scale water resources, such as reservoirs, aqueducts, canals, river flows, and the like.

actual bottom time :
the total amount of time a diver spends descending or at depth; calculated to begin upon descent and ends upon starting the ascent; also called bottom time.

abbreviation for American Canadian Underwater Certifications, being Canada's scuba certification body.

abbreviation for an Air-Cushion Vehicle or Air-Cushioned Vehicle; also known as a hovercraft.

adjusted no-decompression limit :
the maximum bottom time for repetitive dives, being equal to the no-decompression limit plus residual nitrogen time.

admeasure :
to measure the dimensions and capacity of a vessel, as for official registration; as derived from apportion.

adrift :
anything unsecured, or that has slipped its mooring or fast, as being out of control, including items improperly stowed, or things lost overboard.

advection :
the horizontal flow of air, water, or the like, which often entails a change of temperature or humidity; as distinct from convection.

aeroembolism :
an obstruction of the circulatory system caused by one or more air bubbles; a condition of decompression sickness.

afoul :
to be or become entangled, or in a state of collision; as to run, come, or fall afoul.

aft :
at the rear or stern, or toward the back of a vessel or craft.

acronym for Arterial Gas Embolism; also called air embolism.

ahoy :
call used by seafarers to hail or alert others; derived "hoy", as to hoist.

air :
a gas mixture present in the earth's atmosphere that's necessary for human respiration, containing 21% oxygen, 78% nitrogen, and 1% other gases (mainly argon) which is compressed into air tanks for recreational scuba diving.

air bladder / bladder :
the inner air cell of a buoyancy compensator (BC), which holds the necessary amount of air used to provide proper neutral buoyancy at depth.

air cell :
a term used to describe a wing-style buoyancy compensator.

air compressor :
a machine that's used to transfer pressurized air into tanks for scuba diving; the air is compressed from the atmospheric level (14.7 psi at sea level) to the capacity of the tank, usually between 2500-3000 psi. [nb: according to the first law of thermodynamics, the internal energy of a gas increases when the gas is compressed]

air-cushioned vehicle :
a craft that rides on a cushion of air, is kept aloft by fans and driven forward by propellers; abbreviated ACV.

air embolism :
an obstruction (gas bubble, or other embolus) that has the potential to rupture a vessel or organ as a result of the increase in pressure when blood gases begin to expand or cease to circulate; a characteristic injury from breath holding during the ascent after a dive. Also called arterial gas embolism (AGE) or venous gas embolism (VGE).

air pressure :
the weight of air, calculated by the force exerted per unit area; measured at sea level the air pressure is 14.7 pounds per square inch (psi), decreasing with altitude and increasing with depth.

Aldis lamp :
a hand-held or portable signal lamp that's used to flash messages in Morse code; eponymously after the British inventor, A.C.W. Aldis.

alfa :
the phonetic representation of the letter 'A'; which is also represented by a maritime signal flag in the international code. When hoisted alone, the alfa burgee warns that there is a diver down (underwater), and other vessels should steer clear at slow speed; when accompanied by three numeral flags, this signal also includes the radius within which divers are working. [nb: "alfa" denotes the phonetic letter, "alpha" denotes the first in a series]

algorithm :
a set of rules for solving a problem in a finite number of steps; as the set of equations used in dive profiles and decompression tables to compute air supply, air mixture, underwater duration, and dive intervals.

Alluvium :
a deposit of sand, mud, and other sedimentary matter that's formed by the wash of flowing water, which has been deposited within recent times, especially in the valleys or outlets of large rivers.

alternate air source :
any device a diver can use in place of the primary regulator, in order to make an ascent while still breathing normally.

altitude diving :
underwater diving while at heights significantly above sea level, as when quarry or cave diving in uplands; the decompression stops used for dives at higher altitude are different from those used for the same dive profile at sea level.

aluminum :
a silver-white metallic element, lightweight and non-magnetic, ductile and malleable, and not readily corroded or tarnished, as used in alloys. [nb: one of the higher strength aluminum alloys is 5052, which has excellent forming characteristics and good corrosion resistance, including resistance to salt water; 6351-T6 is an aluminum alloy that's experienced air tank ruptures]

alveolus / alveoli :
the tiny bunched air sacs at the end of the bronchioles in the lungs where gas exchange occurs with the circulatory system.

ambient light :
the sunshine penetrating underwater, diminishing with depth and turbidity, that's used as illumination.

ambient pressure :
the surrounding pressure; being the effective pressure from the weight of the water and atmosphere around the diver at any particular depth. [nb: one atmosphere is approximately 14.7 pounds of pressure per square inch (psi)]

AMBU bag :
Artificial Manual Breathing Unit is the proprietary name for a manual resuscitator, a self-inflating bag, or a bag valve mask (BVM), which is a hand-held device used to provide positive pressure ventilation to persons who are not breathing or not breathing adequately; invented in 1953 by Holger Hesse and Henning Ruben for use by rescuers and medicos.

amidship / amidships :
in, at, or toward the middle part of a vessel or craft.

amphibian :
an airplane designed for taking-off from and landing on either land or water.

anadromous :
pertaining to fish that migrate from saltwater to spawn in freshwater; as distinguished from catadromous.

analog :
a mechanism that represents data by measurement to a continuous physical variable (eg: voltage, pressure, etc) and displayed on a readout by a pointer or hands on a dial.

anchor :
any heavy device or similar item that's dropped by a tethering chain or cable to the bottom of a body of water that's used for restraining the motion of a vessel or some other floating object; to be "at anchor" by holding fast or controlling motion.

anchorage :
a seaport or harbor with secure docking facilities for a ship.

anchor deck :
a small forecastle that houses the machinery for operating the anchors of a ship.

abbreviation for Association of Nitrox Divers International; also American Nitrox Divers Incorporated.

abbreviation for Adjusted No-Decompression Limit

anoxia :
the mental and physical disturbances that result from hypoxia, a lack of oxygen or suffocation.

Antarctic Circle :
a parallel of latitude that marks the farthest point (66.5°S) south of the equator where the sun appears above the horizon each day of the year.

anticoagulant :
an agent that inhibits coagulation, especially something that prevents blood from clotting or congealing; the use of such medications (including aspirin) is particularly dangerous to divers due to the barotrauma of air-filled body cavities.

abbreviation for Advanced Open Water, a scuba certification.

apparatus :
a combination of parts or mechanisms, instruments or machineries having a particular function; a complex device or group of devices that function together for a particular purpose.

aquaclude :
an earth layer that inhibits or precludes the passage of water, such as shale, or unfractured igneous and metamorphic rocks.

aqua-lung :
the name of the original open-circuit, self-contained, underwater breathing equipment, developed by Emile Gagnan and Jacques Y. Cousteau in 1942 during World War Two; consisting of a regulator and a high pressure air cylinder that supplied the required breathing gas at ambient pressure through a double-hosed demand valve. This system superseded the earlier attempts at constant-flow compressed-air breathing setups. [nb: "Aqualung" and "Aqua Lung" are registered trademarks of commercial products] [nb: the single-hosed scuba regulator was invented by Ted Eldred, an Australian, in 1953]

aquanaut :
a scuba diver who works for an extended period of time from and around a submerged dwelling.

aqueduct :
a conduit, canal, or artificial channel serving to conduct water from a distance.

aquifer :
a geological formation of permeable rock, gravel, or sand containing or conducting groundwater, especially one that supplies the fresh water for wells, springs, and the like.

Archimedes' principle :
a mechanistic theorem on relative displacement that states a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid, or a floating object displaces an amount of water that is equal in weight to the floating object; which is used by divers to calculate the buoyancy of an object.

Arctic Circle :
a parallel of latitude that marks the farthest point (66.5°N) north of the equator where the sun appears above the horizon each day of the year.

argon :
a colorless, odorless, chemically inactive, monatomic, gaseous element that makes up less than 1% of air; this inert element is often used as dry suit inflation in cold water due to its insulating properties.

arm :
an inlet or cove, as "an arm of the sea". Also, a curved piece on an anchor that terminates in a fluke.

artesian well :
a well in which water rises under pressure from a permeable stratum overlaid by impermeable rock.

arterial gas embolism :
a condition in which gas bubbles enter the arterial system and cause damage by blocking blood flow to vital organs, most commonly the brain, which most often occurs when air passes through the walls of capillaries and alveoli into the bloodstream; abbreviated AGE, and also called "air embolism".

articles of agreement :
a contract, between the captain of a ship and a crewmember, regarding stipulations of a voyage that's signed prior to and upon termination of a voyage; also called "shipping articles".

artificial respiration :
the stimulation of natural respiratory functions in a person whose breathing has failed by forcing air into and out of the lungs; to simulate, by various means, pulmonary ventilation.

artificial spit :
a commercial product that imitates the properties of a natural secretion; being small bottles of specially compounded liquid that's used by divers to keep the window of their masks defogged.

ascent bottle :
an extra or reserve gas cylinder that has been prepositioned to accommodate the mandatory in-water decompression stops on deep dives; also called stage bottle.

ascent / descent line :
an anchored line, suspended from a boat or buoy, that's used to control a diver's rate of ascent or descent, to provide orientation in strong currents and low light on deep dives, and to secure reserve gas cylinders for decompression stops; a type of safety line that's also called "drop line".

ascent rate :
the prescribed safe rate of ascent for off-gassing a diver is 30 feet per minute while rising to the surface.

asphyxiation :
the extreme condition (suffocation) caused by lack of oxygen and excess of carbon dioxide in the blood, produced by interference with respiration or insufficient oxygenated air; as derived from "stopping of the pulse". Also, to lose consciousness by impairing normal breathing; to cause to choke or smother, as by gas or other noxious agents.

astern :
situated behind something else, as being to the rear of a specified craft. Also, a backward direction.

abbreviation for American Society for Testing and Materials, being a standards organization that sets industrial measurements; for example, the ASTM 568A schedule identifies O-rings by a three digit suffix denoting their diameter and hardness.

abbreviation for Atmosphere Absolute, a measure of absolute atmospheric pressure.

athwart :
from side to side, across, crosswise; not aligned or adjacent.

abbreviation for a standard atmosphere; this established constant is approximately equal to the typical air pressure at earth mean sea level, and is defined as: 1 atm = 101325 Pa / 101.325 kPa, or 760 mm Hg, or 14.7 psi. [nb: a rule of thumb used by divers states that the pressure exerted by ten metres (33 feet, depending upon salinity) depth of water is approximately equal to one atmosphere]

atmosphere absolute :
the ambient pressure, including the barometric pressure of the air above the water; abbreviated ATA.

atmospheric pressure :
the normal amount of pressure exerted by the earth's atmosphere, being 14.7 pounds per square inch (called "one atmosphere") at sea level; also known as "barometric pressure". [nb: atmospheric pressure typically doubles at 33ft below sea level, and is halved at 18,000ft above sea level]

atoll :
a ring-shaped coral reef, or a string of closely spaced small coral islands, enclosing or nearly enclosing a shallow lagoon; previously called atollon.

At-Pak :
brand name of an early ScubaPro backpack-style buoyancy compensator that used lead shot for ballast, which was considered to be a more comfortable alternative to a lead weight belt; in an emergency, the shot could be unloaded by pulling a release pin.

abbreviation for the Australian Underwater Federation.

auxiliary bridge :
on large ships and ocean liners, a secondary room setup with duplicate controls that may be used as a substitute or reserve in case of need.

avast :
an imperative directive or command to stop or cease; perhaps derived from "hold fast".

avocational :
a certified volunteer who assists on a research or exploration project, such as marine archaeology or aquatic biology, as undertaken by students or professionals in other fields during their vacations so as to gain experience and advance knowledge.

Avogadro's law :
the principle that equal volumes of all gases at the same temperature and pressure contain the same number of molecules; thus the molar volume of all ideal gases at 0°C and a pressure of 1atm is 22.4 liters; named after Amadeo Avogadro. [nb: when the temperature of a gas is absolute zero, its volume is also zero]

Avogadro's number :
the constant (6.022 x 1023) representing the number of atoms in a gram atom, or the number of molecules in a gram molecule of a given substance; also called "Avogadro's constant".

abbreviation for Aquatic World Awareness Responsibility and Education, being a PADI nonprofit environmental foundation.

axial flow scrubber :
a type of treatment canister used in re-breathers where exhaust gas enters at one end and, after filtering, exits the other end.

A-yoke :
a tank valve that provides a high pressure seal between the tank valve and the regulator first stage, and works by compressing an O-ring between two metal seats; also known as a compressed O-ring valve, this yoke assembly holds the seal in place.

azimuth :
the horizontal deviation of a bearing (usually in "degrees") as measured from a standard reference (usually "magnetic north"); a compass heading or angle.

back-mount :
an equipment configuration wherein the air tanks are attached onto the divers back by a harness and backplate; as opposed to side-mount.

backplate :
a mounting plate, made of aluminum, steel, molded plastic, or ballistic nylon, through which the diving harness is threaded, and to which the air tanks and buoyancy compensator (BC) are mounted; the original design was by Greg Flannigan in 1979.

back roll entry :
see backward roll entry.

backup light :
an alternate or substitute source of illumination that's kept in reserve for an emergency, being a redundancy precaution.

backwash :
water thrown backward by the motion of oars, propellers, paddle wheels, or any other means of propulsion. Also, to clean something out, such as a clogged filter, by reversing the flow of fluid passing through it. Also, a condition, or the effects of a condition, usually undesirable, that continues long after the event which caused it; aftermath, consequence, result, upshot.

backward roll entry :
a self-protective water entry method in which the fully equipped seated diver rolls off the side or stern of the boat, allowing the back-mounted air tanks to strike the surface first, while the diver's body is in a tuck, face mask held in place, and then continues the roll underwater into a prone swimming position; any extra gear or bottles ride in the diver's protected "breadbasket" for a safe and secure entry; also called "back roll entry" or "flip-flop entry".

backwater :
water held or forced back, as by a dam, flood, or tide. Also, to halt or reverse the forward movement of a vessel by applying opposite propulsion; backwash. Also, to literally back up, as to retreat, or to figuratively back down, as to back-pedal. Also, an isolated or stagnant place that has been literally or figuratively bypassed; undeveloped, regressive, or backward.

bail-out bottle / bailout bottle :
an air cylinder containing an emergency supply of breathing gas that's used to escape from trouble with the primary air supply.

ballast :
a heavy material (including sea water) carried on a vessel to control draft and stability. Also, a heavy material (eg: lead weights) carried by an underwater swimmer to control depth and trim.

ballistic nylon :
a high-performance synthetic thermoplastic material that's characterized by strength and elasticity, resistance to abrasion and chemicals, low moisture absorbency and a capacity to be permanently set by heat; this tough polyamide fabric is tear resistant and was introduced during WWII as protection against flying debris.

bank :
a broad seafloor elevation (eg: sandbank) around which the water is relatively shallow, but not a hazard to surface navigation.

bar :
a centimeter-gram-second unit of pressure (term derives from "weight") that's equal to one million dynes per square centimeter (15 psi, 101 kPa); used by divers to represent the force exerted upon a given area, and equivalent to the force of one atmosphere (1 ATA = 1.0132 bar). Also, a long ridge of sand (ie: sand bar), gravel, or other material near or slightly above the surface of a body of water, often an obstruction to navigation.

Barisal guns :
the name given to mysterious booming sounds that seemingly come from nearby occurrences at sea, being situated offshore from Barisal (Eastern Bengal), Bangladesh.

barometric pressure :
atmospheric pressure affected by weather, as measured by an aneroid barometer, wherein standard atmospheric pressure has a value that's equivalent to the pressure exerted by a column of mercury 29.92 inches (760 mm) high, or 1013 millibars (101.3 kilopascals).

barotrauma :
injury, generally to the middle ear or paranasal sinuses, resulting from imbalance between ambient pressure and that within the affected cavity.

barrier island :
a broadened barrier beach, which may be habitable in places, that provides a measure of protection for the mainland, as during hurricanes and tidal waves.

basin :
a partially enclosed, sheltered area along a shore where boats may be moored. Also, a natural or artificial hollow place containing water.

bathing suit :
a garment worn for swimming or for recreational activities in and around water; also called swimsuit or swimming suit.

bathyal :
pertaining to the biogeographic region of the ocean bottom between the sublittoral and abyssal zones; from depths of approximately 660 to 13,000 feet.

bathyscaphe :
a navigable submersible vessel, with an observation chamber in its hull, that's used for exploring the ocean's depths; coined by Auguste Piccard.

batten :
a thin or narrow strip of lumber attached to sailcloth to keep it flat or taut. Also, to cover a hatch or other opening so as to make it watertight.

bay :
a body of water that forms an indentation in the shoreline, which is larger than a cove but smaller than a gulf. Also, in the south Atlantic statesregion, an arm of a swamp.

BC :
abbreviation for Buoyancy Compensator.

abbreviation for Buoyancy Control Device; enables the diver to regulate buoyancy to control depth, and acts as a flotation device on the surface.

beach :
an expanse of sand or pebbles along a shore, often washed by the tide or waves. Also, to haul something or run a boat onto the shore. Also, to cause to be unemployed or idle; as "on the beach".

beachmaster / beach master :
the person responsible for the accountability of persons and equipment on shore, and in charge of the on shore work party; more commonly called a 'dive marshal'.

belay :
to fasten by connection or attachment so as to make secure, especially a rope or line used by someone for descent or ascent. Also, an imperative directive to stop or cease, desist or quit. Also, a secure object or other safe projection that's sturdy enough to anchor a rope or line under a full load.

beam :
the maximum width (breadth) of a ship at its widest part.

Beaufort scale :
a scale indicating the speed or force of wind, enumerated 0-12 or 0-17, commonly expressed as "Force #"; devised by British Admiral Francis Beaufort around 1855.

beaver :
a piece of neoprene fabric that hangs down in the back on a wet suit jacket and is drawn forward between the legs to attach to the front, covering the diver's crotch; also called "beaver tail" and "butt flap".

beach drift :
the drifting of marine sediments in patterns parallel to the contours of a beach, due to the action of waves and currents; also called "littoral drift" or "longshore drift".

bearing :
a horizontal direction, expressed in degrees, east or west of the true or magnetic north (or south) direction. Also, one's relative position or direction, often expressed as "bearings".

bends :
common term for decompression sickness (DCS) or aeroembolism. Also, the wales of a vessel; thick planking immediately below the waterways of a wooden vessel.

benthos :
the biogeographic region that includes the bottom of a lake, sea, or ocean, and the littoral and supralittoral zones of the shore; also known as benthic division or benthonic zone.

bergy bit :
a small iceberg, somewhat larger than a growler.

berth :
a shelflike sleeping space aboard ship. Also, the space, at a safe distance from shore, that's been allotted for a vessel to dock or lie at anchor; a water surface mooring area that's delineated by either floating or fixed dock structures, for the purposes of embarking, disembarking, and the wet storage of a recreational boat. Also, a job or position; a place or situation of employment.

bezel :
the angled rim surrounding the face of a watch or compass, especially a rotating ring that can serve to mark time or indicate position; as derived from 'bevel' or 'chamfer'.

bight :
a looped or slack part of a rope. Also, a bend or curve in the shoreline of a sea or river. Also, a body of water bounded by such a bend, as a bay or gulf.

bilge :
either of the rounded areas that form the transition between the bottom and the sides on the exterior of a hull; derived by alteration of "bulge". Also, an enclosed area at the bottom of a vessel where seepage collects; usually called "bilges". Also, the seepage collected in this space; also called "bilge water". Also, slang for foolish talk or worthless ideas; nonsense, claptrap, malarkey, confetti, snow, blow smoke.

bilge keel :
a keellike projection along a ship's bilge to retard rolling; also called "baby keel".

billethead :
a carved ornamental scroll or volute, terminating a stem or cutwater at its upper end, in place of a figurehead; also called scrollhead.

billow :
a great wave or surge of the sea; as derived from 'bulge'. Also, to swell or rise, wax or expand, heave or undulate, as when blown by the wind.

bimini / bimini top :
a protective canopy without side panels or drapes that's supported by scantling over the cockpit of a boat.

black water :
the dark depths of sea water that's below the level of penetration of sunlight; being at or below a depth of 90ft or two atmospheres of pressure. Also, clear or frothy water running underground in a stream where navigation thereupon cannot be aided by natural illumination.

black-water rafting / blackwater rafting :
quickly moving over or through frothy rapids along an underground passage where natural illumination cannot aid in navigation; also called "cave tubing", the participants are usually outfitted in wet suits and life jackets while riding in an inflated dinghy.

bladder / air bladder :
the inner air cell of a buoyancy compensator (BC), which holds the necessary amount of air used to provide proper neutral buoyancy at depth.

blind roller :
a long oceanic swell that almost rises to breaking as it passes over shoals.

blink :
a brightening of the base of a cloud layer caused by the reflection of light by snow or ice, as derived from gleam, twinkle, glitter, or shine.

block :
a housing or part enclosing one or more freely rotating, grooved pulleys, about which ropes or chains pass to form a hoisting or hauling tackle; also known as "tackle block" or "block 'n' tackle". Also, an obstruction, obstacle, hindrance, or stoppage.

blue hole :
a sinkhole in a lake or the sea which is subject to tides, causing its flow to reverse; such sinkholes are often the entrance to a cave.

blue jacket :
informal designation for a seaman or sailor, by reference to his blue duffel or pea jacket.

blue nose :
a ship that has crossed the Arctic Circle (between the North Frigid Zone and the North Temperate Zone) or Antarctic Circle (between the South Frigid Zone and the South Temperate Zone), so called from painting the hawsepipes blue, as being representative of the cold; the ship's company of such a voyage may be called "blue noses". [nb: alternatively, the "Order of the Blue Nose" is reserved exclusively for the Arctic Circle, and the "Order of the Red Nose" exists as an exclusive distinction for the Antarctic Circle]

blue water :
nautical reference to the open sea, or oceangoing; also represented as "deep water", and sometimes spelled "blue-water".

bluff :
a bold coastline or precipitous headland. Also, a full blunt bow on a vessel. Also, a cliff or headland with a broad steep face.

board :
the side of a ship; or the windward tack of a ship's course.

boarding float :
a platform-type structure, either floating or fixed, stationary or adjustable that's designed for short-term moorage of boats, and to facilitate pedestrian access to and from boats in the water; it's located on, along side of, or near a boat launch ramp; also known as a boarding pier (qv).

boarding ladder :
any stairway, ladder, net, or similar construction used to accommodate the ingress or egress of people over the side of a ship.

boarding party :
a group of persons who board a vessel, especially to attack, seize, or search it.

boarding pier :
the portion of a pier where a boat is temporarily secured for the purpose of embarkation or disembarkation.

boat deck :
a superstructure deck on which most of the lifeboats of a ship are stowed.

boat dock :
a boat slip or berth (qv).

boating party :
a group of persons who board a vessel for transport or recreation, especially when paying for the privilege.

boat launch ramp :
a sloped surface at the edge of a body of water that's designed and constructed (usually paved) for the launching and retrieval of trailered boats and other watercraft.

boat ramp :
a boat launch ramp (qv).

boat slip :
a boat dock or berth (qv).

boatswain's chair :
a wooden plank or canvas seat that's hung by ropes over the side of a ship's rail, deck, bridge, and the like for stable access while performing construction, maintenance, or rescue work.

boatswain's locker :
a storage compartment, usually located forward, where tools, line, and other small equipment for working on deck is stowed.

boatswain's pipe / boatswain's whistle :
a simple musical device used by the boatswain to make shipboard announcements over the public address (PA) or loudspeaker system.

bollard :
a substantial post on a wharf or deck ("bitt") made of wood, metal, or concrete that's used for mooring vessels.

a mnemonic acronym for the in water check performed prior to diving: Bubbles (manifold and valve check), Out of air (S-drill), Lights, Turn Time (Thirds).

bolt snap :
a hardware device, made of brass or stainless steel, that has a spring-loaded thumb-gate, can be double ended or have a swivel on one end, that's used to clip items to the diver's harness; also known as a piston bolt.

bombiti / baturlio marina :
the name given to mysterious booming sounds that seemingly come from nearby occurrences at sea, being situated off certain coastal sites in Italy.

boom :
any of various spars, beams, or poles projecting from a mast, as used to extend a ship's sails, to handle cargo, to guide objects, or to hold devices; also called a derrick or crane, an arm or stick. Also, a chain, cable, or the like serving to obstruct navigation.

boot :
a plastic footing that fits on the rounded bottom of a scuba tank that allows it to be stood upright without support; not used in cave diving due to being an entanglement hazard.

bootie / bootee :
a waterproof (neoprene) sock-like foot covering, serving to insulate and protect the diver's foot and ankle, that's worn inside open-heeled flippers or fins; also called "footie".

boottop / boottopping :
a distinctive band of paint covering the area between the water lines of a ship when fully loaded and when unloaded; also called load-line mark or plimsoll mark.

booty :
slang for an unexplored ("virgin") cave.

bottle :
slang for the cylinder, usually steel or aluminum, of pressurized breathing gas that's used in scuba diving; a portable tank containing compressed air for breathing underwater.

bottom mix :
the breathing gas specified for the deepest depth of a dive, such as air, nitrox, or helium, usually when other decompression gases are present.

bottom time :
the elapsed time between a diver descending below the surface to the beginning of the return ascent; also called actual bottom time (ABT).

bottom timer :
a pressure activated timing device, mechanical or electronic, that automatically starts measuring bottom time when a diver descends underwater.

bounce dive :
in recreational diving, a descent to a specific depth, often the seafloor maximum, that's immediately followed by a return ascent back to the surface with the least delay, which is represented in a dive profile resembling a spike; also called a "yo-yo dive". In commercial diving, the alternative to saturation diving.

bourdon tube :
a spiral or c-shaped tube that changes its shape when pressure increases at depth; used in depth gauges to alter the position of the denotative indicator as the tube changes shape; derived from the drone or low-pitched tone emitted by musical instruments.

bow :
the front of a craft or vessel; designated by the color white; also called prow or stem. Also, the abbreviation for Basic Open Water, a scuba certification. Also, the foremost oar, situated at the forward end, when rowing a boat.

bower :
an anchor carried at the bow of a vessel.

bowsprit :
a spar projecting from the upper end of the bow of a sailing vessel, for holding the tacks of various jibs or stays, and often supporting a jib boom; as derived from bow pole.

boy :
an apprentice seaman or fisherman, especially one who has not before gone to sea (eg: cabin boy).

Boyle's law :
the principle that, for relatively low pressures, the pressure of an ideal gas kept at constant temperature varies inversely with the volume of the gas; named after Robert Boyle, it's also called Mariotte's law; also expressed as PV=k (Pressure)(Volume) = (constant of proportionality), or PV=nRT.

braided line :
woven nylon line that has better abrasion resistance than twisted line.

brash ice :
small, brittle fragments of suspended sea ice or floating river ice; also called brash.

breaker :
a wave that breaks into foam, either at an offshore surfline or upon shoals or the shore.

breaking strength :
the load that will cause a line or rope to fail.

breakthrough :
indicates the entry of carbon dioxide into the inhalation side of the breathing loop from the absorbent canister on a re-breather.

breakwater :
a barrier that breaks the force of incoming waves, as before a harbor or bay. [nb: this term has been mistakenly used to mean "where waves break" before a shore or upon shoals; which is properly known as 'surf' or 'surfline']

breath-hold diving :
underwater diving without supplemental air or breathing equipment; also called free diving or skin diving.

breathing loop :
the part of a re-breather system that includes the mouthpiece, hoses, inhalation bag, exhalation bag, and absorbent canister.

breech :
the end of a block or pulley farthest from the supporting hook or eye.

breeches buoy :
a life preserver with a pants-like canvas seat for hauling a shipwrecked or disabled person on or off a vessel; also called "britches buoy".

bridge :
a structure spanning and providing passage over an opening or past an obstacle. Also, the platform from which a vessel is controlled and navigated.

bridge deck :
a deck on top of a bridge house; also called a flying bridge. Also, the deck from which a vessel is usually operated; the location of the pilothouse. Also, the first deck in a bridge house.

brightwork :
the polished metal parts on a ship. Also, all plain or varnished woodwork that is kept scoured on a vessel.

brine :
the sea or ocean; the water of the sea. Also, water saturated or strongly impregnated with salt; any saline solution. [v: brackish]

broach :
to veer to windward. Also, to break the surface of water from below, such that the rudder cannot be used to steer.

brow :
a gangplank, gangway, or passageway. Also, the edge of a steep place or drop-off, as a brink or brim, by analogy with the brow of the head.

brown water :
nautical reference to shallows, shoals, littoral or estuarial waters.

abbreviation for British Sub-Aqua Club, a club-based organization that has served, since 1953, as the governing body for the instruction and practice of recreational scuba diving in the United Kingdom.

bubblehead :
slang for a submariner; also known as a dipper, boomer, or dolphin.

buddy :
a diving partner, or the member of a team or group who's designated to be a safety companion.

buddy bottle :
an independent stage bottle that's carried for emergency breathing gas on solo dives instead of a dive partner.

buddy breathing :
the sharing of the same demand valve by two or more divers, generally after an out-of-gas emergency.

buddy check :
the inspection by one diver of another's diving equipment to ensure that it's properly configured and functioning correctly; this procedure is conducted before the start of the dive.

buddy diving :
underwater diving with a designated partner (not just swimming in a group) so as to improve each diver's chance of surviving an accident by the shared observance of proper procedures and safety precautions; also called "backup" or buddy system.

bugeye :
a ketch-rigged (ie: two masted with the larger mainmast forward) sailing vessel; so called after the former practice of painting a large eye on each side of the ship's bow.

bulkhead :
a reinforced wall-like vertical partition inside ships and aircraft that separates compartments, often air- or water-tight.

bull rail :
a low continuous safety rail, slightly raised and blocked, running along the edge of a boat deck, berth, dock or pier; as used for tying on mooring lines to prevent drifting, or for bracing carts and carriers, objects or people to prevent them from falling overboard; sometimes called a "curb" or "curbing".

bull's-eye :
a small circular opening or window set into a roof, ship's deck or overhead, to admit light; sometimes called "deadlight".

bull's-eye squall :
a squall forming in fair weather that's characterized by the peculiar appearance of the small isolated cloud marking the top of the invisible vortex of the storm.

bulwarks :
a protective wall enclosing the perimeter of a deck, especially the main or weather deck.

bum boat / bumboat :
an unofficial supply boat, such as a commercial one hired locally for deliveries, but often one that purveys curios and souvenirs to visiting ships.

buntline :
one of the ropes attached to the foot of a square sail for hauling it up to the yard so it can be furled.

buoy :
an anchored float used as a marker or as a mooring, as derived from "boye a float", beacon [v: cresset]. Also, any of various buoyant devices for supporting a person in the water, as a "life buoy" or "life preserver".

buoyancy :
upward pressure exerted by the fluid in which a body is immersed, or the amount of lift acting on a submerged object, being that force equal to the weight of the water displaced by the object; submerged objects that float are positively buoyant, those that sink are negatively buoyant, and those that remain at a level are neutrally buoyant.

buoyancy compensator :
a vest, jacket, or backpack containing a distensible air bladder that can be inflated and deflated to regulate a diver's buoyancy underwater; also called buoyancy control device (BCD).

buoyancy control :
the ability to maintain neutral buoyancy while swimming at any of various depths determined by the diver; problems include: fluctuating currents, changing temperature, altered weight or load, defective BCD bladder or valve, mis- or maladjusted BCD, inexperience. An essential skill of practical diving technique.

burgee :
a small nautical flag or pennant that's used for identification or as a signal; derived from a mark of the owner.

burst disk :
a safety release fixture located on the valve of a scuba tank that prevents over-pressurization of the tank, and provides visual confirmation of the breach by its deformation; a thin copper disk that's held in place by a venting plug, which is designed to rupture if the tank's pressure is greatly exceeded. [nb: according to the first law of thermodynamics, the internal energy of a gas increases when the gas is compressed]

burton :
any of various small tackles rove in a particular way for use on shipboard; a metathetic variant of breton or briton (tackle).

butt-mount :
secure placement of the canister battery pack for the large primary dive light onto the bottom of a back-mount or side-mount air cylinder, instead of attaching it to the equipment belt or harness.

Bag Valve Mask; see AMBU bag.

a mnemonic for "Begin With Review And Friend" that's used in PADI training.

bypass valve :
a manual inlet control mechanism that permits the diver to add gas into the breathing loop on a re-breather.

cable :
any strong heavy rope or cord made of twisted strands, especially one made with metallic wire. Also, a thick hawser made of rope, wire, or chain. Also, a strong heavy rope or cord that operates a mechanism. Also, a unit of length equal to 720 feet on land, or 606 feet at sea. [nb: 12 inches = 1 foot, 3 feet = 1 yard, 6 feet / 2 yards = 1 fathom, 16.5 feet = 1 rod (aka: pole or perch), 66 feet / 4 rods = 1 chain (90 feet / 15 fathoms = 1 anchor chain), 10 chains / 660 feet (1/8 statute mile) = 1 furlong, 120 fathoms / 720 feet = 1 land cable, 101 fathoms / 606 feet (1/10 nautical mile) = 1 cable, 3 statute miles = 1 land league, 3 nautical miles = 1 sea league / shot]

abbreviation for Cerebral Arterial Gas Embolism.

caisson :
a protective environment for working underwater, consisting of a pressurized watertight chamber. Also, a watertight structure built against a damaged hull to render it watertight; also known as cofferdam. Also, a float for raising a sunken vessel; also known as a camel or pontoon. Also, a boatlike structure used as a gate for a dock or the like.

calf :
a mass of ice detached from a glacier, iceberg, or floe.

cam band :
a webbing strap with a cam-action tensioning buckle that's generally used to secure a diving cylnder to a backplate, a BC vest or BCD jacket, or some other diving harness.

camel :
a float for lifting a deeply laden vessel sufficiently to allow it to cross an area of shallow water; such a buoyancy float is also called a pontoon. Also, a float serving as a fender, as between a vessel and a pier.

canal :
an artificial waterway used for navigation, irrigation, or other application. Also, a channel or other watercourse, such as a long narrow arm of the sea that penetrates far inland.

canister :
a small, special purpose container, such as the absorbent canister of neutralizing substances for filtration in a re-breather system, or the housing for the battery pack of a large and powerful dive light.

canister light :
a large and powerful dive light with a battery pack contained in a canister, which typically has a longer and brighter period of illumination than the smaller flashlight-style lights. A type of dive light wherein the battery pack is strapped to the diver's belt or harness while this primary light is hand held; the battery pack for such a large light may also be attached to the bottom of a back-mount or side-mount air cylinder.

canoe :
any of various small, slender, open boats, tapering to a point at both ends, propelled by paddles or sometimes sails, and traditionally formed of a light framework that's covered with bark, skins, or canvas, or formed from a dug-out or burned-out log, with or without outriggers, or now made of aluminum, fiberglass, and the like, as used for transport, touring, or recreation.

canoe diving / kayak diving :
use of a small lightweight vessel for access to remote or obscure dive sites, especially rivers, as when drift diving; an alternative to boat or shoreline access.

cape :
a piece of land jutting into some large body of water, as a point or headland, promontory or spit. Also, a ship that has good steering qualities.

Cape Horn fever :
an illness feigned by malingerers.

capillary :
one of the minute blood vessels between the terminations of the arteries and the beginnings of the veins where the gas exchange takes place between the bloodstream and the tissues or the air in the lungs.

capsize :
to turn bottom up, to keel over or overturn.

capstan :
any of various windlasses, rotated in a horizontal plane by hand or machinery, used for winding in ropes, cables, and the like.

carbon dioxide :
a colorless, odorless, incombustible gas that's present in the atmosphere and formed during respiration; it's a metabolic byproduct of oxygenation that can stimulate respiration or depress the central nervous system.

carbon monoxide :
a colorless, odorless, poisonous gas that's produced when carbon burns with insufficient air; its toxicity derives from its affinity for hemoglobin, which competitive bond denies oxygen availability to tissues during inhalation.

careen :
to cause a vessel to tip, lean, list, sway, or heel over to the side. Also, to clean or repair the hull of a vessel by laying onto its side. Also, a headlong rush, as rash, impetuous, or uncontrolled action.

cargo bay :
the large central area of a transport vehicle, vessel, or craft in which payloads and support equipment are carried; also known as "cargo area", "payload bay", or bay.

cargo net :
a flexible open-weave mesh, fabricated of fiber or wire, that is used to conveniently secure, sling-load, or otherwise handle loose objects that are transported to or from a cargo bay, hold, or other receptacle. Also, such a mesh used when scaling, as during insertion or extraction, ingress or egress, but especially during debarkation from or embarkation of a transport ship.

castoff / cast-off :
to let a ship go, to loose a vessel from its mooring, or to launch a boat; also known as shove-off or simply cast, as derived from 'throw'. Also, to turn the head of a sailing ship away from the wind, especially when getting underway or during departure. Also, to discard, reject, or abandon people or things, as a castaway.

catadromous :
pertaining to fish that migrate from freshwater to spawn in the saltwater sea; as distinguished from anadromous.

cathead :
a projecting timber or metal beam to which an anchor is hoisted and secured.

cat's-paw :
a light breeze that ruffles the surface of the water over a small area. Also, a hitch made in the bight of a rope to hold the hook of a tackle.

catwalk :
a narrow walkway, especially one positioned high above the surrounding area, used to provide access or allow movement.

caustic cocktail :
a dangerous side-effect from water flooding the scrubber cylinder of a re-breather, combining with the hydroxide chemical (or other carbon dioxide absorbent) to form a poisonous alkaline gas that can burn the mouth or trachea if inhaled.

cave :
a hollow in the earth that opens more or less horizontally, and is large enough to admit the passage of a person. Also, to cause supporting material to collapse or overlying material to fall (cave-in).

cave arrow :
designation for line markers that have been emplaced as a safety precaution to guide swimmers toward the exit; directional line markers that point the way to an exit.

cave diving :
swimming underwater into an overhead environment (including caverns and grottoes, natural springs and sinkholes, mines and aqueducts), where the exit is not always visible; an underground excursion that requires specialized training and equipment.

cave fill :
the practice of overfilling a scuba cylinder to a pressure significantly above the rated safe working pressure (charging pressure) so as to extend bottom time (ABT) where an excess of equipment is not possible, which filling practice is illegal in some jurisdictions, and significantly increases the risk of catastrophic failure of the air tank.

cave line :
any braided synthetic cord of small diameter that's used by scuba divers as a means of returning to a safe starting point in underwater conditions of low visibility, or where navigation is difficult (due to water currents or route circuity); also called guideline, safety line, distance line, or penetration line.

cave reel :
a spool containing braided synthetic cord that's used to lay and recover long lengths of cave line as a safety line or guideline marking the route and exit for a cave or cavern, wreck or other entanglement.

cavern :
a large cave that's mostly or entirely underground, containing two or more rooms that're interconnected; a large cavity or passage, naturally occurring with interconnected rooms, the outermost being illuminated by daylight.

cavern diving :
swimming underwater into a large overhead environment where the outermost chamber is illuminated by daylight, such that the exit remains directly or indirectly visible; an underground excursion that requires specialized training and equipment.

cavitation :
the rapid formation and collapse of pockets of vapor in a flowing liquid of very low pressure, often causing structural damage to propellers, pumps, and related mechanisms. Also, the formation of cavities, especially in some part of the human body; as derived from cavity.

cay :
a small low island; often called 'key'.

C-card :
contraction of Certification card, which is a summary representation by an authorized agency as evidence that the bearer has completed a certain level of diver training.

abbreviation for Closed-Circuit Re-breather.

abbreviation for the Cave Diving Association of Australia.

celsius :
a temperature scale in which 0 represents the freeze point and 100 the boiling point; also called centigrade. [nb: the degree intervals of the kelvin scale are the same as celsius, as the rankine are the same as fahrenheit]

CE mark :
European manufacturing certificate of approval, as used in product sales.

cenote :
the Spanish term (meaning "deep thing") for a limestone sinkhole [Maya: dzonot], a type of submarine cavern that's afresh water aquifer; cenotes may be located entirely underground, partly submerged, at ground level, or as open wells, and are often connected to other bodies of water.

certificate of admeasurement :
a government document showing the registered tonnages of a commercial vessel.

abbreviation for Controlled Emergency Swimming Ascent, which involves exhaling while swimming toward the surface, when no other air is available, so as to prevent lung expansion injury from breath holding when a diver is out of air.

chain :
a sequence of metallic rings that pass through one another and are linked together for use in securing, supporting, or hauling. Also, a surveyor's measure for establishing distance by a 100 foot (30m) or 66 foot (20m) length, wherein each link is exactly the same as every other, for ready and consistent computation. [nb: 12 inches = 1 foot, 3 feet = 1 yard, 6 feet / 2 yards = 1 fathom, 16.5 feet = 1 rod (aka: pole or perch), 66 feet / 4 rods = 1 chain (90 feet / 15 fathoms = 1 anchor chain), 10 chains / 660 feet (1/8 statute mile) = 1 furlong, 120 fathoms / 720 feet = 1 land cable, 101 fathoms / 606 feet (1/10 nautical mile) = 1 cable, 3 statute miles = 1 land league, 3 nautical miles = 1 sea league / shot]

chain locker :
a storage compartment for the proper stowage of cable and hawser aboard a vessel.

chandler :
a trader in specialized supplies (eg: ship chandler). Also, a maker or seller of candles (wax) or soap (tallow); as derived from 'chandelier'.

channel :
the bed of a stream, river, or other watercourse or waterway. Also, the deeper part of a waterway, especially the navigable route between two bodies of water. Also, an artificial waterway constructed and maintained for the safe passage of navigable vessels. Also, a wide strait, as between a continent and an island. Also, a horizontal timber or ledge built outboard from the side of a sailing vessel that's used to spread shrouds and backstays outward; by alteration of "chain wale" (chain-wale).

channeling :
the settling of the absorbent chemical in an improperly packed scrubber canister of a re-breather; as the absorbent material settles, a passageway for the exhaled CO2-rich gas passes through the scrubber without being filtered ... this is not a significant problem in cartridge-style scrubbers.

channel marker :
a colored or numbered buoy, or other aid to navigation, that's located alongside a navigable waterway to ensure safe passage; also called daymark (green or red), can buoy (numbered odd, colored green), or nun buoy (numbered even, colored red). [nb: pass along marked channels by staying left of the red signals and right of the green signals, or by keeping the red signals on the red side of the boat and green signals on the green side of the boat]

chantey / chanty :
a rhythmic work song, especially used by sailors.

charging pressure :
a rating, permanently marked on the container, indicating the maximum allowable gauge pressure that may be applied at the time of filling with breathing gas; the maximum safe working pressure for a scuba cylinder.

Charles' law :
the principle that the volume of an enclosed gas is directly proportional to its absolute temperature, or V=kT (Volume) = (constant of proportionality)(Temperature); also known as Gay-Lussac's law. Also, if pressure is constant, the volume of a gas expands by a constant fraction as temperature increases.

chart :
a hydrographic or marine map.

chart datum :
the level of the lowest tide at a particular place, recorded with heighths and depths of tides; abbreviated CD.

charter :
an arrangement by which all or part of a ship, or other conveyance, is leased for a particular group, journey, or activity. Also, the trip, journey, tour, or expedition made using such an arrangement.

chart table :
the desktop surface, typically horizontal, used for displaying a marine or hydrographic map, a nautical chart, which is consulted for known hazards, and upon which an intended course is planned or the actual course is plotted; the modern electronic version is known as the "central navigation console".

check valve :
a valve that only allows fluids or gases to flow in one direction, such as the mushroom valve in a second stage regulator, and in the hose assembly of a re-breather, on both the inhalation and exhalation sides of the loop to keep the gas flowing in the proper direction.

chicken ladder :
slang for an inclined plank with transverse traction cleats that's used as a temporary bridge onto a vessel; a brow or gangplank, walkway or passageway.

chine :
an angular intersection of the sides and bottom of a vessel; or a longitudinal member running behind this intersection.

chock :
a wedge to fill-in a gap or a device to brace an object, any support or reinforcement; also called "chock block", and derived from "choke", as close or tight.

chockablock :
having the blocks drawn close together, as when the tackle is hauled to the utmost; crowded together, close or tight.

chop :
the short irregular motion of a turbulent wave. Also, the rough water of a turbulent lake or sea.

Christmas tree ladder :
slang for a boarding ladder formed of a single central rail with rigidly cantilevered rungs extending outward to the sides, which permits use while wearing swimfins.

chum :
an inexperienced or novice sailor, especially someone on his first float or cruise; also called pollywog, nugget, or fresh catch.

chumming :
slang for vomiting overboard when seasick, after the fishing practice of dumping bait in the water to attract fish.

clear the decks :
the removal of everything not required so as to have ready access during seaborne operations.

cleat :
a strong device, usually metal with one or more projections, that's used to secure tie-downs, as on a deck or pier [dock cleat] for mooring. Also, a wedge-shaped block or strip of resistant material fastened to a surface to serve as a check (belay) or support; also called a chock. Also, a resistant strip fastened across a surface, as on a ramp [gangway cleat], to provide sure footing.

clew :
either lower corner of a square sail, or the lower after corner of a fore-and-aft sail. To "spread a large clew" is to carry a large amount of sail, which will present an impressive appearance.

clew down :
to secure a sail in an unfurled position.

clew up :
to haul the lower corner(s) of a sail up to the yard by means of (clew) lines.

closed-circuit / closed-circuit system :
an underwater breathing system which does not release exhaled gasses as exhaust, but filters and recycles the discharge back into the gas supply; also called "closed-circuit re-breather". Closed-circuit re-breathers generally supply two breathing gases to the loop: one is pure oxygen and the other is a diluting gas (diluent), such as air, nitrox, or trimix. The major task of the closed-circuit re-breather is to control the oxygen concentration, known as the oxygen partial pressure, in the breathing loop and to warn the diver if it is becoming dangerously low or high as depth changes.

closed-circuit re-breather :
an intact cycle of breathing gases that produces no discharge of bubbles and enables long duration dives, as used by many military and some recreational divers, especially photographers. Re-breathers using a fully closed-circuit generally supply two breathing gases to the breathing loop: pure oxygen and a diluent (eg: air, nitrox, or trimix), and control the oxygen partial pressure concentrated at any underwater depth. In fully automatic closed-circuit systems, a metering mechanism injects oxygen into the breathing loop when it detects that the oxygen concentration has fallen below the required level. Alternatively, the diver may be able to manually control the mixture by adding diluent gas or oxygen, but this is a risky adjustment that can produce dangerous results with only small volumes added.

closed-circuit SCUBA :
a self-contained scuba system that allows divers to re-breathe exhaled air after the removal of CO2 and the addition of supplemental O2; in contrast with an 'open-circuit' system, closed-circuit scuba is noiseless and produces no exhaust bubbles.

close-hauled :
to sail a vessel as close to the wind as possible, with sails as flat as possible.

abbreviation for Confederation Mondiale des Activitias Subaquatiques; the World Federation of Underwater Activities, established in 1959.

coaming :
the protective rim or raised bulwark surrounding an opening in a bulkhead or deck that's designed to exclude water; also called a "knee-knocker" or "shin-scraper".

coast :
the land beside the sea, as a shore, often serving as a border; also known as "coastline", and derived from "side wall". Also, to be sustained or to continue on acquired momentum.

cockpit :
a sunken, open space, generally in the after part of a small boat, that provides access to the controls and instruments needed by the crew when operating a vessel at sea.

cold harbor :
a place of refuge or retreat, typically primitive, that lacks the usual amenities, especially fresh water and other creature comforts; such a haven is also called a cold camp or fly camp.

collapse depth :
the design depth beyond which the hull structure of a submersible is presumed to suffer catastrophic failure to the point of total collapse; such "crush depth" is referenced to the axis of the pressure hull, and is affected by material defect or decline, by hull penetrations, or by other relevant factors.

comber :
a long curling wave.

command signal :
a signal from one diver that requires a response from another diver; including: OK, Hold, and Surface. The OK hand signal is formed by connecting the thumb and forefinger in a circle with the other three fingers extended, or by making a circular motion with the dive light. The Hold hand signal is a closed fist. The Surface (turn the dive and exit) hand signal is an upward pointing thumb with the other fingers in a fist; such termination is also called "thumbing the dive".

companion / companionway :
a stair or ladder within the hull of a vessel; a raised and hooded hatchway transitioning from the deck to the cabin(s) of a ship.

compartment :
a partitioned area or space, as a cabin or hold on a vessel.

computer :
see dive computer.

confluence :
a flowing together of two or more streams, rivers, or the like into a singular course or unified movement. Also, their place of [con]junction into a body of water formed by such confluence.

conning tower :
the housing over the main entrance to the interior of a submarine, accommodating its periscope and antennas, and used as an observation platform; also called the "sail" or fairwater.

constriction :
a narrow passage or small opening that's not large enough for two divers to swim through together (ie: minor constriction); or that requires gear removal to negotiate (ie: major constriction); also known as a squeeze, restriction, tight, sidemount passage, no mount.

continental margin :
the offshore zone that separates the dry-land portion of a continent from the deep ocean floor, consisting of the continental shelf, slope, and rise (qqv).

continental rise :
the gently sloping transition between the continental slope and the deep ocean floor, usually characterized by the coalescence of submarine alluvial fans.

continental shelf :
the part of a continent that's submerged in relatively shallow sea; contiguous land that's underwater.

continental slope :
a steep slope separating a shallow continental shelf and a deep ocean basin.

controlled buoyant lift :
an underwater rescue technique that's used for safely raising an incapacitated diver to the surface.

convection :
the vertical flow of air, water, or the like, which often entails a change of temperature or humidity; as distinct from advection.

cordelle :
a heavy rope formerly used for towing boats on rivers; derived as a diminutive of 'cord', cordelling is one of the methods of hauling a watercraft upstream.

counter lung :
the breathing bag portion of a re-breather system, which is so-called because it operates counter to or opposite of the diver's lungs.

cove :
a small indentation or slight recess, usually sheltered, in the shoreline of a sea, lake, or river.

covered berth :
a roofed mooring area that's intended to protect a boat from the effects of sun and weather.

coxswain :
the person, generally a boatswain's mate, who's in charge of steering and/or directing the crew of a boat.

crab :
a maneuver in which a craft is headed partly into the wind to compensate for drift. Also, a mechanical contrivance for hoisting or pulling heavy weights, a truckle.

crash-dive / crash dive :
to dive rapidly at a steep angle, as when a swimmer imitates the emergency maneuver of a submarine or other submersible.

creature feature :
slang for a submerged corpse, typically a gruesome one beginning to suffer the ravages of immersion and marine predation but either insufficiently bloated to float, or one too decomposed for gaseous accumulation, but not yet unrecognizable or skeletal. [nb:the rate of decomposition for a corpse underwater is about half that of one exposed to the open air]

creep :
to grapple; to attempt to seize, hold, grip, or fasten. Also, slang for a grappling iron or grapnel.

crepuscular :
wildlife that becomes active in the dimness of twilight.

crest :
the foamy top of a wave. Also, the point of highest flood, as of a tide.

cringle :
an eye or grommet formed on the boltrope of a sail to permit the attachment of lines; as derived from "circle".

crosshead :
a crosspiece on a rudderpost by which the rudder is turned. Also, a transverse member that's variously employed to transfer alignment or for transmitting energy.

crown :
the part of an anchor at which the arms join the shank; also called "head".

crow's nest :
a lookout platform high atop a ship's main mast, or any observation point with a commanding view.

crush depth :
properly called collapse depth, being the submergence level at which the hull or pressure hull of a vessel suffers catastrophic failure, which is typically well below its design depth; compare maximum operating depth and test depth.

cummerbund :
the waistband for a buoyancy compensator.

cutwater :
the forward edge of the stem of a ship. Also, an upstream face of a bridge pier or piling, sharp edged or sharply pointed, arranged for resisting the effects of moving water or ice.

cyclone :
the word 'cyclone', introduced in 1848 by British meteorologist Henry Piddington, confused "wheel" with "revolve", but has since been accepted as the denotation for the large-scale atmospheric wind-and-pressure system that's characterized by low pressure at its center and by circular wind motion (ie: counterclockwise in the northern hemisphere, clockwise in the southern hemisphere).

cylinder :
the aluminum or steel container that holds pressurized breathing gas for underwater diving; also known as tank or bottle.

Dalton's law :
the principle that the total pressure of a gas mixture is equal to the sum of the partial pressure of its components; or the total pressure exerted by a mixture of gases is the sum of the pressures that would be exerted by each of the gases if it alone were present and occupied the total volume; also called "Dalton's law of partial pressures", "law of partial pressures", and named after John Dalton, the English chemist and physicist.

dam :
an earthen or masonry barrier that's used to obstruct the flow of water, built across a stream or river. Also, a body of water so confined by such a barrier; impoundment, reservoir.

dangly :
anything hanging from a diverís gear that could result in silting or an entanglement hazard, such as exposed knobs, consoles, unsecured straps and lanyards.

dasher block :
a block at the end of a yard or gaff that's used for supporting a signal or ensign halyard; also called "jewel block".

davit :
any of various crane-like devices used on ships for moving or supporting boats, anchors, and other objects.

Davy Jones's locker :
the bottom of the ocean, which serves as a graveyard and junkyard for all that's lost at sea.

abbreviation for decibar, being one tenth of a bar, or approximately a meter of depth in water.

abbreviation for DeCompression Illness.

abbreviation for DeCompression Sickness; also called the bends or aeroembolism.

decompression sickness, a syndrome caused by bubbles of inert gas forming in the tissues and bloodstream during or after ascent from an underwater dive, involving only muscle and joint pain, fatigue, and/or skin irritation (itching, rash).

decompression sickness, a syndrome caused by bubbles of inert gas forming in the tissues and bloodstream during or after ascent from an underwater dive, involving the central nervous system, respiratory system, or circulatory system.

deadhead :
a sunken, semisubmerged, or floating object that's a hazard to navigation.

dead in the water :
adrift without motive, power or propulsion; also called hull.

dead lift :
to raise or move something substantial without mechanical assistance; being any act or exercise requiring a significant effort.

deadlight :
a strong shutter able to be screwed against the interior of a porthole in heavy weather. Also, a thick pane of glass set in the hull or deck to admit light; sometimes called "bull's-eye".

dead-reckoning :
estimated calculation of one's present position based upon compass readings, speed, and distance traveled from the last known point, with allowances for drift from wind or currents; also known as "guesstimate" or "by guess and by God".

dead water :
water eddying beside a moving hull, especially directly astern. Also, a slack current in part of a river or stream.

deadwood :
a solid construction, serving only as reinforcement, located between the keel of a vessel and the stem or sternpost.

dead zone :
that region, both above and below sea level, where existence cannot naturally persist nor be temporarily sustained without life-support supplement or augmentation.

debarkation net :
a specially prepared type of General Purpose net, cargo net, or other similar mesh employed when scaling, as during insertion or extraction, ingress or egress, but especially during debarkation from or embarkation of a transport ship.

deck :
a floor-like surface occupying all or most of one level in a superstructure or hull.

deckhead :
the undersurface of a deck.

deco :
truncation of decompression.

deco mix :
a gas mixture used during decompression, especially nitrox or pure oxygen used to accelerate decompression.

decompression :
the gradual reduction in atmospheric pressure experienced after immersion in deep water or breathing compressed air, resulting in the equalization of gases in body tissues once they have been saturated with nitrogen; staged or continuous change from a higher to a lower ambient pressure always results in a reduction of gas pressure within the body.

decompression buoy :
a small float tethered to a line that, when deployed, will indicate the location of the diver to anyone observing from the surface.

decompression chamber :
a controlled environment for raising and lowering atmospheric pressure with selective air mixtures; also called a hyperbaric chamber.

decompression diving :
a diving practice that goes beyond the standard No-Decompression time/depth limits in order to extend bottom time, which requires one or more decompression stops during ascent regardless of the type of equipment used, since decompression only occurs as the diver ascends; violation of the mandatory in-water stops may result in decompression sickness.

decompression illness :
a diagnosis of dysbaric injuries related to underwater diving, which stem from uncertainty about the mechanistic causation of similar or related neurological symptoms, when the etiology or pathophysiology cannot be determined, and is ultimately immaterial to the treatment regimen. It has been suggested that this diagnosis encompass all manifestations of diseases following a reduction in ambient pressure, such as ascending from a dive.

decompression sickness :
a complex of symptoms caused by the escape of nitrogen bubbles from solution in the fluids that were absorbed originally at higher atmospheric pressure, as a result of the abrupt reduction in that pressure; it is characterized by headache, pain in the arms, legs, joints, and epigastrium, itching of the skin, vertigo, dyspnea, coughing, choking, vomiting, weakness and sometimes paralysis, and severe peripheral circulatory collapse. It is also known as the bends, aeroembolism, caisson disease, and decompression disease.

decompression stop :
the time period that a diver must spend at a constant depth in shallower water after diving at greater depth in order to safely eliminate inert gases from the diver's body so as to avoid decompression sickness.

decompression tables :
cards or booklets printed with index and conversion arrays that allow divers to determine the decompression stops required for a particular dive profile and breathing gas, so as to avoid decompression sickness. Decompression tables assume that the dive is simple and straightforward, an invariable "square dive". These calculations also determine the requisite surface intervals between dives. Also called dive tables or tables.

deep air :
diving to depths greater than 132 feet (40.2m) while using air as the breathing gas; a practice that subjects the diver to nitrogen narcosis or inert gas narcosis, which is seemingly undertaken for its euphoric or narcotic effect.

deep diving :
any dive below the 60 foot (18.2m) depth by sport divers, or below the recreational limit of 132 foot (40.2m) depth by technical divers.

deep six :
to throw or cast overboard while at sea, as when discarding, abandoning, or jettisoning something in more than six fathoms of water; derived from soundings by fathom (6feet), expressed as "by the deep six" (36feet). Also, burial at sea. [nb: refers only to objects; people fall "overboard"]

deep stops :
a method of keeping the diluent gas tension at reasonable levels during a deep dive ascent by introducing more but shorter intervals throughout the series of decompression stops; this methodology of "deep safety stops" was formulated by Richard Pyle, a scientist in Hawaii.

deep water blackout :
usually occurring at a depth of 150ft or more, the diver loses consciousness and ceases all activity while continuing to breathe; the diver stops, remains motionless, and seems to go to sleep.

defogging solution :
a natural (spit) or commercial (artificial compound) liquid that's used as a treatment to prevent condensation on the window of the diver's mask while underwater.

dehydration :
the abnormal depletion of water or other bodily fluids during exertion ... it's an irony to be thirsty while swimming.

deliquesce :
to become liquid by absorbing moisture from the air. Also, to melt away.

Delrin :
brand name of a hard, lightweight, and inflexible polymer that was synthesized from formaldehyde by DuPont in 1952; initially known as "synthetic stone", this material is used in manufacturing cable spools, light housings, belt buckles, knife handles, and the like.

abbreviation for the Dive Equipment and Marketing Association, an organization that sponsors an annual trade show for the introduction, promotion, and display of new products.

demand valve :
a pressure valve, generally placed in the diver's mouth, which provides gas from the diving regulator when the diver inhales; also called mouthpiece.

demersal :
bottom-dwelling marine life that persists at the lowest ocean layers.

depth :
the lowest or deepest point of an underwater dive; the maximum depth reached during the course of a dive.

depth gauge :
a calibrated device, analog or digital, that indicates the distance underwater from the surface (sea level) that the measurement is being taken, as derived from the ambient pressure.

descent / ascent line :
an anchored line, suspended from a boat or buoy, that's used to control a diver's rate of ascent or descent, to provide orientation in strong currents and low light on deep dives, and to secure reserve gas cylinders for decompression stops; a type of safety line that's also called "drop line".

deviation :
the angle of error of a magnetic compass on a given heading as a result of local magnetism; the declination from true north.

diameter indexing safety system :
an Intermediate pressure port where a hose attaches, leading to a demand valve or other apparatus.

diaphragm :
the musculomembranous partition or wall of muscle and connective tissue separating the thoracic cavity from the abdominal cavity, with constriction of this thoraco-abdominal diaphragm being essential for respiration. Also, a flexible semipermeable membrane in a first stage regulator that's used to prevent sea water from contacting the internal parts, which helps to reduce corrosion and contamination.

diel :
pertaining to a 24-hour period, as when referring to the regular daily cycle of an organism's physiology or behavior.

dike / dyke :
an embankment for controlling or holding back the waters of the sea or another body of water. Also, a ditch or causeway. Also, an embankment, barrier, or other obstacle, especially one made from excavated material.

diluent :
a diluting substance, such as oxygen added to nitrogen.

abbreviation for Deutsche Industrie Normen, being the German industrial standards agency, which proliferated criteria worldwide before ISO; later construed as 'Das Ist Norm' for "that is (the) standard"; sometimes (mis-)represented as "Deutsches Institut fuer Normung". The fitting that connects the first stage of a regulator to the compressed air tank on a high pressure scuba system is identified by this DIN standard.

dinghy :
any small boat designed as a tender or lifeboat, whether propelled by rowing or paddling, by sail or motor, as derived from coastal transports for passengers and freight.

DIN valve :
a connection from cylinder to regulator that's identified by its pressure rating (eg: 200 bar or 300 bar).

a mnemonic for "Doing It Right", which is descriptive of a diving style as well as the configuration and maintenance of dive equipment.

dirt dart :
slang for an overloaded diver who has either improperly set his buoyancy control device (BCD), or whose mechanism has failed, causing him to rapidly plunge to the seafloor immediately upon entry into the water; such malfunction is potentially fatal. [cf: picul]

abbreviation for Diameter Indexing Safety System.

distance line :
any braided synthetic cord of small diameter that's used by scuba divers as a means of returning to a safe starting point in underwater conditions of low visibility, or where navigation is difficult (due to water currents or route circuity); also called guideline, safety line, cave line, or penetration line.

ditch :
slang for any body of water that's channeled or confined, such as a river or strait, regardless of size, used informally as a term of convenient reference.

diurnal :
day or daytime; daily or daily cycles; as juxtaposed to nocturnal or seasonal.

diurnal thermocline :
in general, is established each day by heating of the surface water and is destroyed the following night by cooling and/or mixing.

dive club :
a social group organized to enable training, facilitate dive ventures, and promote safe practices, especially recreational scuba diving; sometimes affiliated with a shop or school.

dive computer :
a waterproof electronic device that measures the dive profile and displays related safety information; as the dive computer automatically measures actual depth and elapsed time, it performs a continuous calculation of the partial pressure of gases in the body based on the actual dive profile. A dive computer will address the same problems as decompression tables, but it is also able to warn of excessive ascent rates and missed decompression stops, as well as report the water temperature, and the pressure of the breathing gas remaining in the diving cylinder. A dive computer reduces the need for the diver to carry a separate watch and depth gauge, and relieves the diver of computations, which may be subject to human error.

dive flag :
a public notice to passing watercraft that underwater swimmers are beneath the surface; required to be posted on a mast or buoy, this warning flag exists in two versions: international maritime signal (code letter 'A'), and North American signal (solid red with white diagonal stripe).

dive marshal :
the person responsible for the accountability of students and equipment during training classes; being responsible for recording names, checking equipment, recording water entry and exit times. This safety and security associate functions like a lifeguard, and is sometimes identified as a "beachmaster".

divemaster :
a professional who's qualified to oversee scuba diving operations, as in salvage work or at a school or resort, and is responsible for procedures and safety, monitoring the whereabouts of divers underwater or at the surface, and making rescues whenever necessary.

dive platform :
see sea deck.

dive profile :
a two dimensional graphical representation of a complete dive showing its depth and elapsed time. This profile is often used when describing a dive's probable decompression obligation. It's also known as a depth/time profile, and its coordinate charting is variously configured as square, multilevel, spike, and so forth.

diver down :
common reference to the public notice posted by the dive flag that warns passersby that underwater swimmers are beneath the surface.

Dive Rite :
the first manufacturer (1984) to provide specialized cave and wreck diving equipment.

diver propulsion vehicle :
an underwater transport for divers and equipment that's used to extend travel by increasing their speed of movement.

dive school :
a commercial enterprise offering diving instruction and/or expeditions; sometimes affiliated with a club or shop.

dive shop :
a commercial enterprise offering diving equipment and/or expeditions; sometimes affiliated with a club or school.

dive signal :
the use of fingerspelling, hand language (as in 'command signals'), touch signals, and knock or noise signals that're used to communicate underwater.

dive step / diving step :
see sea deck.

dive tables :
numerical tables used by scuba divers to determine the time limits of dives, according to depth, as well as possible decompression delays during ascent, and the requisite surface intervals between repeat dives; also called decompression tables or tables.

diving bell :
a chamber with an open bottom in which persons can go underwater without special apparatus, water being excluded from the upper part by compressed air fed in by a hose.

diving boat :
a watercraft or other vessel used as a tender for divers or others working under water.

diving mask :
a protective shield worn while under water; also called "face mask", "swim mask", or simply "mask" (qv).

diving reflex :
a physiological reflex of humans, other mammals, reptiles, and birds, that's triggered by immersion in cold water, having the effect of slowing the heart rate and diverting blood flow to the brain, heart, and lungs; serving to conserve oxygen until breathing resumes and to delay potential brain damage.

diving stage :
see stage.

diving suit :
any of various waterproof garments for underwater swimming or diving, especially one that is weighted, hermetically sealed, and supplied with pressurized air.

dock :
a landing pier or wharf. Also, the space or waterway between two piers or wharves, as for receiving a ship while in port. Also, such a waterway, enclosed or open, together with the surrounding piers, wharves, and other structures. Also, a dry dock.

dodger :
an overhead canvas top with front and side panels that's supported on scantling for protection against windblown rain, snow, or spray; also known as a spray-hood, an extension may be added to enclose the aft opening of the dodger.

acronym for Dead Object Drifting Obstacle (or "Dead Or Drifting Object") indicating inert debris or incidental hazards to navigation; since such flotsam is not underway, the craft or vessel must maneuver to avoid collision damage.

dog paddle :
the most basic or rudimentary swimming stroke, typically performed in a crouching posture with both arms and legs fluttering beneath the surface while the head is held above the surface of the water; performed by imitation, and so-called by comparison. [v: crawl, breaststroke, sidestroke, trudgen, butterfly, backstroke]

dolphin :
any small toothed cetacean, especially one possessed of a beaklike snout; compare porpoise. Also, a buoy, pile, or cluster of piles used as a fender or mooring. Also, a rope or strap round a mast to support the puddening, where the lower yards rest in the slings.

Doppler ultrasound bubble detector :
a diagnostic device used in hyperbaric medicine to determine the presence (by Doppler shift) of bubbles in the bloodstream that may presage decompression sickness.

double berth :
a mooring that accommodates two boats, with a finger pier on only one side of each berthed vessel.

doubles :
two back-mounted air cylinders banded together and connected by a manifold so as to allow longer dive time and redundant gas; used instead of a single air cylinder.

downstream valve :
a second stage design wherein the gas flow is always positive, flowing outward from the regulator, such that in the event of a failure, it will fail free-flow leaking, not shut off.

abbreviation for Diver Propulsion Vehicle; sometimes called a "scooter", as used to quickly traverse long distances underwater.

Draeger :
with reference to the closed-circuit oxygen re-breather, invented (together with other rescue equipment) by Alexander B. Dräger, an early 20th century German scientist.

Draeger tube :
an indicator used to test the quality of a breathing gas.

draft :
the depth to which a vessel is immersed when bearing a given load.

dragrope :
a rope that's been attached to something and is then used to drag or haul it. Also, the end of a rope that's hanging loose or trailing behind its point of attachment; a trawl.

drainage basin :
the area drained by a river and all its tributaries; also called a "catchment area" or "drainage area".

drift dive :
a dive in which the divers drift with the current, and the dive boat follows the surface marker buoy (SMB) towed by the freely drifting divers.

D-ring :
a metal ring in the shape of a capital letter 'D' that's used on the harness for attaching items by clipping onto them; chest mounted D-rings are often bent outward to aid in the clipping process.

drogue :
a bucket or canvas bag used as a vessel's "sea anchor", causing resistance to movement of the hull through the water, so as to decrease speed and/or increase stability.

drop line :
an anchored line, suspended from a boat or buoy, that's used to control a diver's rate of ascent or descent, to provide orientation in low light on deep dives, and to secure reserve gas cylinders for decompression stops; a type of safety line that's also called "ascent / descent line".

drown :
to suffocate by aspirating liquid. Also, to be inundated or overwhelmed.

droxtal :
a tiny ice particle, formed by direct freezing of supercooled water droplets with little growth directly from the vapor, causing most of the visibility reduction in ice fog; the term derives from a combination of the words drop and crystal.

dryback / dry back :
slang for a sailor who has not served aboard a ship at sea, especially someone who has not experienced naval warfare; being someone who has not gotten "wet" or been "wetted down".

dry bag :
a collapsible watertight container used for carrying clothes, gear, and artifacts; it will float if not overloaded.

dry dock :
a structure able to contain an entire ship, leaving all parts of the hull accessible for construction or maintenance.

dry suit / drysuit :
a close-fitting, double-layered, watertight synthetic garment worn by a deep-sea diver in very cold environments, usually with thermal underwear, that's designed to protect the diver's body from the water or pressure by circulating a warm insulating layer of air internally, which also serves to equalize descent pressures.

dual regulator system :
a reserve regulator that's already situated in series with the primary, so as to enable an uninterrupted air flow; the use of two regulators on a single air supply.

dump station :
a facility located in a marina, on docks or on shore, that's specifically designed to receive sewage from the portable toilets and holding tanks carried aboard vessels.

durometer :
an apparatus for measuring the Shore hardness of rubber or plastic, which value is determined by the depth of penetration of the durometer indenter foot into the specimen material; due to the resilience of these materials, the indentation recovery time is sometimes reported along with the hardness reading (eg: ASTM D2240 00).

Dutchman's breeches :
the opening of two patches of blue in an otherwise stormy sky, giving the promise of better weather; being a fancied allusion to making a pair of short trousers (knickers or knickerbockers) with small bits of clear sky.

Dutchman's log :
a rough method of gauging the speed of a vessel by measuring the elapsed time for a float to travel from an observation point at the bow to an observation point at the stern, using the known shipboard distance and the realized time to calculate the rate.

dyne :
the standard centimeter-gram-second unit of force, equal to the force that produces an acceleration of one centimeter per second per second on a mass of one gram. [nb: 1000 dynes = 1 millibar, 1 millibar = 1/1000 bar]

dysbarism :
medical conditions resulting from changes in ambient pressure.

abbreviation for Equivalent Air Depth, being a conversion of nitrox to air, so that air tables can be used for dive planning.

abbreviation for Enriched-Air Nitrox, which may be used with numeric values to identify the specific oxygen content of a gas (eg: EAN32); also represented as EANx.

easy :
formed in a long curve, so as to make a gradual transition between the bottom and sides of a vessel; or having gently curved surfaces leading from the middle body to the stern of a vessel, as of the run of a hull; not abrupt; slack.

ebb tide :
the reflux of tide or the outflow of falling water from the tidal current; as opposed to flood tide.

eddy :
a counter current running at variance with the main current in a stream or other body, especially one having a rotary or whirling motion (such as a small whirlpool).

electro-galvanic fuel cell :
an electrical device used to measure the concentration of oxygen in the breathing gas loop of fully closed-circuit re-breather systems so as to detect and adjust the partial pressure mixture; a ppO2 meter / ppO2 meter.

embarcadero :
a pier or wharf, especially a waterfront section that's been commercially developed.

enriched-air nitrox :
a breathing gas that contains more oxygen than normal air and a corresponding decrease in the amount of nitrogen; an air mix containing more than 21 percent oxygen, usually made by mixing air and oxygen; abbreviated EAN or EANx.

a perflourinated material that's resistant to oxygen erosion, as used to make O-rings.

epilimnion :
the layer of water above the thermocline, being that overlying region of a thermally stratified lake or reservoir in which there is a rapid decrease in temperature with water depth.

Emergency Position-Indicating Radio Beacon, being a global maritime distress and safety broadcast device that's required by Coast Guard boating regulations; a signal device, usually carried aboard maritime craft, that when activated in an emergency will broadcast its location to search aircraft and orbital satellites to enable rescue.

equalization :
the forcing of air into an open space (eg: dive mask) or cavity (eg: middle ear) so as to attain balance or to offset increasing hydrostatic pressure; used to prevent a "squeeze".

equatorial tide :
a semimonthly tide that appears when the moon is over the equator.

equatorial trough :
the quasi-continuous belt of low atmospheric pressure that lies between the subtropical high-pressure belts of the northern and southern hemispheres.

equivalent air depth :
the underwater depth at which air would cause as much decompression obligation as nitrogen (eg: nitrox, trimix) with a given O2 concentration.

erythropoiesis :
the making of red blood cells.

erythropoietin :
a hormone that stimulates production of red blood cells and hemoglobin in the bone marrow.

esplanade :
an open level space, especially one serving for public access along a shore.

estuary :
that part of the lower course (mouth) of a river in which the river's current meets the sea's tide. Also, an arm or inlet of the sea at the lower end of a river.

eurybathic :
freshwater or marine life that can tolerate a wide range of depths; as opposed to stenobathic.

eustachian tube :
a canal extending from the middle ear to the pharynx; eponymously after Bartolommeo Eustachio, an Italian anatomist. By permitting air to leave or enter the middle ear, this tube equalizes air pressure on either side of the eardrum.

even keel :
when the fore and aft draft of a vessel is the same on both sides; floating level at the waterline.

exhaust valve :
a one-way or non-return valve that's incorporated into the exhaust hose to keep the exhaled air flowing in the proper direction, and prevent excessive back pressure.

exposure protection :
any garment worn to prevent bodily injury from temperature, abrasion, contamination, or predation; may be augmented by insulators, repellents, and other aids.

exposure suit :
a garment worn by divers for thermal protection. Also, a high visibility insulated garment worn while working topside when unprotected immersion may be life-threatening; this survival coverall is sometimes called a "pumpkin suit" due to its color.

eye of the storm :
an area of low pressure in the centre of a tornado; an opening in storm clouds that's relatively calm.

eye of the wind :
in nautical parlance, the direction from which the wind is blowing.

face mask :
a protective shield worn while under water; also called "swim mask", "diving mask", or simply "mask" (qv).

fahrenheit :
a temperature scale in which 32 represents the freeze point and 212 represents the boiling point. [nb: the degree intervals of the kelvin scale are the same as celsius, as the rankine are the same as fahrenheit]

fairlead :
a rigging guide or fitting for pulley, thimble, block, or CAPSTAN which prevents chafing of the line.

fairwater :
a hydrodynamic structure on a ship designed to direct or deflect the flow of water; being the modern name for the conning tower of a submarine.

fairway :
an unobstructed passage or area, being the navigable portion of a waterway.

fall :
the part of the rope of a tackle to which the power is applied in hoisting. Also, the flap opening at the front of some types of men's trousers.

fantail :
the open area near the stern of a vessel, which may have bulwarks; also called the afterdeck.

fast :
made or held secure, as firmly fixed in place. Also, firmly tied, as a knot. Also, closed and made secure, as a hatch or cover, door or shutter. Also, close or near.

fast ice :
ice that is grounded on or attached to the bottom of an area covered by shallow water.

fathom :
a nautical unit of length equal to 6 feet (1.8 m); as derived from "span of arms" or embrace. Also, to measure depth by means of a sounding line; to sound.

Fathometer :
the trademarked brand name of a sonic depth finder; often used generically.

abbreviation for the Federation of Australian Underwater Instructors.

favonian :
mild or favorable; propitious, by reference or allusion to the west wind.

fender :
any shield or cushion, buffer or bumper that's hung over the side of a vessel to lessen shock or to prevent hull chafing, such as a balk of timber, a bundle of rope, a rubber tire, or the like; derived by shortening from defender, as a guard.

fetch :
an area where ocean waves are being generated by the wind. Also, to move or maneuver nautically; to arrive or reach by water.

abbreviation for Foot/Feet of Fresh Water, a depth measurement.

fid :
a long, smooth, tapered, wooden tool used to open the strands of a rope or line for splicing.

fiddlehead :
a billethead (or scrollhead) having a form similar to the volute carved at the upper end of a violin.

figurehead :
a carved bust or full-length figure that's built into the bow of a sailing ship.

fin :
a horizontal winglike appendage to the underwater portion of a hull, often adjustable, as the planes for controlling the dive of a submarine, or the fin keel for damping the roll of a surface vessel. Also, slang for one of a pair of paddlelike devices, usually made of rubber, that are worn on the feet as an aid in swimming and underwater diving; imitative of the broad flat limbs or the membranous organs of aquatic animals that are used for steering and propulsion; also called swimfin or flipper. Also, slang for the human hand.

finger float :
an access walkway that defines the size of a berth; also known as a finger pier, so called from its finger-like resemblance. [v: phalanx, phalange]

finger pier :
a structural extension from a dock that's delineated for the berthing or mooring of vessels (or other watercraft) for the purpose of embarking or disembarking, and for wet storage; also known as finger float.

first stage :
the initial phase of pressure reduction by the regulator assembly, set to deliver intermediate air pressure from the high pressure air cylinder to the second stage of the regulator.

firth :
a long, narrow indentation of the seacoast; also represented as "frith".

fjord :
a long, narrow arm of the sea, bordered by steep cliffs, that's usually formed by glacial erosion; also represented as "fiord". Also, in Scandinavia, a bay.

flagella :
a long lash-like appendage that serves as an organ of locomotion in protozoa, algae, sperm cells, and other microorganisms. [v: dinoflagellate]

flagship :
the primary or principal vessel of a group or line; typically the best or most important one, as the headquarters ship or boat with the superior crew.

flank speed :
the maximum possible speed of a ship; in the progression of prescribed standard speeds, an increase faster than full speed. [v: amain]

flip-flop entry :
see backward roll entry.

flipper :
slang for one of a pair of paddlelike devices, usually made of rubber, that are worn on the feet as an aid in swimming and scuba diving; imitative of the broad flat limbs or the membranous organs of aquatic animals that are used for steering and propulsion; also called fin or swimfin. Also, slang for the human hand.

float :
something that floats or something for buoying up, being a hollow object, inflated container, or buoyant material that tends to remain at, or to return to the surface of water, such as a pontoon or raft, water wings or life preserver. Also, an inflated bag to sustain a person in water; a life preserver. Also, a floating platform that's attached to a wharf, bank, or the like, and is used as a landing. Also, a hollow, boat-like structure under the wing or fuselage of a seaplane or flying boat, keeping it afloat in water; also called a pontoon. Also, slang for a tour aboard ship at sea; being a cruise out from port and back. Also, an unspecified number of ships operating together in the same area as a single or unified group.

floater :
slang for a corpse that's risen by bloat to the surface; once gases pass off (usually by venting during predation), the corpse again sinks to the seafloor. [nb:the rate of decomposition for a corpse underwater is about half that of one exposed to the open air]

floating garage / floating tender garage :
a hollow interior within the hull of a ship or within the chamber of a moored platform, that admits surface vessels through a water-tight opening (shell door) situated at sea level; this configuration obviates the need for a boarding ladder or an elevating hoist.

floe :
a sheet of floating ice, or a detached portion thereof, chiefly on the surface of the sea that's smaller than an ice field; also called ice floe, as derived from "layer".

floeberg :
a mass of ice floes resembling an iceberg.

flood :
to fill a space with water. Also, a rising tide; an elevation in sea level.

flood tide :
the inflow of rising water from the tidal current; as opposed to ebb tide.

flotsam :
wreckage or refuse found floating on water; as derived from "float".

flow meter :
a visual indicator that displays the rate at which a gas (or fluid) is flowing, as in a re-breather or oxygen analyzer.

flow restrictor :
a device inserted into a flow line to fractionally limit the volume of gas so that variations in pressure cannot affect sensor metering.

flowstone :
a layered deposit of calcium carbonate that's been left by thin sheets of flowing water, as in a cave.

fluke :
the retentive part of an anchor that catches in the seafloor, especially the flat triangular piece at the end of each arm. Also, the barbed head of a harpoon, spear, arrow, or the like. Also, a stroke of good luck or a chance happening; an accidentally successful act or event.

flume :
a deep narrow defile containing a mountain stream or torrent. Also, an artificial channel or trough used for conducting water.

flying bridge :
a small open deck, situated above the main cabin or pilothouse of a vessel, having duplicate navigational equipment and bridge controls; also called "bridge deck" or "monkey island".

flying boat :
a high-winged passenger / cargo aircraft with a boat-bottomed hull and two- or four-engines that operates from the surface of the water.

flying gangway :
a raised fore-and-aft catwalk permitting safe passage when the weather deck of a ship is washed by heavy seas; also called "monkey bridge".

following sea :
an overtaking current that approaches a vessel from its stern.

footie :
a waterproof (neoprene) sock-like foot covering, serving to insulate and protect the diver's foot and ankle, that's worn inside open-heeled flippers or fins; also called "bootie" or "bootee".

forecastle :
(fohk-suhl) the part of the weather deck forward of the foremast, which may have bulwarks. Also, a superstructure at or immediately aft of the bow or prow of a vessel, that's used as a shelter for stores and machinery, or as quarters for sailors.

forecastle deck :
a partial weather deck on top of a forecastle superstructure; also called a topgallant forecastle.

forecastle head :
the extreme fore part of a forecastle superstructure. Also, the extreme fore part of the main weather deck of a vessel that has no forecastle superstructure.

forward roll entry :
a self-protective water entry method in which the fully equipped standing diver bends forward from the waist into a body tuck from a pier, deck, or other platform elevated not more than 7ft (2m) above sea level, with face mask held in place, allowing the back-mounted air tank to strike the water surface first, and then continues the partial somersault underwater into a prone swimming position; any extra gear or bottles ride in the diver's protected "breadbasket" for a safe and secure entry. This method is used when either the giant stride entry or backward roll entry methods would not be suitable.

foul :
that which is clogged or obstructed with foreign matter. Also, stormy or inclement, as foul conditions that impede navigation. Also, obstructed or entangled, as a foul anchor. Also, a collision, to collide; as derived from "to stink".

founder :
the wrecking or sinking of a vessel.

fountainhead :
the origin or source, as the spring from which a stream flows.

freak wave :
an abnormally large wave that occurs on a seemingly random basis in the oceans; this unpredictable sea wave is also known as a rogue wave, sleeper wave, sneaker wave, and king wave. Of enormous proportion, great in height and steepness, these unexpected waves sometimes travel in a direction at an angle to the prevailing seas, or occur where waves meet opposing currents.

freeboard :
the portion of the side of a vessel's hull that's above the water; in particular, the distance between the uppermost fully watertight deck and the demarcated official load-line. Also, the vertical distance from the water surface to the top of the deck of a vessel or dock.

freeboard deck :
the uppermost deck on a cargo vessel that's officially considered to be watertight: also called upper deck, it's used as the level from which the plimsoll marks are measured.

free diving / free-diving :
underwater diving without supplemental air or breathing equipment; also called breath-hold diving or skin diving.

freeing port :
an opening in the bottom of a bulwark used for the rapid drainage of a weather deck in heavy seas; a type of scupper.

freshet :
the sudden rise in the level of a stream, or a flooding that's caused by heavy rains or by the rapid melting of snow and ice. Also, a freshwater stream that flows into the sea.

frogman :
nickname for a scuba diver, especially one on a military mission.

abbreviation for Foot/Feet of Sea Water, a depth measurement.

fuel dock :
a dedicated structure, or a delineated area on a larger structure (ie: pier, dock, bulkhead, etc), that is specifically used for the dispensing of boat fuel; also called "marine service station", "fuel dispensing facility", or "fueling station".

Fujita scale :
a scale indicating the speed or force of cyclonic wind, as that of a tornado or waterspout.

full face mask :
a protective shield worn while under water, often with an insulating hood, so as to safeguard the diver against exposure to cold temperatures or other extremes.

full fathom five :
an alliterative allusion to an underwater depth of thirty feet, or approximately one atmosphere of pressure (that is, double the pressure at sea level), which was once a formidable barrier for breath-hold diving. Also, a poetic expression meaning a full change or a complete alteration that's beyond human control or influence; a total transformation.

gaff :
a metallic hook attached to a long handle that's used for landing large fish, or for fishing objects from the water. Also, a spar rising aft from a mast, primarily used to support the head of a quadrilateral fore-and-aft sail (gaff sail).

gaiter :
a lower leg covering for a dry suit, which wrap is used to restrict or constrict that airspace so as to help maintain body position and buoyancy control; a "squeezer" added to improve trim on deep dives.

gale :
a very strong wind; properly, a wind of 32-63mph, as measured on the Saffir-Simpson scale.

galvanic corrosion :
a phenomenon that occurs when disparate metals contact one another, which deterioration may be slow or fast, depending upon the level of acidity or alkalinity, and is augmented by the addition of sea water. [cf: voltaic pile]

galvanize / galvanization :
an electrochemical technique for coating metal, especially iron or steel, with a protective layer of zinc as a preservative against decomposition.

gangplank :
a narrow plank, often inclined with transverse traction cleats, that's used as a temporary bridge onto a vessel; a brow serving as a walkway or passageway.

gangway :
a narrow walkway or passageway. Also, an opening in the railing or bulwark of a vessel for use as a passageway. Also, a temporary bridge at the opening in the railing or bulwark of a vessel; also known as a brow or gangplank.

gantline :
a rope rove through a single block that's hung from a spar, mast, funnel, or other stanchion, used as a means of hoisting workers, tools, flags, or the like; as derived from earlier "girtline", being a line for girding.

gasoline alley :
an aisle, corridor, passageway, or gangway connecting the bulkheads of several fuel storage and engine compartments in the bowels of a ship.

gasp reflex :
an involuntary physiological response to suddenly plunging into very cold water (50°F or less), which automatic reaction contributes to hypothermia and drowning; the human body cannot be habituated to such shocking immersion ... only somewhat accommodated by protective preparation.

gat :
a passage or channel that extends inland from a shore; derived from "hole" or "opening".

gauge pressure :
a measure of pressure that doesn't include the effect of the atmosphere, such as a submersible pressure gauge (SPG).

Gay-Lussac's law :
the principle that, for relatively low pressures, the density of an ideal gas at constant pressure varies inversely with the absolute temperature of the gas; also called Charles' law, and named after Joseph Louis Gay-Lussac, a French chemist and physicist.

Gel Cell :
brand name of a sealed lead-acid battery pack that will function in any position without spilling or leaking, as used with canister lights.

giant stride entry :
the most common water entry method in which the fully equipped standing diver takes a long step from a pier, deck, or other platform into the water, with chin tucked and mask securely held, and then immediately closes legs together in a scissor-kick as soon as the water surface has been broken, to stay shallow and remain upright for a quick check of equipment before making a controlled descent; also called "spread-eagle" jump and "lifesaving" leap. Any extra gear and bottles are either held in the hands or are lowered separately on ropes.

gig :
a small lightweight boat propelled by long oars, as a scull or dinghy. Also, a long, thick-handled fork with barbed tines that's used to spear fish and frogs; derived by shortening of 'fishgig' and 'fizgig'. Also, a device that commonly consists of four hooks secured back-to-back, which is used to drag through a school of fish so as to hook them through the body.

giggles 'n' bangs :
slang for the hull noise, from creaks and groans to thumps and pops, induced by the effects of high pressure at greater depths on submerged vessels.

gimlet / gimblet :
to rotate a suspended anchor to a desired position.

glory hole :
the quarters on a ship that are occupied by the stewards or stokers. Also, a small storeroom within the hull of a ship, usually at the stern; also called "lazaretto". Also, an enclosed space or locker for stowing loose gear. Also, a place for concealing valuables, a cache hideaway or treasure trove.

goat locker :
the Chief Petty Officer's quarters aboard a submarine; derived from the space where a milch goat was kept aboard sailing ships.

goggles :
large spectacles furnished with special lenses and reinforced rims for the protection of the eyes from injury.

Gold Line :
brand name of a vivid yellow nylon rope (kernmantle), durable and resilient, that's pre-positioned as a perpetual guideline in caves that are regularly visited by tourists.

gore :
a triangular piece of material inserted in a garment, sail, or the like, to give it greater width or a desired shape. [cf: godet, gusset] Also, one of the panels, usually tapering or shaped, making up a garment or other fabric construction.

goring :
the triangular area along a leech of a square sail, created by the presence of a gore.

gox :
abbreviation for gaseous oxygen.

abbreviation for Global Positioning System, being a satellite based method of triangulation used during navigation; high-tech successor to sextant.

gradient :
the rate of change with respect to distance of a variable quantity, as temperature or pressure, in the direction of maximum change; used as a vector of angle during ascent or descend.

granny line :
a line which goes from the stern platform or transom to the anchor line; also called "gerry line".

grapnel :
a device consisting of one or more hooks or clamps that's used for holding or grasping; also called a "grapple", "grappling iron", "gang hook", or "creep". Also, a small anchor or anchor-like device with three or more flukes that's used for grappling or dragging; as derived from "grape hook".

grapple :
to hold or make fast to something, as with a grapnel or grappling iron, a gang hook or creep; to seize or fasten. Also, to struggle or wrestle with something, such as a problem or an obstacle.

green flash :
a green coloration, caused by atmospheric refraction of the upper portion of the sun, that's occasionally seen as the sun rises above or sinks below the horizon; also known as "Neptune's wink" when observed at sea, and "zodiacal light" for its occurrence in a narrow band called the 'zodiac' or plane of the ecliptic.

green water :
sea water that doesn't break up into spray or spume, especially the solid swell or wave that washes aboard a vessel.

grot-hole :
a colloquialism for a small insignificant cave with no further leads, usually tight and difficult to manoeuvre.

grotto :
a cave or cavern; a subterranean chamber. Also, an artificial cavern-like recess.

groundswell :
a broad, deep swell or rolling of the sea, due to a distant storm or gale.

groundwater :
water in a below ground aquifer that flows from high to low areas except when a pressure gradient causes the water to move against gravity, at a speed related to the magnitude of the pressure gradient and the permeability of the aquifer. Groundwater intersects surface water through springs, streams, rivers, lakes, swamps, and other features.

growler :
a small iceberg, but one large enough to be a navigational hazard.

groyne / groin :
a small jetty extending from a shore to prevent beach erosion.

guard rail :
a railing system, including a top rail, located along the edge of a walkway, gangway, passageway, stairway, or other transit surface so as to minimize the possibility of an accidental fall; also called handrail or safety rail.

guess-warp :
a rope fastened to a vessel or wharf, and used to tow or haul a boat or vessel into place; also called "guess-rope".

guideline :
an emplaced rope or cord that serves to direct someone's passage over unfamiliar terrain; a safety line laid temporarily through an entanglement or maze that marks the route and establishes the entrance, which is retrieved by the last diver when exiting.

guide pile :
a pile that holds a floating dock on location, and allows the dock to rise and fall with changing water levels.

gulf :
a portion of an ocean or sea that's partly enclosed by land. Also, a deep hollow, as a chasm or abyss. Also, any great or wide separation. Also, something that engulfs or swallows up.

gunk hole :
a quiet anchorage, as in a cove, used by small yachts.

gunnel :
see gunwale.

gun tackle :
a tackle composed of a fall rove through two single blocks and secured to one of them so as to secure a mechanical advantage of two or three, neglecting friction, depending on the arrangement.

gunwale :
the upper edge of the side or bulwark of a vessel; also represented as "gunnel". Also, the sheer strake of a wooden vessel; the uppermost strake beneath the plank-sheer.

gut :
a narrow passage, as a channel of water. Also, to remove the vital or essential parts from something.

guts :
from the abdomen or bowels, fortitude and determination. Also, the inner working parts of a device or mechanism.

gypsyhead :
a flanged drum on a winch that's used for winding in lines.

gyre :
a ring-like system of ocean currents rotating clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. Also, any circular course or motion; as derived from 'ring'.

hadal :
pertaining to the biogeographic region of the ocean bottom below the abyssal zone; below approximately 20,000 feet, being the greatest ocean depths.

Haldanean / Haldanian :
a relative theory by John Scott Haldane that nitrogen is taken up and given off in exponential fashion during a dive, and that there is some safe ratio of pressure change for ascent; decompression models of tissue saturation and desaturation based on the principles (eg: critical ratio hypothesis) described by J.S. Haldane.

half deck :
the portion of the deck below the upper or spar deck, and aft of the mainmast on a sailing ship.

half-time :
the time required for body tissue to absorb or release half of the total gas required to reach equilibrium with the surrounding gas pressure.

halocline :
a well-defined vertical salinity gradient in ocean or other saline water; a visible boundary, like a barrier of mist, between layers of water of different salinities.

halyard :
any of various lines or tackles for hoisting a flag, sail, spar, or other object into position.

handy :
term of approbation for capable seamen or skillful sailors who are dexterous and adroit, deft and nimble; not lubberly. Also, a craft or vessel that is easily maneuvered, responsive to controls.

hang :
slang for a diver remaining stationary at a particular depth or location for a specific time, especially when performing a staged decompression.

hang tank :
an extra air tank of breathing gas that's staged on the ascent line at the decompression stop.

harbor :
a natural or artificial part of a body of water, situated along the shore or coast, that's deep enough to anchor a ship and provide protection against winds, waves, and currents; often having docks or other port facilities. Also, any place of shelter or refuge, a haven or retreat, an asylum or sanctuary, such as a cold harbor.

hard-and-fast :
a ship run aground. Also, something unalterable.

hard hat :
the helmet used with a dry suit during underwater construction and salvage diving; the two-part helmet (bonnet and corselet) includes viewing ports and connectors for air and communication lines.

hard suit :
slang for the Atmospheric Diving Suit, being an articulated self-contained hard-shell protective body covering for deep underwater explorations (2000' max 6hrs).

harness :
an arrangement of webbing straps with quick release buckles that's worn by a diver for attaching the buoyancy compensator, backplate, air tanks, and any peripheral apparatus or gear.

harpoon :
a spear-like missile, barbed with a tethering line attached, that's thrown or shot so as to spear fish or other sea life.

hatch :
an opening in the DECK of a vessel used as a passageway, or the cover over such an opening; also called a "hatchway" (not a "watertight door" in a BULKHEAD).

hawsepipe :
an iron or steel pipe situated in the stem or bow of a vessel through which an anchor cable passes.

hawser :
a heavy cable used for mooring or towing [nb: this line is never called a 'rope'].

head :
a toilet or lavatory on a boat or ship. Also, the forepart of a vessel; its bow or stem. Also, the part of an anchor at which the arms join the shank; also called "crown". Also, the upper edge of a quadrilateral sail, or the upper corner of a jib-headed sail.

heading :
the course or direction of travel for a person, party, or vessel. Also, the angle between the axis of a vessel and some reference line.

head sea :
a formation of waves running in a direction opposite to that of a vessel.

headway :
forward movement, advancement, or progress. Also, the interval of time or distance, relative to the situation or circumstances, between two vessels traveling in the same direction over the same route. [cf: forereach]

heave :
to lift or hoist. Also, to forceably throw something, especially a weighted line (eg: heaving line). Also, to pull or haul on a rope, line, cable, or the like. Also, the rise and fall of the waves or swell of a sea. Also, the vertical rise and fall of a craft or vessel. Also, to halt or stop the advance of a craft or vessel ("heave to") by causing it to lose headway. Also, to move in a certain direction or into a certain position or situation, as "the ship hove into sight". Also, to vomit, retch, keck, regurgitate, throw-up, upchuck, barf, toss cookies, ralph, disgorge, nausea, mal de mer, or puke.

heave-ho :
an exclamatory call or chant used by sailors when hauling or working, especially used to signal that the anchor's aweigh.

heaving line :
a light or thin cord or rope, with its trailing end weighted by a knot, that's used to toss overboard to a swimmer or small boat, or to a wharf or mole, or between vessels for transferring larger cables; also known as a "messenger line" or "throw line".

heliair :
a blended breathing gas consisting of a mixture of oxygen, nitrogen, and helium, that's often used during the deep phase of dives using Technical diving techniques. The helium and air blend has a 21:79 ratio of oxygen and nitrogen.

heliox :
a blended breathing gas consisting of a mixture of oxygen and helium, that is often used during the deep phase of dives using technical diving techniques. Since sound travels faster in heliox than in air, voice formants are raised, making divers' speech incomprehensible to people not accustomed to it. Being more expensive, its use is often limited to commercial dives.

helium :
an inert, colorless, odorless, tasteless chemical element, which exists, except in extreme conditions, only as a gas. It is not toxic and has no known biological effect. It is the second most abundant element in the universe, with its boiling and melting points among the lowest of the elements; significant amounts are found on earth only in natural gas. Helium is used in cryogenics, in deep-sea breathing systems, for inflating balloons, and as a protective gas for many purposes. Because helium does not create problems with narcosis to the same extent as nitrogen, it's therefore used for very deep diving.

helm :
the steering apparatus, as a wheel or tiller, by which a vessel is navigated. Also, the point, position, or location of control. [nb: where the ship's steering wheel has been replaced by levers or joysticks for controlling propulsion pods and thrusters, the helm is called an "integrated bridge system workstation"]

Henry's law :
the principle that the amount of a gas that dissolves in a liquid is proportional to the partial pressure of the gas over the liquid, provided that no chemical reaction takes place between the liquid and the gas; or the amount of gas that will dissolve in a liquid at a given temperature is almost directly proportional to the partial pressure of that gas; as devised by William Henry, an English chemist.

Hg :
the chemical symbol for mercury [hydrargyrum: liquid silver; by analogy with aurum, argentum, etc].

abbreviation for High Intensity Discharge, being a technology that generates high intensity white-blue lighting underwater with very low battery power.

high pressure cylinder :
steel air cylinders that're used at fill pressures of 3,500 psi (230 bar).

high seas :
the open sea or ocean that's beyond the limit of a country's territorial waters; also called "international waters".

Hogarthian / Hogarthian configuration :
a minimalistic arrangement of streamlined equipment that's intended to maximize gas efficiency for extended cave diving, including enough redundancy for decompression stops; as advocated by William Hogarth Main, a Florida cave diver. [v: ultralight]

hogging :
the behavior of a ship when only its midships area is supported by the crest of a wave, leaving the bow and stern unsupported by troughs.

hoise :
to hoist, haul, or rouse, to pull together, as derived from "hissa" and "huzzah" work chants.

hoist :
any lifting apparatus, such as tackle or boom; derived from hoise.

hold :
the cargo space in the hull of a vessel, especially between the lowermost deck and the bottom. Also, any individual compartment or bay of a larger cargo space that's closed by bulkheads and has its own hatch or hatchway; as a variant derived from hole.

holdfast :
something used to hold or secure a thing in place.

holding tank :
any retention system (eg: Type III Marine Sanitation Device) on-board a vessel that functions by receiving and holding sewage, which is periodically emptied at approved pumpout sites or dump stations, or discharge beyond the 3 mile offshore limit (except within federally designated No-Discharge Areas).

holiday diver :
someone who engages in underwater swimming while on vacation, as an excursion or expedition, but rarely dives when close to home; also called "leisure diver" or "tourist". [nb: many holiday divers do not venture below the 33 foot depth of one standard atmosphere, and most do not venture below the 90 foot depth of two atmospheres, due to the need for mixed breathing gases, decompression stops, and technical training]

hollow sea :
an ocean wave formation in which the rise from troughs to crests is very steep.

hood :
a garment worn over the head (and neck) as thermal insulation or impact protection; it's often accompanied by a full face mask. [cf: balaclava, coif, pileus/pîlos]

hook :
slang for an anchor of any style, also called "killick", as used as a retainer or brake.

hookah :
surface-supplied compressed air apparatus that's used by several divers in series during shallow dives in calm waters; the air is delivered to the divers through a long hose.

horsecollar :
slang for the old style floatation device worn around the neck, known as the adjustable buoyancy lifejacket (ABLJ), replaced by the buoyancy compensator (BC) or buoyancy control device (BCD).

hovercraft :
a passenger vehicle that rides on a cushion of air, that's kept aloft by fans and driven forward by propellers; trademarked name for an air-cushioned vehicle (ACV).

Hovering Act :
an international law that restricts or forbids the loitering of vessels (foreign or domestic) within the prescribed limits of a coastal nation; this act stipulates that foreign vessels may be boarded, and their shipping manifests checked by the appropriate government officials, when beyond the three-mile limit of a coastal nation.

HP :
abbreviation for high pressure.

HP hose :
the high pressure hose that connects the first stage of the regulator to the air pressure gauge; a hose designed to accept high pressure cylinder gas without rupturing.

High-Pressure Nervous Syndrome, being a secondary reaction caused by the use at depth of breathing gases containing helium; also called "helium tremors".

Hyperbaric Rescue Craft; a self-contained, self-propelled escape module used by saturation divers when weather or other emergency conditions jeopardize their life-support.

abbreviation for Handicapped Scuba Association International.

hull :
the outermost and lowermost hollow portion of a ship or other vessel, together with its framework support structure, that floats partially submerged while supporting its infrastructure and superstructure; the "shell" or "skin" of a boat or amphibious craft enabling it to float. [nb: the hull on European ships bears a resemblance to fish, while the hull on Asian junks bears a resemblance to waterfowl] Also, to drift, as a ship or other craft, without power or propulsion; also called "dead in the water".

hurricane :
a violent cyclonic storm, occurring especially in the northwestern and midwestern Atlantic and its tropical inlands, having wind speeds of or in excess of 74mph, as measured on the Saffir-Simpson scale; derived from "Hurakan", the name of the Caribbean Indian storm god.

hurricane deck / hurricane-deck :
a deck at the top of a passenger steamer, having a roof supported by light scantlings; also called "awning deck" or "shade deck".

H-valve :
a single cylinder tank valve with two outlets that provides for dual regulators.

abbreviation for High Water Level.

hydrodynamics :
the branch of fluid dynamics that deals with liquids; the science dealing with the laws governing water or other liquids in motion.

hydrofoil :
a winglike surface form that creates perpendicular thrust against water so as to lift a vessel to which these members are attached while that vessel is moving. Also, a vessel with such members attached.

hydrogen :
a colorless, odorless, flammable gas, being the lightest and most abundant of the elements; It has been proposed as a substitute for helium in deep commercial and military diving.

hydrogeology :
the science dealing with the occurrence and distribution of underground water.

hydrography :
the science of the measurement, description, and mapping of the surface waters of the earth, especially pertaining to navigation.

hydrology :
the science dealing with the occurrence, circulation, distribution, and properties of the waters of the earth and its atmosphere.

hydrometer :
an instrument for determining the specific gravity of a liquid, commonly consisting of a graduated tube that's weighted to float upright in the liquid whose specific gravity is being measured.

hydrophone :
a device for detecting sounds transmitted through water, as for detecting or locating marine life or other objects moving underwater.

hydroplane :
a hydrofoil attachment to an airplane enabling it to glide on the surface of the water; a seaplane. Also, a high-powered, lightweight boat with a stepped bottom or hydrofoils, enabling it to plane across the surface of the water at high speeds. Also, a horizontal rudder used for submerging or elevating a submarine.

hydrostatic pressure :
fluid force exerted on the body's equilibrium, such as the amount of pressure from the weight of water above a submerged diver.

hydrostatic test :
the required annual examination of pressurization tanks that are filled with water instead of air.

hyperbaric chamber :
a steel vessel in which atmospheric pressure can be raised or lowered by air compressors, used to treat aeroembolism, and to provide a selective air mixture environment for certain medical procedures; also called a decompression chamber.

hypercapnia :
the presence of an excessive amount of carbon dioxide in the blood. A result of shallow skip breathing or excessive hyperventilation in free diving, as well as Deep Diving on compressed air. Hypercapnia will let nitrogen narcosis increase as well as making it more likely that oxygen toxicity will occur; heat loss can be increased, Heart rate and rhythm altered, and decompression illness will be more likely to occur.

hyperventilation :
prolonged rapid or deep breathing that's undertaken in a deliberate effort to extend the duration of a free dive, resulting in excessive oxygen levels in the blood, often with accompanying dizziness, chest pain, and tingling of extremities, then culminating in the presence of an excessive amount of carbon dioxide in the blood (hypercapnia).

hypolimnion :
the layer of water below the thermocline, being that underlying region of a thermally stratified lake or reservoir in which there is a rapid decrease in temperature with water depth.

hypothermia :
a subnormal body temperature; a drop in the body's core temperature as a result of exposure to cold. [nb: heat is transferred from the human body at a rate of twenty-five to seventy times more in water than in air]

hypoxemia :
the inadequate oxygenation of the blood.

hypoxia :
an abnormal bodily condition in which oxygen intake is insufficient or utilization is inadequate to sustain normal activity; often exhibited as unconsciousness.

abbreviation for the International Association of Handicapped Divers.

abbreviation for the International Association of Nitrox Divers.

abbreviation for the International Association of Nitrox and Technical Divers; alternatively as the International Association of Nitrox and Trimix Divers ... a group of recreational divers with technical diving qualifications.

ice anchor :
a large, hooklike device for setting in ice to anchor a vessel, or to provide a hold for a hawser in warping it along; also called "ice drag".

iceberg :
a large mass of ice, detached from a glacier, and floating out to sea.

iceblink :
a yellowish luminosity near the horizon or on the underside of a cloud that's caused by the reflection of light from sea ice; also called "blink", as derived from 'blink' meaning gleam, twinkle, glitter, or shine.

ice-crystal haze :
a type of very light ice fog composed only of ice crystals (no droxtals or water vapor) that's usually associated with ice crystal precipitation, and is observable to altitudes as great as 7000m. Viewed from the ground, ice-crystal haze may be dense enough to hinder observation of celestial bodies, sometimes even the sun. However, when viewed from above, the ground is usually visible and the horizon only blurred. For very sparse ice-crystal haze during daytime, sunlight reflecting from crystal faces produces sparkling in the air, which crystallization is commonly known as "diamond dust".

ice diving :
a type of penetration diving that typically has only a single point of entry/exit through the overhead ice layer, so requires advanced training, specialized gear and insulated clothing, a rescue partner and a recovery environment; ice diving is primarily undertaken for commercial, scientific, or military purposes. The ice diver frequently combines buoyancy control devices due to their importance, and is tethered to the surface by a recovery line that's also used to communicate with the standby support team ... shifting pack ice has the potential to pinch the tether and close-off access. Underwater time for decompression is complicated by extreme temperature, and thermal exposure suits are not a substitute for shelter ... descent and ascent may be augmented by use of a pod or bathyscaphe. Redundant systems should include an environmentally sealed regulator together with alternate air and duplicate buoyancy arrangements, and most ice divers wear a full face mask with a protective hood.

icefall :
a jumbled mass of ice in a glacier. Also, a mass of ice overhanging a precipice. Also, ice falling from a glacier, iceberg, or the like.

ice fog :
a type of fog partly composed of suspended ice crystals and droxtals, that occurs at very low temperatures, and usually in clear, calm weather in high latitudes; because the sun is usually visible, it may cause halo phenomena. Ice fog is almost always present at air temperatures of -13°F/-45°C in the vicinity of a source of water vapor, such as herds of animals, volcanoes, the open water of fast-flowing streams or of the sea, and especially products of combustion for heating or propulsion. Ice fog is also known as "ice-crystal fog", "frozen fog", "frost fog", "frost flakes", "air hoar", "rime fog", and "pogonip".

ice foot :
a belt of ice frozen to the shore, formed chiefly as a result of the rise and fall of the tides.

impoundment :
a body of water confined within an enclosure, as a reservoir.

inch of mercury :
a unit of atmospheric pressure, being the pressure equal to that exerted by a column of mercury one inch high under standard conditions of temperature and gravity (ie: 33.864 millibars); abbreviated "in Hg".

independent doubles :
an arrangement of double cylinders without a manifold, as used with side-mounts, which requires a complete regulator setup for each cylinder.

inert :
having little or no ability to act, react, or interact; having no inherent power of motion or resistance.

inert gas :
any chemically inert gaseous element, such as helium, neon, argon, krypton, xenon, and radon; found in group 8A or 0 of the periodic table, and also known as "noble gas".

inflator valve :
the valve on a buoyancy compensator where a low pressure hose from the second stage can be used for inflation; typically includes a mouthpiece for oral inflation.

inlet :
an indentation of a shoreline, usually long and narrow, such as a small bay or arm. Also, a narrow passage between islands. Also, a point of entry or place of admission; entrance.

Ino :
a sea goddess who rescued Odysseus from drowning by giving him a magic veil.

intercostal :
between the ribs; the muscles between the ribs which contract during inspiration to increase the volume of the chest cavity.

intermediate pressure :
a step-down pressure from the high pressure scuba cylinder to the ambient pressure at depth, making regulator function more consistent; common intermediate pressure (IP) is 120-180 psi (8-12 bar).

International Ice Patrol :
an annual U.S. Coast Guard patrol of the North Atlantic ocean during the ice season to ascertain the locations of icebergs so as to warn ships at sea: undertaken after a 1914 agreement among fourteen maritime countries.

International Orange :
a shade of bright orange, highly visible at a great distance and in murky weather, that's been used since 1955 to color rescue or emergency gear, safety devices and appliances, survey equipment and vehicles, including boats and aircraft, hangars and control towers; also known as "safety orange" or "blaze orange".

interstitial emphysema :
gas trapped in the chest after lung barotrauma.

intertidal :
pertaining to the littoral region that is above the low-water mark and below the high-water mark.

IP :
abbreviation for intermediate pressure.

iridescence :
a play of lustrous, changing colors.

ischemia :
a local deficiency of blood supply that's produced by obstacles to the arterial flow, by vasoconstriction, or by other inadequacies of a part or organ.

island :
a tract of land that's completely surrounded and detached; as derived from isolate. [nb: a seaman defines an island as a hazard to navigation that's inhabited by drunks, whores, thieves, farmers, and other lubbers who were stupid enough to abandon the ship!]

isle :
any island, especially when small.

islet :
a very small island.

abbreviation for the International Standardization Organization.

isotherm :
a curve representing changes in volume and pressure while at the same temperature.

isthmus :
a narrow strip of land, bordered on both sides by water, connecting two larger bodies of land; also called a neck or strait.

jackline :
a rope, webbing, or wire cable that's strung from padeyes or cleats along the port and starboard sides of a ship, from bow to stern, during foul weather and limited visibility, so that a safety harness ("jackline harness") can be connected, allowing passengers and crewmembers to move safely on the topside deck whenever there's a risk of falling or being swept overboard; a temporary safety rigging to secure lives aboard a vessel during hazardous conditions.

jack-up rig :
a buoyant hull fitted with several movable legs, each fitted with 'spud can' feet to help distribute the load so the rig doesn't sink too deeply into the seafloor, which serve to raise this mobile platform and its machinery as a unit above the surface of the sea, once properly positioned at the desired location.

Jacob's ladder :
a flexible ladder consisting of rope, cable, or chain side-rails and fixed wooden or aluminum rungs, as used on vessels and aircraft; also called a "pilot ladder" or "jack ladder", "caving ladder" or "scaling ladder", as derived from the Biblical dream of a ladder ascending from earth to heaven. Also, a webbing or rope ladder deployed for insertions and/or extractions of people employing transport vessels or aircraft instead of debarkation nets or rappel lines.

Jasper reel :
a reel that has the handle located on one side of the spool, instead of the top, so as to more easily payout (and retrieve) guideline when exploring new cave passages; as advocated by Woody Jasper, a Florida cave diver.

jetsam :
goods or supplies that are deliberately cast overboard from a vessel so as to lighten or stabilize it in an emergency, as derived from "jettison"; such cargo typically sink where castaway, but may be later washed ashore.

jetty :
a pier or structure of stones, piles, or the like, projecting into a body of water to protect a harbor, deflect the current, or other stabilization. Also, a wharf or landing pier. Also, the piles or wooden structure protecting a pier.

jewel block :
a block at the end of a yard or gaff that's used for supporting a signal or ensign halyard; also called "dasher block".

jibe :
to alter course so that a fore-and-aft sail, or its boom, shifts from one side to the other when running before the wind.

jolly boat :
a light boat carried at the stern of a sailing vessel.

Jonah :
a person or thing regarded as bringing misfortune or bad luck; a jinx, as derived from the minor prophet in the Bible who's thrown overboard from his ship for his impiety.

Jonline :
a length of line typically used to attach to a shot line or anchor line to provide horizontal spacing for decompressing divers at the same stop depth.

Joule's law :
the principle that the internal energy of a given mass of an ideal gas is solely a function of its temperature; a secondary law of thermodynamics [v: joule = SI unit of energy] named after James Prescott Joule, an English physicist.

jury mast :
a temporary mast that has been erected to replace one that was lost or destroyed.

jury-rig :
to repair or assemble something hastily, or from whatever is at hand, as for temporary use; to improvise an expedient or makeshift.

J-valve :
a spring-loaded mechanism which shuts off a diver's air supply when reduced to a certain tank pressure, as was formerly used to trigger the switch to the reserve air supply, and compel the diver's ascent; superseded by the submersible pressure gauge (SPG).

karst :
an irregular limestone terrane featuring sinkholes, fissures, caverns, and underground streams that's caused by erosion from carbon dioxide enriched water.

kayak / kaiak / kyak / kyack / qayaq :
a double-ended Eskimo canoe with a skin cover on a light framework that's made watertight by a flexible closure around the waist of the occupant, and is propelled with a double-bladed paddle; a commercially made small boat that has been created to resemble the original Eskimo design, but is manufactured in a variety of modern materials for sporting or touring applications.

kayak diving / canoe diving :
use of a small lightweight vessel for access to remote or obscure dive sites, especially rivers, as when drift diving; an alternative to boat or shoreline access.

kedge :
to advance a vessel or load along a waterway by pulling incrementally, as with a small anchor; as derived from to tie or fasten. Also, the small anchor used for such incremental hauling.

keel :
a central fore-and-aft structural member in the bottom of a ship's hull, extending from the stem to the sternpost; in Asia it's known as a "dragon's spine".

kelvin :
the base unit of temperature in the International System of Units (SI) which is defined to be 1/273.1 of the triple point of water. [nb: the degree intervals of the kelvin scale are the same as celsius, as the rankine are the same as fahrenheit]

kernmantle :
a synthetic-fiber rope constructed with a plaited sheath surrounding an inner core of either parallel or twisted core strands.

key :
a reef or low island; properly called 'cay'. Also, a pin, bolt, wedge, or other piece that's inserted into a hole or space so as to hold the parts of a mechanism together. Also, slang for a unit of measure (mass) equivalent to one kilogram (kg).

kilo :
short for kilogram, being the base SI unit of mass; the metric value of 1000 grams, with 1 kg equal to 2.21 lb. Also, short for a unit of force, equal to the force that produces an acceleration of 9.80665 meters per second per second when acting on a mass of one kilogram. Also, short for kilometer, being the base SI unit of length; the metric value of 1000 meters, with 1 km equal to 3280.8 ft or 0.621 mi.

king wave :
see sneaker wave, rogue wave.

kit :
collective reference to all of the diving equipment required to make an underwater dive. [v: kit 'n' caboodle]

knee-knocker :
slang for the protective rim or bulwark surrounding an opening in a bulkhead or deck, designed to exclude water; this coaming is also called a "shin-scraper".

knighthead :
either of a pair of upright members (apostle) flanking and securing the bowsprit of a ship at the bow, often used as mooring bitts. Also, a plate at the fore end of a forecastle through which a spike bowsprit passes on a topgallant sailing ship.

knot :
a constrictive interlacement used for fastening rope, line, cord, and the like. Also, a unit of speed equal to one nautical mile (or about 1.15 statute miles) per hour. Also, a unit of measure, being either one nautical mile, or a line marked 47'3" (13.79m) long.

Kraton :
the brand name (GLS trademark) of a synthetic rubber (thermoplastic polymer) that can be molded to form a handle that provides a non-slip grip while retaining flexibility. [v: gutta-percha, India rubber, para rubber]

K-valve :
a simple on/off valve; a standard yoke-style valve without a reserve lever.

ladderwell :
the staircase, usually skeletonized, whether fitted with rungs or steps, with or without handrails ("ladderrail"), running between decks on-board ships.

lagan :
goods that are deliberately thrown or sunk in the sea but are attached to a buoy so that they may be recovered, being a form of jetsam; as derived from a net laid in the sea.

lagoon :
any small body of shallow water that's connected to a larger body by an intermittent or restricted flow, or separated from the sea by a natural barrier of dunes or reefs.

lake :
a considerably sized body of either fresh or salt water that's surrounded by land.

Lake guns :
the name given to mysterious booming sounds that seemingly come from nearby phenomena situated offshore at Seneca Lake, New York.

lambert :
the centimeter-gram-second (cgs) unit of luminance or brightness, equivalent to 0.32 candles per square centimeter and equal to the brightness of a perfectly diffusing surface emitting or reflecting one lumen per square centimeter; abbreviated: L.

Lambert's law :
the law that the luminous intensity of a perfectly diffusing surface in any direction is proportional to the cosine of the angle between that direction and the normal to the surface, for which reason the surface will appear equally bright from all directions; also called "cosine law", named after the German mathematician Johann Heinrich Lambert. [v: Beer-Lambert law of optics; Willebrord van Roijen Snell law of refractive index]

landing :
a place where persons or goods are landed, as from ship to shore, shore to ship, or from ship to ship; also called landing platform. [cf: float, stage]

laryngospasm :
severe constriction of the larynx in response to the introduction of water or noxious stimuli; commonly called choking.

latitude :
an imaginary circle on the earth's surface formed by the intersection of a plane parallel to the plane of the equator, bearing east and west, and designated in degrees of latitude north or south of the equator along the arc of any meridian of longitude; also known as "parallel of latitude".

lave :
to flow along, against or past; as the tide washes the shore, or when a current washes the seafloor.

lay line :
term used by cave divers to designate the initial exploration line in a previously unexplored ("virgin" or 'booty') cave system.

lead :
an opening or direction that affords passage to a place, such as an open channel through a field of floating ice. Also, the direction of a rope, wire, or chain. Also, the distance between the center of lateral resistance and the center of effort of a sailing ship, usually expressed decimally as a fraction of the water-line length.

leading edge :
the edge of an airfoil or propeller blade that's facing in the direction of motion. [v: chord] Also, the forward edge of a mass of air or water.

leader :
any of various devices, smooth and open, for guiding a running rope; also called 'lead'.

league :
a unit of distance which has varied at different times and places, apparently originating as the Gaulish equivalent of 1.5 Roman miles, but lately measures about 3 miles (4.8km) in English-speaking countries. [nb: 12 inches = 1 foot, 3 feet = 1 yard, 6 feet / 2 yards = 1 fathom, 16.5 feet = 1 rod (aka: pole or perch), 66 feet / 4 rods = 1 chain (90 feet / 15 fathoms = 1 anchor chain), 10 chains / 660 feet (1/8 statute mile) = 1 furlong, 120 fathoms / 720 feet = 1 land cable, 101 fathoms / 606 feet (1/10 nautical mile) = 1 cable, 3 statute miles = 1 land league, 3 nautical miles = 1 sea league / shot]

abbreviation for light emitting diode, a rugged and robust electron tube that's replacing traditional incandescent bulbs in portable lights.

ledge :
a reef, ridge, or line of rocks in a body of water.

lee :
the part that's sheltered, or the side that's turned away from the wind; the point or quarter away from the direction of the prevailing wind.

leech :
either of the lateral edges of a square sail; or the after edge of a fore-and-aft sail.

leech line :
a line for hauling the middle of a leech of a square sail up to the yard.

leech rope :
a boltrope along a leech.

leeward :
in the direction away from the prevailing wind; toward the point or quarter away from which the wind blows; moving toward a sheltered or protected place that's out of the wind.

leeway :
the drift of a vessel from its course or heading due to crosswinds or currents [cf: leeward, windward]. Also, a margin of space, time, or materials, being an extra or surplus; a degree or element of freedom, of latitude.

leisure diver :
see holiday diver, recreational diver.

Leucothea / Leukothea :
a sea goddess in classical mythology who gave Odysseus a veil as a float after a storm had destroyed his raft; also known as "the white goddess", and later deified as Ino.

Lexan :
a trademarked brand of hard, tough, transparent polycarbonate resin that's used to make shatterproof windows, protective goggles, and other practically unbreakable objects. [nb: a preliminary treatment of polycarbonate (eg: Lexan) windows with acetone / dimethylketone will sufficiently compromise its inherent structure so that it will shatter under impact]

lifeboat :
a double-ended accessory craft, also called a dinghy or tender, required to be available on any aircraft or vessel operating on or over water, usually stocked with a limited supply of medical equipment and survival provisions, so as to enable passengers and crew to be rescued from sinking. Also, a similarly constructed and mounted watercraft that's provisioned for shore-based rescues at sea.

life car :
a watertight container used in marine rescue operations since the mid-19th century that has been suspended from a hawser so it can be hauled back and forth between a stranded or wrecked vessel and the shore; also called safety car or ark.

life jacket :
a sleeveless jacket of buoyant or inflatable construction that's used for supporting the wearer in deep water so as to prevent drowning; also called "life vest" or "air jacket" (British).

lifeline :
a line or rope available for saving life, as one attached to a lifeboat, or a heave line cast from a vessel. Also, any of various lines running above the decks, between spars or other structures of a ship or boat, giving sailors something to guide or grab when in danger of falling overboard or washing away. Also, the line by which an underwater diver is lowered and raised. Also, any of several anchored lines used by swimmers for support.

life raft :
a manufactured raft, often inflatable, that's stowed for use in emergencies, as when a ship must be abandoned or when a plane is downed at sea.

lifesaving leap :
see giant stride entry.

lift bag :
a type of underwater balloon or specialized buoyancy compensator that can be attached to a submerged object, inflated with air, and brought to the surface without great exertion; available in either small or large capacity, and may be joined in series for heavier loads.

lift capacity :
the amount of buoyancy provided by a buoyancy compensator, which varies by size and by environment (eg: water temperature, water salinity, etc).

lighter :
a large, open, flat-bottomed vessel used to transport cargo from ship to wharf, often towed or pushed; a sailless junk or barge used to ferry passengers, especially when reserved for pageants.

limber hole :
any of a series of holes pierced through a frame or floor to allow the passage of accumulated moisture. [cf: weep hole]

limnology :
the scientific study of bodies of fresh water, such as lakes and ponds, with reference to their biological, geographical, physical, and other features.

line :
a rope, cable, or other cordage used on a vessel or at sea. Also, any actual or representative connection, as in communications. Also, a course of direction, as a route or heading. Also, indication of a boundary or limit, as a demarcated safety zone. Also, an outline or contour.

line squall :
a storm that advances along a front forming a more or less definite line.

liquescent :
becoming liquid; tending toward a liquid state; melting.

list :
to lean to one side, or to cause to incline toward one side, as a ship or other vessel; sway or careen.

littoral :
pertaining to the shore of a lake, sea, or ocean. Also, pertaining to the biogeographic region between the sublittoral zone and the high-water line on ocean shores, and sometimes including the supralittoral zone above the high-water line. Also, pertaining to the region of freshwater lake beds from the sublittoral zone up to and including damp areas on shore.

littoral drift :
see beach drift.

load-line mark :
any of various lines marked on the sides of a cargo vessel to indicate the depth to which a vessel may be immersed under certain conditions; also represented as load-line, load line, or boottop.

loch :
a lake. Also, a partially protected or landlocked bay; a narrow arm of the sea.

lock :
an enclosed chamber in a canal, dam, or other impoundment with gates at each end, that's used for raising or lowering vessels from one level to another by admitting or releasing water. Also, short for an air lock or decompression chamber.

locked-in :
a precarious position for a vessel at sea during a violent storm wherein that vessel is unable to escape the powerful waves blocking it on either side.

log / logbook :
a record of a diver's history that catalogues, at a minimum, the date, location, depth, duration, type, gear, and sequential total of dives; many divers include transport, party, weather, and any observations or incidents.

log line :
the trailing line by which a log or patent log is streamed from a vessel in naval navigation.

longitude :
(forthcoming); aka: meridian of longitude

loop :
a sand bar that encloses (or nearly encloses) a body of water.

lost river :
common referent for a flowing waterway that disappears underground at one or more points during its course of travel.

lotic :
pertaining to or living in flowing water; as derived from "wash".

low pressure cylinder :
steel air cylinders that're used at fill pressures of 2,400 psi (160 bar).

low pressure inflator :
an extra hose from the second stage regulator that provides air to inflate the buoyancy compensator through the inflator valve; typically includes a mouthpiece for oral inflation.

low volume mask :
a mask which has a smaller area between the glass and the diver's face, usually with separate lenses for each eye, such that less air is required to purge when it becomes flooded.

lox :
abbreviation for liquid oxygen.

LP :
abbreviation for low pressure.

LP hose :
the low pressure hose that connects the first stage of the regulator to the second stage or inflator.

abbreviation for Liters Per Minute; a measurement of the flow rate of a liquid or gas.

lubberly :
to be awkward or inexperienced around watercraft, such as a "landlubber"; also represented as "slubberly" for careless and "Dutch talent" for unskilled; to be "ham-handed" rather than "dab-handed".

lubber's hole :
an open space near the top on a mast through which a sailor may pass to reach a perch, instead of climbing out on the futtock shrouds. [v: futtock shroud: any of several metal rods secured at their lower ends to a futtock band and at their upper ends to a futtock plate, connecting the lower mast to the topmast rigging]

luff :
to set the helm so as to bring the head of a ship closer or directly into the wind, with sails shaking. Also, to raise or lower the outer end of the boom of a crane or derrick, moving its load horizontally.

abbreviation for Low Water Level.

main deck :
the uppermost weatherproof deck on a vessel, running the full length of the ship.

mainstay :
anything that serves as chief part or primary support; including an essential person, such as the "anchorman" or "right-hand man". Specific naval use as the stay that secures the mainmast forward.

main walkway :
a floating structure in a marina to which finger floats are attached so as to define individual berths, and to provide pedestrian access between the berths and a marginal walkway or the shore.

makefast :
any structure to which a ship is tied up, as a bollard or buoy. Also, to securely tie onto such a structure.

make way :
an informal directive to get out of someone's way; a warning to get out of the way of something that's not responsive, or is out of control.

making way :
when a vessel is proceeding by its own power, whether manual or mechanical propulsion; also represented as "making headway".

manifold :
a connection that enables a single regulator to access the breathing gas in both pressure tanks; a double cylinder system that's connected by a heavy duty crosspiece with a valve in the center.

manometer :
an instrument for measuring the pressure of a fluid, consisting of a liquid filled tube, the level of which indicates the fluid pressure in decibars (dbar) or bars on a calibrated scale. Pressure is commonly measured by its ability to displace a column of liquid in a tube, which is often expressed in a measure of that liquid (eg: inches of mercury). [nb: a rule of thumb used by divers states that the pressure exerted by ten metres depth of water is approximately equal to one atmosphere]

marginal walkway :
a floating structure in a marina that provides pedestrian access between two or more main walkways and the shore, and may serve as a platform for lighting, fuel stations, sewage pumpout facilities, lift stations, and utility lines.

marina :
a boat basin offering dockage and services for recreational small watercraft, including wet and dry storage.

marker :
a high visibility indicator, typically luminous or reflective or brightly colored, that's used to designate the correct or safest path through an entanglement or maze; also called "route marker" or "trip beacon", "guidepost" or "signpost", these signals may be temporary or semi-permanent, and employed whenever a safety line is inappropriate. [v: lodestar, polestar]

marl :
a friable earthy deposit consisting of clay and calcium carbonate, as floating suspended in murky or turbid waters, and coating anything drawn from those waters; an archaic term for earth or soil. Also, to wind a rope or cable with marline, every turn being secured by a hitch; as derived from "ensnare" (marlyn).

marline / marlin :
light cordage of two-fiber strands, laid up left-handed.

marlinespike / marlinspike :
a smooth, tapered, steel tool used to open the strands of a wire cable for splicing.

Martini's law :
an approximation for a relative comparative scale of competence and coordination, wherein each 50 feet of depth breathing air underwater is the equivalent of one martini consumed on an empty stomach; a condition most noticeable at depths of 100 feet of sea water (fsw) and below.

mask :
a protective cover consisting of a skirted transparent window (ie: plexiglas) constructed to provide air space between the eyes and the exterior water, permitting both eyes to see in the same plane, and usually made of neoprene, silicone, or another synthetic rubber. A regular diving mask covers only the eyes and nose, while a full face mask encloses the entire face. The mask is also called a "swim mask", "face mask", or "diving mask", and is available in a low volume style.

mask squeeze :
an uncomfortable or painful condition created when the air inside the dive mask is compressed by the external pressure, causing a suction on the face and eyes that swells delicate tissues, which can cause permanent eye damage if not equalized; this imbalance can be alleviated by exhaling through the nose.

mast :
a structure rising above the hull of a ship for holding spars, rigging, and associated equipment. Also, any upright pole, post, or support, as for a radio aerial. Also, the support for a crane or derrick, boom or davit, yardarm or block 'n' tackle.

maximum operating depth :
the depth at which the partial pressure of oxygen (ppO2 / ppO2) of a gas mix exceeds a safe limit. Also, the lowest safe depth at which a submarine or other submersible is not to exceed during normal operations; this "never exceed depth" is a determination made by naval authority in consideration of design and manufacturing limits, and has been specified as half (Europe) or two-thirds (USN) of the test depth.

abbreviation for Massive Catastrophic Decompression; also known as "explosive decompression", wherein air pressure erupts through the human body as a result of improper nitrogen off-gassing after deep-sea diving.

meander line :
a zigzag traverse made to define the approximate margin of a natural body of water, as for mapping or surveying.

mediastinum :
the area in the chest that lies between the lungs, is bounded by the sternum, the spinal column, and the diaphragm, and contains the heart, esophagus, trachea, and other thoracic structures; term derives from "a low ranking slave".

meridian of longitude :

messenger :
a smaller line used to haul a heavier line or cable across an intervening space; also known as "messenger line", "heaving line", or "throw line".

metabolism :
the sum of the physical and chemical processes in an organism by which its substance is produced, maintained and destroyed, and by which energy is made available. [cf: anabolism, catabolism]

meters of sea water :
a unit of pressure, which varies slightly with temperature and salinity, but a practical convention accepts that each meter of sea water imposes a pressure of 0.1 bar (DBAR), or that each meter is equivalent to 0.1 atmosphere (0.1013 bar); abbreviated msw.

abbreviation for Mean High Water.

mil-spec polypropylene :
a tough, heat-resistant, semi-rigid thermoplastic that offers a combination of outstanding physical, chemical, and mechanical properties, with superior working temperature and tensile strength, is light in weight, resistant to staining, and has a low moisture absorption rate.

minisub :
a small submarine, holding only one or a few persons, as used in naval special operations, underwater explorations, or when conducting underwater experiments; a contraction of miniature submarine, and also called "midget sub".

mistpoeffers :
the name given to mysterious booming sounds that seemingly come from nearby occurrences at sea, being situated off the coast of Holland and Belgium.

mixed gas :
any breathing medium that is blended with oxygen and other gases, having either a single inert gas (eg: heliox, nitrox) or multiple inert gases (ie: trimix).

abbreviation for Mean Low Water.

abbreviation for Maximum Operating Depth, being the deepest that a diver can safely go using a particular gas mixture [eg: EAN32 at 132 fsw (40m)].

mole :
a breakwater, groyne / groin, or jetty used to form or protect an anchorage or harbor, to reinforce or protect a pier, wharf, or quay.

monkey block :
a small single block that swivels. Also, the blocks fastened to a yard or yardarm through which buntlines are rove.

monkey bridge :
a small open deck, situated above the main cabin or pilothouse of a vessel, having duplicate bridge controls; also called "flying bridge" or "bridge deck". Also, a raised fore-and-aft catwalk permitting safe passage when the weather deck is washed by heavy seas; also called "flying gangway".

monkey fist / monkey's fist :
a casting knot (often a figure-8 on a bight) added to the trailing-end of a rope or line to lend weight and direction for throwing; a ball-like knot used as an ornament or as a throwing weight at the end of a line; sometimes called "monkey paw" or "monkey's paw" by a fancied resemblance. [nb: may be made by tying a bag of lead shot to the end of a rope]

monkey island :
slang for a flying bridge (qv) on top of a pilothouse or chart house.

monkey jacket :
a short, close-fitting serge jacket or coat that was formerly worn by sailors; also called "jackanapes jacket", being so-called from its resemblance to a jacket worn by an organ-grinder's monkey.

monkey rail :
in modern vessels, a small railed perch above the ship's stern enclosing standing room that permits an officer to supervise the handling of mooring-lines when docking, or to observe loading and unloading; in older vessels, a topgallant rail above the quarterdeck or poop bulwarks (quarter boards).

monkey tail :
slang for any of various short ropes or light lines.

moonpool :
the pond contained within the hull of a surface ship or in the chamber of a moored platform that provides subsurface access to the surrounding waters, especially for launching and recovering submarine vessels through an underwater opening (shell door); such a reservoir is generally capable of being sealed and isolated from the rest of the environment as a safety precaution.

moor :
to secure a ship, boat, or other vessel in a particular place by lines, cables, or anchors.

mooring pile :
a pile situated at the entrance to and in the center of a double berth, to which both vessels may be secured.

mossback :
an old fashioned sailor, as from a canny fish or wise turtle, especially a traditionalist, conservative, or reactionary; also called a sea dog, old salt, or shellback.

motorboat :
a vessel propelled by a small but powerful internal-combustion engine that's mounted inboard or outboard.

mouthpiece :
the demand valve receptacle, held in the diver's mouth, at the terminus of the regulator assembly of a scuba apparatus; a similar device (without pressure stage) terminates a snorkel.

abbreviation for Metres of Sea Water, a pressure measurement.

mudlump :
an Americanism for a small temporary island at the mouth of a river; a short-lived islet of clay or silt formed by deposits within a river delta.

multiday :
a dive series with a surface interval of more than 24 hours between consecutive dives; dives that require a substantial delay so extending the time on station; juxtaposed to single-day.

multilevel dive / multilevel diving :
a dive profile that extends over more than one depth, expending time at each, before finally returning to the surface; juxtaposed to square dive / square diving.

mushroom valve :
a small flexible valve, such as is used as an exhaust valve in second stage regulators and as a check valve in the mouthpiece of re-breathers.

abbreviation of the National Association for Cave Diving; also represented as NA4CD.

abbreviation for National Association of Scuba Diving Schools, formed in 1962, which merged with Scuba Schools International (SSI) in 1999.

narrows :
a narrow part of a strait, river, channel, ocean current, or other body of constricted water.

abbreviation for National Association of Underwater Instructors, which was formed as a nonprofit professional organization in 1959, spawning the Professional Association of Diving Instructors (PADI) in 1966.

nautical mile :
officially known as the "International Nautical Mile", being a unit of distance at sea or in the air equal to 1.852 kilometers. Also, a unit of distance, formerly used in the U.S. for navigation, equal to 6080.20 feet (1853.25 m), or the length of a minute of latitude at the latitude in question (decreasing toward the poles); abbreviated NM. [nb: a "geographic mile" is the length of a minute of longitude on the equator]

abbreviation for No-Decompression Limit.

neck :
a strait or channel; narrows. Also, a narrow strip of land, as an isthmus or a cape.

neo-Haldanean / neo-Haldanian :
decompression models based on later modifications (eg: critical difference hypothesis) of the principles described by John Scott Haldane.

nephelometer :
an instrument for studying the density of suspended particles in a liquid by measuring the degree to which the suspended particles scatter light; as derived from 'cloud' + 'measure'. Also, an apparatus containing a series of barium chloride standards used to determine the number of bacteria in a suspension.

Neptune :
the god of water in the Roman religion; being an indigenous god of fertility who was later identified with Poseidon, the Greek god of the sea; a festival, the Neptunalia, was annually (July 23) celebrated in his honor. Also, used allegorically to represent the sea or ocean.

neritic :
pertaining to the region of water lying directly above the sublittoral zone of the sea bottom; also called neritic zone.

newton :
the base unit of force in the International System of Units (SI) which is equal to the force that produces an acceleration of one meter per second per second on a mass of one kilogram.

niggerhead :
slang for an isolated coral outcropping, or any knob-like solitary protrusion, such as pillow lava, often semisubmerged, that's a hazard to navigation. Also, naval slang for a small winch or capstan. Also, old reference in the British Navy for a mooring post made from a cannon, buried muzzle upright, that's capped with a slightly oversized ball. Also, a large decorative knot, used to finish a special line or lanyard (such as one suspended from the clapper of a ship's bell); sometimes called "Turk's Head".

night diving :
because some sealife is nocturnal, or behaves differently at night, many sport divers (who rarely venture below the 33 foot depth of one standard atmosphere) encounter a new world when diving underwater at night. [nb: in open water, sunlight does not penetrate below a depth of 90 feet or two atmospheres of pressure]

NiMH :
abbreviation for Nickel Metal Hydride, being a high capacity rechargeable battery that's more tolerant of abuse and resistant to overcharging than nickel-cadmium batteries.

nip :
an abrupt turn or twist in a rope. Also, a part of a rope or chain bound by a seizing or nipper. Also, to seize a taut rope to another rope.

nipper :
a short rope for seizing an anchor cable to a messenger from a capstan.

nitrogen :
a colorless, odorless, inert gaseous element that constitutes about 78% of the volume of the atmosphere and is present in combined form in organic tissues; it's used by divers in varying concentrations as part of the breathing gas mixture, with specific side-effects (eg: nitrogen narcosis, decompression sickness).

nitrogen narcosis :
a stupor or euphoria, also called "rapture of the deep", that's induced in deep-sea divers when nitrogen from air enters the blood at higher than atmospheric pressure.

nitrox :
a gas mixture of nitrogen-oxygen with an oxygen content other than 21%, with "oxygen-enriched air" and "enriched-air nitrox" rated greater than 21%, that's used to extend the no-decompression limit; the most common nitrox mixtures are NOAA Nitrox I at 32% oxygen and NOAA Nitrox II at 36% oxygen.

nm :
the abbreviation for nautical mile, also known as "International Nautical Mile". [cf: geographic mile]

abbreviation for the National Oceanic and Atmospheric Administration, in the U.S. Department of Commerce; which is responsible for describing the earth's environment and predicting changes in conserved or managed resources.

noble gas :
any chemically inert gaseous element, such as helium, neon, argon, krypton, xenon, and radon; found in group 8A or 0 of the periodic table, and also known as "inert gas".

nocturnal :
night, nighttime, or nightly; as juxtaposed to diurnal.

no-decompression :
a dive that does not require any staged stops during the return ascent to the surface; a dive profile scheduled by the use of tables or computer.

no-decompression limit :
a mathematical representation, plotted in minutes, of the theoretical amount of nitrogen that body tissues can absorb without substantial risk of decompression sickness.

no-mount / dismount :
the removal of back-mounted air tanks, together with any other bulky gear, which is pushed through an opening ahead of the diver when required to squeeze through constricted passages or wedge into confined spaces while exploring under water; a method of stripping down to essentials when otherwise too bulky to pass through a narrow aperture.

abbreviation for the National Speleological Society – Cave Diving Section.

oar :
a long shaft with a broad blade at one end that's used as a lever for rowing, or otherwise propelling, or for steering a boat. Also, to traverse or to make one's way by (or as if by) rowing.

oarlock :
any of various devices providing a fixed pivot for an oar in rowing, especially a crutch-like or ring-like metal contraption that can swivel while projecting above the boat's gunwale; also called rowlock.

ocean :
the vast body of salt water that covers almost three-fourths of the earth's surface, and commonly subdivided into geographic regions named the Atlantic, Pacific, Indian, Arctic, and Antarctic.

oceanic :
anything living in, generated by, or pertaining to the ocean, especially the vast region of water lying above the bathyal, abyssal, and hadal zones of the sea bottom. Also, pertaining to the islands of Oceania, its peoples, their languages and cultures.

oceanicity / oceanity :
the degree to which the climate of a (coastal or inland) place is influenced by the sea.

oceanography :
the branch of physical geography dealing with the ocean.

oceanology :
the science concerned with the practical application of oceanography.

octo :
short for octopus, an alternate regulator.

octopus :
slang for a backup or secondary regulator, usually attached to the same first stage as the primary regulator, and especially used in an out-of-air situation when aiding a buddy diver.

abbreviation for Oxygen Enriched Air, which designation is often synonymous with nitrox.

off-gas :
the elimination of inert gases (such as nitrogen) from the diver's body so as to avoid decompression sickness.

OK / okay :
a hand signal indicating safe and sound, correct or satisfactory, approval or agreement, being a gesture that forms an open circle with the thumb and forefinger, with the other three fingers spread and extended; also known as A-OK, this signal is also represented by making a circular motion with the dive light. This acknowledgement of status should not be confused with a "thumbs-up" sign, which means ascend.

old salt :
slang for an experienced sailor or master mariner; also called a sea dog, shellback, mossback.

on-gassing :
the absorption of nitrogen into various tissues that takes place as the partial pressure of nitrogen increases with depth.

on the beach :
someone who is not engaged in seafaring or not involved in marine activities; being unemployed or without a ship; being withdrawn or idle; being inactive or retired.

abbreviation for Out Of Air; the emergency situation when a diver has no breathing gas; also called "out-of-gas".

open-circuit SCUBA :
a scuba system that either recycles part of the exhaled air back into the breathing loop through a re-breathing scrubber, supplementing as necessary and exhausting the remainder, or discharges all of the exhaled air outside of the breathing loop. In contrast with 'closed-circuit scuba', this arrangement is commonly used in recreational diving, where noise and bubbles are not important considerations.

open sea :
the main body of a sea or ocean, especially that part which is outside territorial waters, and is either not enclosed or is only partially enclosed by land.

open water :
a designation, by various certifying authorities, of the primary level of scuba training; abbreviated OW. Also, a diving environment without obstacles or obstructions between the diver and the surface.

open water diving :
basic recreational diving that's performed in an unobstructed environment, one other than a swimming pool, such as an ocean or lake, river or quarry.

O-ring :
a small replaceable gasket, made of rubber or some other pliable synthetic (eg: neoprene, butyl, nitrile, Thiokol, Viton, EPDM), classified by size and hardness, which is used to close or seal watertight fittings. [cf: washer]

orlop :
the lowest deck above the space at the bottom of the hull of a ship; also called orlop deck.

outrigger :
the framework that extends outward from the side of a small boat to support a float that increases stability. Also, a spar rigged outward from a ship's rail or the like, as for extending a sail. Also, a projecting beam, as for supporting a hoisting tackle. Also, a bracket extending outward from the side of a shell or skiff to support an oarlock; or the boat itself so modified.

overboard :
over the side of a ship or boat, especially into the water. Also, to metaphorically go to extremes, as in behavior, speech, or the like.

overhead :
a ceiling-like covering of the exposed support members for the above compartment in a vessel. Also, an obstruction to a direct vertical ascent to the open water at the surface, as when cave diving or ice diving.

overhead dive :
underwater diving in wrecks or caves, or elsewhere without unobstructed open water to the surface.

overlay :
a transparent sheet that's placed over a map or chart for noting corrections, instructions, additional information, and the like.

OW :
abbreviation for Open Water; basic qualification for 'open water' certification can be earned after four hours of classroom (or computer) instruction, and the completion of four escorted scuba dives to a depth of 60 feet (18m).

oxygen :
a colorless, odorless, inert gaseous element that constitutes about 21% of the volume of the atmosphere and is present in combined form in organic tissues; it's used by divers in varying concentrations as part of the breathing gas mixture, with specific side-effects (eg: hypoxia, oxygen toxicity).

oxygen clean :
removing contaminants from an object so that nothing will adversely react with high pressures of oxygen; the removal of hydrocarbons (eg: oils and silicones) from an oxygen environment.

oxygen compatible :
materials that are suitable for exposure to oxygen, especially those that have been cleaned to remove any contaminants that could react with high oxygen pressures.

oxygen debt :
a deficiency of oxygen in the body resulting from strenuous physical activity.

oxygen re-breather :
the oldest type of re-breather, as once commonly used by navies, supplying only pure oxygen, which is toxic when inhaled under pressure, thus limiting its use to a depth of 20-30 feet (under 1 ATM). In some re-breathers, the oxygen cylinder has two first stages in parallel, one is constant flow and the other is a plain on-off valve called a "bypass"; both feed into the same exit pipe, which feeds the breathing bag. Some simple oxygen re-breathers had no constant-flow valve, but only the bypass, and the diver had to operate the valve at intervals to refill the breathing bag as the oxygen was used. Oxygen re-breathers are sometimes used when decompressing from a deep open-circuit dive, because breathing pure oxygen makes the nitrogen diffuse out of the blood more quickly.

oxygen partial pressure :
the concentration of oxygen in an air mixture, especially when combined in a dilute re-breathing or closed-circuit loop.

oxygen toxicity :
an abnormal bodily condition in which an increased concentrations of oxygen intake has over-exposed body tissues, which can result in convulsions or unconsciousness, leading to death by drowning; being a characteristic risk of breathing mixed gases under pressure.

pack ice :
a large area of floating marine ice whose pieces are driven together by wind and current; also called ice pack.

packet :
a small vessel that carries mail, goods, and passengers on a regular and fixed route; the first ships to keep a schedule, regardless of payload. Also, a small package or parcel.

paddle :
a short, flat-bladed oar that's usually held by both hands while being moved more or less through a vertical arc, as used for propelling and steering a canoe or other small boat. Also, any of the blades by which a water wheel is turned. Also, any of various similar implements used for turning, mixing, stirring, swirling, or beating any given medium. Also, an animal's use of its blade-like limbs or appendages (eg: flipper, fin, etc) to move through water or across the land.

paddleboard :
a variant type of surfboard with one end rounded and the other tapered to a point, which is used chiefly in competition, in touring, and in lifesaving. [cf: paddleboat, pedalboat]

abbreviation for Professional Association of Diving Instructors; formed in 1966 from the National Association of Underwater Instructors (NAUI), it's become the world's largest diver training and recreational diving membership organization.

paint pot :
in geological parlance, a spring or pit filled with boiling mud of varied colors; also known as "mud pot".

pan :
a drifting piece of flat thin ice, as formed on a bay or shore; term derived from face. Also, a natural depression in the ground, as one containing water, mud, or mineral salts. Also, an artificial depression in the ground, as made for evaporating sea water so as to obtain salt.

parachute flotation bag / parachute float bag :
an open-ended parabolic float, often rigged in pairs, that can be attached to a sunken object and lifted to the surface by inflation; because it's not completely enclosed (eg: caisson, camel, pontoon), maintaining proper balance or equilibrium is crucial, but this control factor is offset by the convenience in a less-bulky setup and more streamlined dismantling.

parallel of latitude :
the proper or formal name for 'latitude', being an imaginary line on the earth's surface connecting all points bearing east and west that are equidistant from the equator, which on most maps are shown in multiples of 5 degrees. Because of their special position, four fractional parallels are also shown: Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and Antarctic Circle. Parallels of latitude and meridians of longitude together form a grid by which any point on the earth's surface can be specified.

partial pressure :
the pressure exerted by any component gas in a mixture of gases, such as oxygen in air; the pressure that a gas in a mixture of gases, or dissolved in a liquid, would exert if it occupied the same volume as the mixture at the same temperature.

party :
a specific individual, especially one affiliated with others. Also, a group gathered for some special purpose or temporary task, such as a search party. Also, a social gathering for recreation or entertainment, usually involving conversation and refreshments; as derived from share.

pascal :
the base unit of pressure in the International System of Units (SI) which is equal to one newton per square meter; abbreviated Pa.

Pascal's law :
the law that an external pressure applied to a fluid in a closed vessel is uniformly transmitted throughout the fluid; named after the French philosopher and mathematician Blaise Pascal.

passageway :
an interior hallway that permits horizontal travel within a ship, as an aisle, corridor, or alley used as a pathway or walkway.

patent log :
any of various devices used for determining the speed of a ship by means of a vaned rotor streamed at the end of a trailing log line upon which it exerts torsion that's transmitted to a registering mechanism on-board; also called "screw log".

formed in 1965 as Professional Diving Instructors College, later changing its name to Professional Diving Instructors Corporation in 1984, which provides training in a retail environment.

pea jacket :
a blue, double-breasted, coarse woolen jacket worn by seamen or sailors; also called peacoat.

pelagic :
pertaining to the open seas or oceans; also called pelagic zone. Also, living at or near the surface of the ocean, as certain organisms growing far from land.

penetration line :
see distance line, cave line, guideline or safety line.

pennant :
a long tapering flag or burgee, as used for signaling or identification.

permanent thermocline :
a temperature gradient in a body of water that's not affected by the seasonal and diurnal changes in surface forcing; it is therefore located below the yearly maximum depth of the mixed layer and the influence of the atmosphere.

Personal Floatation Device; a life preserver in the form of a buoyant or inflatable vest.

phosphorescence :
the property or appearance of being luminous at temperatures below incandescence, as from slow oxidation or after exposure to light or other radiation. Also, any luminous radiation emitted from a substance after the removal of the exciting agent, as a phosphorescent wake.

pier :
a structure supported by flotation [floating pier] or built on posts extending from land [fixed pier] out over water that's used for access to or from the water (as a landing place for ships), and for other activities. Also, a square pillar used for support, as of bridge spans.

pierhead :
the outermost end of a pier or wharf. Also, informal regional reference to a breakwater.

pile :
a long slender structural member, typically composed of wood, concrete, steel, or plastic, that's driven into the seafloor of a basin or inlet to secure and guide docks.

pilothouse :
an enclosed structure on the deck of a ship from which it can be navigated; also known as wheelhouse.

pitch :
the up or down nosing of a ship about its transverse axis. Also, longetudinal oscillation or linear plunge, as a ship's alternating bow and stern rocking. Also, the distance that a given propeller would advance in one revolution.

pitch-pole :
a vessel capsizing lengthwise, due to waves cresting higher than the keel length.

plain sailing :
sailing on waters that are free of hazards or hindrances; being an easy course or unobstructed way.

plane sailing :
sailing a course that was plotted by a navigational method that didn't refer to the curvature of the earth. [v: spherical sailing]

plank :
a timber, thicker than a board, used on the deck or strake of boats and ships; also used as a brow or gangway (ie: gangplank).

plank owner :
a sailor who's been aboard since the vessel was commissioned into service; also called "plank holder". Also extended to persons who formed an initial party or the original group on an extended venture, project or voyage.

plankton :
the aggregate of passively drifting, or somewhat motile, organisms occurring in a body of water, primarily comprising microscopic algae and protozoa. [v: phytoplankton, zooplankton]

pleura :
one of a pair of serous membranes, each of which covers the outside of a lung, and folds back to line the corresponding inside of the chest wall and diaphragm.

Plexiglas :
the trademarked brand name of a lightweight, transparent plastic material (methyl methacrylate) that can be molded or cut to form tempered shields, prescription lenses, and many other objects.

plimsoll mark :
a contrasting line or band painted on the exterior hull of a merchant ship indicating its load level or depth level from the weight of its cargo; also known as Plimsoll line, load-line mark, load-line, boottop, or waterline.

plot :
to determine by means of measurements or coordinates, and to mark on a map or chart, a graphic plan or transparent overlay, the resultant course of a vessel or craft. Also, the place, located on or near the bridge, that's used for performing such calculations; also called "nav plot".

plume :
a moving fluid body that's rising or expanding, vertically or longitudinally, as of smoke or water; a flow or current that has been variously generated, as by subsurface heat or subterranean quakes. [v: megaplume]

plunge :
to rush or dash with headlong haste; to throw oneself impetuously or abruptly into some situation, circumstance, condition, matter, or the like; to bring suddenly or forcibly into some decision or conclusion. Also, to forcibly thrust something or to suddenly cast someone into a penetrable substance; to be immersed into a roiling mix, or to be submerged into a liquid. Also, a leap or dive, as into water; to cast oneself, or fall as if cast, into water, a hole, a shaft, or the like. Also, to descend abruptly or precipitously, as a cliff, ledge, road, or the like. Also, to pitch forward abruptly or violently, as a ship heaving along its longitudinal axis.

plunge basin :
a cavity formed by the action of falling water at the base of a waterfall or cataract.

plunge pool :
the churning water in a plunge basin, often generating a turbulent vortex; a light water pool, often of large size and situated either on the surface or underground, which occurs at the bottom of a waterfall or at the end of river rapids. [cf: water pocket, swirlhole]

pneumothorax :
the presence of air or gas in the pleural cavity as a result of compression or penetration, disease or inducement; a collapsed lung.

Poiseuille's law :
the law that the velocity of a liquid flowing through a capillary is directly proportional to the pressure of the liquid and the fourth power of the radius of the capillary, and is inversely proportional to the viscosity of the liquid and the length of the capillary; named after Jean Leonard Marie Poiseuille, a French physiologist. [v: Poiseuille's viscosity coefficient, Poiseuille's space]

pollywog :
an inexperienced or novice sailor, especially someone on his first float or cruise; also called chum, nugget, or fresh catch.

polynya :
an irregularly shaped area of persistently (unfrozen) open water that is sustained by warming winds or currents of ocean heat, which often occur near coasts, fast ice, or ice shelves.

polyurethane :
a thermoplastic polymer used to form insulation, sheeting, fabrics, and resin, having very good chemical and abrasion resistance, excellent strength, and resistance to the growth of microorganisms; 15-mil polyether aromatic polyurethane maintains its flexibility at low temperatures and can be seam welded (eliminating fittings), which reduces failure points.

abbreviation for polyoxymethylene (aka: acetal resin, poly glycol, polyacetal, and polyformaldehyde), an engineering thermoplastic used to synthesize precision parts requiring high abrasion resistance, low friction coefficient, high heat resistance, high stiffness, excellent dimensional stability, good electrical and dielectric properties, and low water absorption; under slightly different formulations, this heat and pressure formed (eg: injection-molding or extrusion) semi-crystalline polymer has been marketed as Delrin, Celcon, Hostaform, Duracon, Kepital, Iupital, and Ultraform when making gears and fasteners, hinges and insulators, lock mechanisms and knife handles. [nb: POM is not as strong as ABS or aluminum]

pond :
a body of water, smaller than a lake, which is sometimes artificially formed, as by damming a stream. Also, to collect into a pool, puddle, pan, or other pound; as derived from "impoundment". [v: dub]

pony bottle :
common term for a secondary gas cylinder carried by divers as a redundant air source; supplied with their own first and second stages, these tanks can be used as an alternate or emergency air source.

pool :
a small body of standing water; pond. Also, a still, deep place in a stream. Also, any small collection of liquid on a surface; puddle. Also, a subterranean accumulation; reservoir.

poop :
a wave breaking or taking seas over the stern of a vessel. Also, a superstructure or poop deck at the stern of a vessel.

poop deck :
a weather deck on the superstructure at the stern of a vessel, which may have bulwarks.

porpoise :
any of certain toothed cetaceans having a blunt or rounded snout; derived from sea hog or hog fish; compare dolphin. Also, to leap clear of the water, as when a speeding boat hits a wave and leaves the surface.

port :
the left-hand side of a vessel or craft when facing forward, and designated by the color red; formerly known as larboard (larborde) or loadboard for the "loading side" set against the wharf. Also, a place with docking facilities for ships to load or unload passengers or cargo, as a "port of entry" or "port of call". Also, an exterior opening or aperture on a craft or vessel for various uses, including portal and porthole.

portage :
to carry a boat and supplies overland from one navigable waterway to another. Also, the route over which such a carry is done.

porthole :
a small, round, window-like opening, usually covered with a hinged watertight glass closure, set into the side of a vessel for admitting air and light.

Poseidon :
the god of the sea and protector of all waters in the Greek religion. After the fall of the Titans, Poseidon was allotted the sea. He was worshiped especially in connection with navigation; but as the god of fresh waters, he was also worshiped as a fertility god. Poseidon was represented as extremely powerful, with a violent and vengeful disposition. He carried the trident, with which he could split boulders and cause earthquakes. When Laomedon failed to pay him for building the walls of Troy, Poseidon sent a sea monster to ravage the Troad and years later vengefully assisted the Greeks in the Trojan War. His grudge against Odysseus is one of the themes of the Odyssey. He was the husband of Amphitrite, who bore him Triton, and by others he fathered many more sons, who usually turned out to be strong, brutal men (like Orion) or monsters (like Polyphemus). In Thessaly and other areas he was important as Hippios, god of horses, and was the father of Pegasus. The Romans identified him with Neptune.

pot :
slang for the hyperbaric chamber used as a sustained environment in saturation diving.

pothole :
a hole cut into submerged bedrock by the erosive action of sand and gravel that's whirled about by eddying water; a more or less cylindrical hole formed in rock by the grinding action of the detrital material in eddying water. Also, a cave opening vertically from the ground surface. [cf: swirlhole, moulin]

abbreviation for polyphthalamide (aka: high performance polyamide), a type of semi-crystalline nylon that's used as a heat resistant metal replacement; under slightly different formulations, this thermoplastic resin is manufactured under trade names Amodel, Grivory, Ultramid T, VESTAMID HTplus, and Zytel.

ppO2 meter / ppO2 meter :
an oxygen-sensitive electro-galvanic fuel cell that automatically monitors and measures the concentration of oxygen in the breathing gas loop of fully closed-circuit re-breather systems so as to detect and adjust the partial pressure mixture.

pressure :
the exertion of force upon a surface by a substance (eg: object, fluid, gas, etc) in contact with it; such a force per unit area is measured by pascal (Pa), newton, pounds per square inch (PSI), pound-force per square inch absolute (PSIA), pound-force per square inch gauge (PSIG), bar, decibar (dbar), millibar (mb), or dyne.

pressure hull :
the inner, pressure-resistant hull of a submarine or other submersible; the crush depth of a submersible is affected as much by the buoyancy of a submersible as by the physical resistance of its pressure hull.

pressure ridge :
a fracture wall produced by the compression of grinding and colliding ice floes.

pressure suit :
an airtight protective suit that can be inflated to maintain approximately normal atmospheric pressure on a person in an aberrant or anomalous environment; also called pressurized suit.

professional diver :
a certified underwater swimmer who is paid for diving, especially military or commercial, salvage or construction/destruction.

promenade deck :
all or part of an upper deck on a ship where passengers can stroll without interfering with shipboard operations.

propeller :
a device having a revolving hub with radiating blades that rotates in a fluid (eg: water, air) for propelling a craft by thrust; made of cast iron or steel, bronze or composite alloy, it's mounted singly before the rudder, or twinned to either side of the keel, having evolved from fixed to variable pitch to achieve constant speed, and counter rotating to balance torque when mounted in multiples; simultaneously invented in 1837 by Swedish-American engineer John Ericsson and English inventor Sir Francis P. Smith to supersede the less efficient paddle wheel.

protozoan / protozoon :
any of various one-celled protist organisms that usually obtain nourishment by ingesting food particles, rather than by photosynthesis: which phyla is classified according to its means of movement, as by pseudopod, flagella, or cilia.

prow :
the forepart of a craft or vessel, designated by the color white; also called bow or stem.

abbreviation for Pounds per Square Inch, a measure that's used to describe the force of pressure acting on a given area; 1 psi approximately equals 6.895 kPa.

abbreviation for Pounds-force per Square Inch Absolute, which is the gauge rating plus sea level atmospheric pressure.

abbreviation for Pounds per Square Inch Difference, which refers to a measurement of the difference between two pressures.

abbreviation for Pounds-force per Square Inch Gauge.

abbreviation for Pounds per Square Inch Sealed Gauge, which measures the difference in pounds per square inch between a chamber of air sealed at atmospheric pressure and the pressure at the measuring point.

abbreviation for Pounds per Square Inch Vented Gauge, which measures the difference between the measuring point and the local pressure.

puddle :
a small pool of water or other liquid. Also, slang for any body of water, regardless of size, used informally as a term of convenient reference. [v: dub]

pulpit :
on smaller ships and other watercraft, a safety rail rising from the deck near the bow, and extending around it.

pumpkin suit :
see exposure suit.

pumpout site :
a facility that pumps out and receives sewage from a holding tank on-board a vessel; also called pumpout station.

purge valve :
an actuator that will clear or empty a device by replacement upon demand, as to vent a regulator of water with a burst of air by manually depressing a plunger.

purl :
to flow with curling or rippling motion, as a shallow stream does over stones. Also, a circle or curl made by the motion of water, as a ripple or eddy; possibly derived from "bubble up" or "gush" [Norwegian 'purla']. Also, to flow with a murmuring sound.

P-valve :
a dry suit accessory that enables a male diver to void his bladder during a dive; consists of a condom-like catheter, which convenience can cause several harmful side-effects. [cf: Texas catheter]

Pyle stops :
the addition of brief decompression stops inserted halfway between the conventional decompression stops when ascending from deep dives; also known as "deep stops" and named after Richard Pyle, who pioneered the methodology.

quarterdeck :
that part of a vessel's weather deck running from midship to the stern or poop deck, and which may have bulwarks.

quay :
a landing place constructed along the edge of a body of water, typically built of solid masonry.

quickwater :
that part of a river or stream having a strong current.

radial flow :
a type of scrubber canister wherein the absorbent carbon dioxide gas flows from the center to the outside.

raft :
a floating platform that's constructed or manufactured of more or less rigid materials that're buoyant, such as a lashed-together assemblage of planks and casks, or an inflatable rubber raft.

raft ice / rafted ice :
ice in cakes or sheets that piles atop or overlaps one another; an ice floe that overlaps another ice floe. Also, an ice floe that transports embedded organic debris (eg: soil, rock, etc) from the shoreline out to sea.

rafting :
the practice of traveling on rivers and streams by raft, as a form of entertainment or sport.

rankine :
an absolute temperature scale with a degree interval equal to fahrenheit. [nb: the degree intervals of the kelvin scale are the same as celsius, as the rankine are the same as fahrenheit]

Raoult's law :
this law states that the addition of solute to a liquid lessens the tendency for the liquid to become a solid or a gas due to a lowering of the concentration of water molecules; quantitatively, the solvent's vapor pressure in solution is equal to its mole fraction times its vapor pressure as a pure liquid, but this mathematical relation is accurate only for dilute solutions; the vapor pressure of mixed liquids is dependent on the vapor pressures of the individual liquids and the molar vulgar fraction of each present in solution; named after F.M. Raoult.

rapid ascent :
a too swift or uncontrolled ascent toward the surface, being faster than the currently recommended rate of 60 feet (18m) per minute, which may be caused by overinflation, poor buoyancy control, being underweight, or panicked.

rapture of the deep :
phrase coined by Jacques Y. Cousteau for nitrogen narcosis.

abbreviation for Residual Bottom Time.

reach :
a straight portion of a river or channel between two bends. Also, a level portion of a canal, as between locks; sometimes called "pound". Also, any continuous stretch or uniform extent of something, as 'a reach of dunes'. Also, a point of sailing in which the wind is within a few points of the beam, either forward of the beam (close reach), directly abeam (beam reach), or abaft the beam (broad reach). Also, to sail with the wind forward of the beam but so as not to require sailing close-hauled.

re-breather / rebreather :
an underwater breathing apparatus that cleanses and recycles captured air back into the air supply; a method of re-using exhaled breath so that it can be re-inhaled, being a self-contained device used to regulate and re-circulate breathing gases so that diving time can be extended and dive functions will be quieter. The closed-circuit re-breathing system (CCR) does not release exhaled gasses as exhaust, but filters and recycles the discharge back into the gas supply, which is accomplished by scrubbing CO2 and adding O2 as necessary to maintain a constant partial pressure of oxygen. The semi-closed circuit re-breathing system (SCR), which also uses a scrubber, releases a portion of each breath into the water while the same portion of new breathing gas is injected into the cycle.

recalculation dive :
a dive where thirds are re-calculated during its course, usually at or near another exit.

recompression :
a repressurization treatment for air embolism or decompression sickness, where an individual is re-introduced to a controlled high pressure environment, as in a decompression or hyperbaric chamber, and gradually returned to normal pressure.

recompression chamber :
a repressurization environment, where atmospheric pressure may be adjusted with selective air mixtures, as used to treat certain diving disorders such as air embolism or decompression sickness.

recreational diving :
swimming underwater with or without breathing aids (snorkel or scuba), as for leisure and enjoyment; also called "sport diving". [nb: many recreational divers do not venture below the 33 foot depth of one standard atmosphere, and most do not venture below the 90 foot depth of two atmospheres, due to the need for mixed breathing gases, decompression stops, and technical training]

red flash :
a red coloration of the lower portion of the sun, occasionally seen as the sun rises above or sinks to the horizon.

red tide :
a brownish red discoloration of marine waters that's caused by a huge aggregation of flagellates and/or dinoflagellates that often produce a potent neurotoxin that contaminates shellfish.

redundancy :
the provision of a duplicate system or of superfluous equipment as a backup, so as to reasonably prevent failure or harm (eg: double inflator, stage bottle, extra light, etc) in the event of loss or failure with a primary.

reef :
a ridge of rocks or sand, often of coral debris, at or near the surface of the water. Also, to make something secure with tie downs. Also, part of a sail that is ("shortened") rolled and tied down to reduce the area exposed to the wind.

reef knot :
a square knot, wherein the ends cross in different directions, coming out alongside the standing parts, which allows the bights to tighten, producing a secure knot that's used for tying things down; also called "flat knot".

regulator :
a scuba diving device that lowers the level of pressurized air, typically to that at sea level (1 ATM); a reduction valve that controls the flow of breathing gas from the reservoir to the mouthpiece. A device on scuba equipment for regulating the rate at which a constant pressure of compressed gas is fed through a breathing tube in proportion to the depth of water.

repeat dive :
any dive whose profile is affected by a previous dive; also called repetitive dive, and typically involves a surface interval delay.

reservoir :
a natural or artificial place where water is collected and stored for use; impoundment. Also, a receptacle or chamber for holding a liquid or fluid. Also, a subterranean accumulation of liquid or gas held in porous and permeable sedimentary rock; pool.

residual bottom time :
additional time to be spent on the bottom when calculating the no decompression limits for a successive dive in a repetitive dive sequence; abbreviated RBT.

residual nitrogen time :
the hypothetical amount of nitrogen absorbed in body tissues after a dive, which is represented by minutes added to the no-decompression limit for a repetitive dive; RNT is an off-gas dive table calculation.

respiration :
the act of breathing or respiring; the inspiratory and expiratory processes; being the inhalation and exhalation of air in the oxidation of organic compounds occurring within tissues and cells, producing energy for cellular processes, and the byproducts of carbon dioxide and water. An exchange of gases between a living organism and its environment.

respiratory arrest :
the cessation of breathing; apnea.

respiratory system :
the organs and tissues involved in drawing oxygen into the body and removing carbon dioxide; in mammals, includes the nasal cavity, pharynx, trachea, bronchi, lungs, and the diaphragm.

reverse block :
when the internal pressure of an air space is greater than the external pressure.

reverse squeeze :
the effect of pressure during ascent on enclosed spaces that contain air (eg: dive mask, dry suit) or body cavities (eg: sinuses, middle ear), which discomfort or pain can be relieved by equalization.

abbreviation for Rigid Inflatable Boat, or Rigid-hull Inflatable Boat; also called a "squidgie".

rigging :
lifting or hauling tackle. Also, the ropes and other lines used on a ship to support the masts and spars, to work the sails and yards.

riptide / rip tide :
a tide that's in opposition to other tides, causing a violent disturbance in the sea; a powerfully channeled current of water that flows away from the shore, through the surf zone, and past the line of breaking waves, which typically occurs where there's an outflow into the surfline or a shoreline of turbulent breakers, dissipating as it moves farther offshore.

risk :
according to numerous surveys conducted in different countries since the proliferation of recreational scuba diving, which is less hazardous than professional diving, underwater swimming is 40-90 times more dangerous than driving an automobile. [cf: parachuting is safer than driving]

river :
a natural stream of water of fairly large size that's flowing in a definite course or channel, or in a series of diverging and converging channels. Also, a similar stream of something other than water, as "a river of lava" or "a river of ice".

abbreviation for Residual Nitrogen Time.

rode :
the line, cable, or chain that secures an anchor. Also, the line or chain that connects a buoy to an anchor.

rogue wave :
an abnormally large wave that occurs on a seemingly random basis in the oceans; this unpredictable sea wave is also known as a freak wave, sleeper wave, sneaker wave, and king wave. Of enormous proportion, great in height and steepness, these unexpected waves sometimes travel in a direction at an angle to the prevailing seas, or occur where waves meet opposing currents.

roll :
axial plunge, swaying or rocking, as of a ship's alternating side to side, port to starboard movement.

roller :
a long, unbroken, swelling wave that advances slowly.

rolling wave :
a long heavy sea wave as it advances toward the shore.

rotameter :
an instrument for measuring the rate of flow of a liquid, consisting of a tapered vertical tube in which a small float is forced upward until its weight balances the fluid force; derived as a partial translation of "rotational measure".

rotten ice :
ice that's pitted or honeycombed from melting.

round turn :
a wrap of rope or line around an object one-and-a-half times so as to reduce the load over a small diameter (less than 3"), or to relieve knot tension by increasing friction.

abbreviation for Remotely Operated Vehicle.

rowboat :
a small open boat propelled by the leverage of an oar, or a number of oars, that's used as a transport or touring conveyance.

rowlock :
see oarlock.

rudder :
a vertical blade at the stern of a vessel that can be turned to change the vessel's direction when the vessel is in motion. Also, any means of directing or guiding a course.

rudderhead :
the upper end of a rudderpost to which a tiller, quadrant, or crossbar yoke is attached.

rudderpost :
the vertical member on which a ship's rudder is mounted; a sternpost.

rule of thirds :
the practice of dividing the volume of air (in cubic feet or psi) into thirds: with one third for the penetration, one third for the exit, and one third for emergency use; also called "thirds".

runabout :
a small motorboat that's used for recreation.

running knot :
a slipknot.

running light :
any of various navigation or warning lights that are required to be displayed by a vessel when operating between sunset and sunrise, or during inclement weather or other low visibility conditions.

running noose :
a loop formed in a cord or rope by means of a slipknot; it binds tighter as the cord or rope is pulled; also called "slip noose".

running rigging :
rigging used for handling sails, yards, and the like; as contrasted with standing rigging. Also, rigging used for handling cargo.

abbreviation for the Sub-Aqua Association.

safety car :
see life car.

safety line :
a line connecting paired divers when visibility is marginal or compromised. Also, a guideline laid temporarily through an entanglement or maze that marks the route and establishes the entrance; this guideline is retrieved by the last diver when exiting. Also, any line rigged on a vessel (eg: lifeline) or from a float (eg: ascent / descent line) for the protection of divers and crew.

safety stop :
a specific period of time spent at a particular depth to assist in nitrogen off-gassing during a dive ascent; a safety stop, which is not mandatory by definition, should still be performed even within no decompression limits.

Saffir-Simpson scale :
a scale indicating the speed or pressure of cyclonic storms, enumerated 1-5, and commonly expressed as "Category #" [ie: Category 1: 65-82 kts/74-95 smph @ 980 mb/28.94" hg; Category 2: 83-95 kts/96-110 smph @ 965-979 mb/28.50-28.91" hg; Category 3: 96-113 kts/111-130 smph @ 945-964 mb/27.91-28.47" hg; Category 4: 114-135 kts/131-155 smph @ 920-944 mb/27.17-27.88" hg; Category 5: +135 kts/+155 smph @ 919 mb/27.16" hg]; also cited as "Safford-Simpson Scale".

sagging :
the behavior of a ship when only its bow and stern are supported by wave crests, leaving the midships area unsupported in the trough.

sailor :
a seaman or seafarer; also called swabby, squid, gob, anchor clanker, or old salt.

sailor dive / sailor's dive :
a head-first plunge into water with the diver's body fully extended while their hands and arms remain at their sides.

Saint Adjutor :
venerated in the Latin church as the patron saint of swimmers, boaters, and drowning victims; also known as Adjutor of Vernon. As a knight in the First Crusade, he escaped Muslim persecution and captivity by calming the sea with holy water and the sign of the Cross before swimming away in his chains; he became a hermit in his later life.

Saint Christopher :
the "Christ-bearer" was once a saint and martyr of the Greek and Latin churches, but the patron saint of travelers was dropped from the liturgical calendar in 1969; he was the protecting saint against floods, fires, and earthquakes, and his image was believed to keep the viewer from harm.

salinity :
the degree or proportion of a saline solution, including mineral and chemical salts.

sally ship :
to cause a vessel to list alternately from side to side by shifting crewmembers or a party of passengers back and forth across its main deck so as to free a grounded hull by altering its trim, enabling a stranded vessel to withdraw.

salt water aspiration syndrome :
a reaction in the lungs that's caused by inadvertently inhaling a mist of sea water, especially from a faulty demand valve.

salty :
to be sharp, witty, or piquant. Also, to be vulgar or coarse. Also, to be ship shape or squared away. Also, to be experienced or knowledgeable, be "handy as an old salt".

salty dog :
any item lost or destroyed during operations at sea. Also, slang for an experienced or knowledgeable person, as an "old salt" or "sea dog". Also, a cocktail of gin or vodka mixed with grapefruit juice that's served (like a margarita) in a salt-rimmed glass.

salvage :
saving a ship or its cargo. Also, saving anything from shipwreck, fire, or other danger or peril; as to retrieve, recover, or rescue. Also, compensation given to those who save a ship or its cargo.

sand bar :
a mass of sand formed in a river or sea by the action of tides or currents, often as an obstruction to navigation.

saturation :
the complete uniting, by solution or combination, of one substance with another; to impregnate or imbue thoroughly; the degree to which a gas is dissolved in the blood or tissues.

saturation diving :
diving performed after the body is fully saturated with nitrogen, which is a much longer time period underwater than is permitted in recreational diving tables; a decompression regime that enables commercial divers to maintain high pressure gas levels in their tissues so as to work underwater for weeks.

sault :
a waterfall or rapid of frothy water running over shoals; as derived from 'leap'.

scantling :
a dressed timber of relatively slight width and thickness, or a rolled metal member of similar dimensions, used for support or framing in a vessel. Also, the dimension, in cross section, of a framing member; as derived from a small quantity or amount (scant, gauge).

scooter :
slang for a diver propulsion vehicle (DPV).

scow :
any flat-bottomed vessel with a rectangular hull and sloping ends, such as a barge, sailboat, rowboat, johnboat, dory, punt, gondola, dinghy, or skiff; as derived from "ferryboat".

abbreviation for Semi-Closed Circuit Re-breather.

screw :
slang for propeller (qv).

Scripps Institution of Oceanography :
a research facility, established 1901 and transferred to the University of California at La Jolla in 1912, which maintains several ships and marine laboratories to conduct studies; in 1952, it became the first North American center to instruct civilians on the proper use of scuba equipment, which program was transferred to the Los Angeles County Department of Parks and Recreation in 1954, and then to the YMCA (ie: Underwater Instructor Certification Course) in 1959.

scrubber :
an integral component of a re-breather system containing a chemical that reacts with exhaled gas to remove carbon dioxide (CO2).

acronym for Self Contained Underwater Breathing Apparatus; a portable breathing device for free-swimming divers. An experimental underwater breathing system was first employed by Dr. Freminet in 1772. In 1825, a helmeted "diving dress" with a self-contained air tank was introduced by William James. The double-hosed "aqua-lung" was invented (1942) during WWII by Emile Gagnan and Jacques Y. Cousteau.

scuba orienteering / scuba-o :
a competitive underwater sport wherein scuba divers swim a designated circuit that's marked by buoys while using compass navigation and mechanical distance measurement devices; points are awarded for speed and accuracy in completing the defined course without surfacing.

scuba tank :
see tank, cylinder, bottle.

scud :
to run quickly or move hurriedly, as wind driven clouds or mist. Also, to run a boat or ship before a gale with little or no sail set.

scull :
an oar mounted on a fulcrum at the stern of a small boat that's moved from side to side (sweep) so as to propel the boat forward in the water. Also, either of a pair of oars rowed by one rower. Also, a boat propelled by an oar or pairs of oars, especially a narrow, light, racing boat containing up to four rowers, each of whom is equipped with a pair of oars.

scupper :
a drain situated at the edge of a deck that's exposed to the weather, allowing accumulated water to debouch into the sea or into the bilges.

scuttle :
a small hatch or port, or its hatchway cover, located in the top, sides, or bottom of a vessel. Also, to deliberately sink something, or to intentionally ruin or destroy something.

abbreviation for Scuba Diving International, being a non-technical qualification agency created in 1999 by Technical Diving International (TDI).

sea :
the salt waters that cover the greater part of the earth's surface, the subdivisions of which are more or less definitely marked off by land boundaries (eg: North Sea, Ross Sea, Bering Sea, Coral Sea, Mediterranean Sea, etc). Also, one of the seven seas; ocean. Also, a large lake or landlocked body of water. Also, the degree or amount of turbulence of a body of water, as caused by the wind. Also, a large wave, or the waves. Also, the work, travel, and shipboard life of a sailor.

sea anchor :
any of various devices, such as a drogue or buoy, that are dropped overboard at the end of a cable, causing resistance to movement of the hull through the water, so as to decrease speed and/or increase stability while holding the bow of a vessel into the wind.

seabed :
the seafloor (qv).

sea change :
a major transformation or alteration, especially a striking one brought about by the weather at sea.

sea chest :
a container for holding personal belongings aboard ship.

seacock :
a valve in the hull of a ship for admitting sea water into some internal chamber, as for ballast.

sea daddy :
slang for a sailor's mentor or sponsor.

sea deck :
a fixed stern platform positioned at sea level that's separated from the main deck by a transom; also called a "dive step" or "dive platform", this diving deployment platform is often rigged with a 'granny line' or 'gerry line' to assist in the recovery of swimmers back onto the boat. [nb: not to be confused with 'well deck' or 'diving stage']

sea fence :
a durable mesh suspended from a cable that's strung between buoys so as to isolate or confine a select area, usually for protective purposes; extending to the seafloor, the mesh is typically sized to permit the passage of fishes, but not people.

seafloor :
the solid surface underlying a body of water; also called seabed.

sea gate :
a navigable channel giving access to the sea.

sea legs :
the ability to adjust one's sense of balance to the constant motion of a ship at sea, especially while remaining free of seasickness.

sea level :
the surface of the sea at a mean horizontal plane between high and low tides. [nb: the curvature of the earth restricts visibility at sea level to only three nautical miles (3nm)]

seaman :
a sailor or seafarer; also called swabby, squid, gob, anchor clanker, or old salt.

seamount :
an undersea mountain rising prominently above the seafloor but having its summit well below the surface of the water; also known as tablemount. [nb: not tableland]

seaplane :
a fixed-wing or rotary-wing aircraft fitted with hydrofoil floats for take-offs and landings on the surface of the water.

seaport :
a port, harbor, or anchorage that accommodates seagoing vessels.

sea room :
unobstructed space at sea in which a vessel can maneuver.

seashore :
land along the sea between the ordinary high-water and low-water marks; shore.

sea smoke :
a steam or evaporation fog that's formed when water vapor is added to air which is much colder than the vapor's source, most commonly when very cold air drifts across relatively warm water; also called "water smoke", "arctic sea smoke", "antarctic sea smoke", and "frost smoke".

seasonal thermocline :
a temperature gradient in a body of water that's not affected by the diurnal changes in surface forcing; in general, it is established each year by heating of the surface water in the summer, and is destroyed the following winter by cooling at the surface and wind-driven mixing.

sea wall :
a strong wall or embankment that serves as a breakwater, or is used to prevent the encroachments of the sea.

second-foot :
a unit of measure for liquid flow, especially of rivers, being equal to one cubic foot per second. [nb: one cubic foot of water weighs approximately a quarter of a ton]

second mate :
the officer of a merchant vessel who's next in command and responsibility beneath the first mate; also called 'second officer'.

second stage :
the second phase of pressure reduction by the regulator assembly, set to deliver low air pressure from the medium pressure of the first stage of the regulator to the breathable air at the mouthpiece.

seiche :
an occasional but sudden oscillation of the water in a lake, bay, estuary, reservoir, or other containment that produces fluctuations in the water level, which are caused by wind, earthquakes, landslides, avalanches, changes in barometric pressure, and so forth.

semi-closed circuit re-breather :
a re-breather that continuously vents a small amount of excess gas from the system while the breathing gas is injected at a constant rate to the diver. Semi-closed circuit equipment generally supplies only one breathing gas (eg: air, nitrox, or trimix) that has a maximum operating depth that is safe for the depth of the scheduled dive. The oxygen mixture must be carefully chosen to avoid toxicity or hypoxia as the work rate of the dive changes. Semi-closed circuit equipment, which is fairly simple and inexpensive, provides good underwater duration for military and recreational divers.

semi-dry suit :
a wet suit with wrist and ankle seals to reduce the entry and exit of water.

service float :
a floating structure equipped to supply oil, fuel, water, sewage pumpout, and other related services to boats.

service pressure :
the pressure at which a device is rated to work; not the test or hydrostatic pressure.

set and drift :
the tangential deflection of a ship from its intended course under the influence of wind and current, with 'set' being the direction of that deflection, and 'drift' being the speed in knots of the displacement.

sextant :
an astronomical instrument used at sea to determine latitude and longitude by measuring angular distances, especially the altitudes of the sun, moon, and stars; as derived from the "sixth part of a unit".

shallows :
the shallow part of a body of water; shoal.

shark pod / shark prod :
a handheld device carried by a diver that's intended to repel a shark by administering an electrical field pulse; also known as a "shark punch" or "shark shield".

sheer :
to swerve or deviate from a course, as a divergence. Also, in shipbuilding, the fore-and-aft upward curve of the hull of a vessel at the main deck or bulwarks. Also, the position in which a ship at anchor is placed to keep it clear of the anchor. Also, any very steep perpendicular or vertical extension; precipitous.

sheet :
a thin line, cord, or wire used in reeving tackle and the rigging of sails [nb: like a hawser, it is never called a rope]. Also, a sail on a boat or ship.

shell :
a long, narrow, lightweight boat used for rowing by one or more persons, especially when racing. Also, any hard protective case, or an enclosing cover, as in imitation of the crust-like exterior of some plants and animals. Also, the plating or planking forming the exterior hull of a ship.

shellback :
an experienced sailor, especially someone who has crossed the equator and undergone the arcane rites of Neptune; also called a sea dog, old salt, or mossback.

shell door :
a water-tight or pressure-resistant opening in the hull of a ship, or in the chamber of a moored platform, that admits limited access (surface or subsurface) to the hollow interior for staging, docking, and associated tasks.

shelter deck :
a weather deck covering a space that's not considered to be fully watertight. Also, the 'tween deck beneath this weather deck.

shingle :
small waterworn stones or pebbles. Also, the area, such as a beach or riverbed, where these small stones or pebbles wash up, lying in a loose mass.

shipmate :
a companion or comrade who serve together on the same vessel; often extended in camaraderie to any seaman or sailor in the "brotherhood of the sea".

ship's complement :
persons permanently assigned to a ship, its permanent party or staff, as distinguished from those temporarily on-board for transport or a cruise; often misspelled "ship's compliment".

shipshape :
everything in proper order, trim and tidy; also called snug or salty.

shiver :
to shake, quiver, quaver, or tremble with chill ("the shivers"), being an involuntary physiological response of muscular contractions that are intended to increase the lowered body temperature with activity. Also, the shaking of sails on a vessel headed too close to the wind.

shoal :
a place where the depth of water is shallow, especially where the seafloor (eg: sandbank, sand bar) is visible at low tide. Also, a large number of things, as a school of fish or throng of people.

shore :
the land along the edge of a sea, lake, or river, including a beach, tideland, or shoal; especially a 'seashore', being that ground between the ordinary high-water and low-water marks. Also, a supporting post or beam, a prop or strut, especially one braced against the side of a building or a ship in drydock.

shore diving :
scuba diving that starts (and finishes) from the shoreline; ground-level entry into and exit from the water.

shoreline :
that line where the shore and water meet.

shot :
a unit of measure for anchor chain equal to 15 fathoms (90 feet, 27m). Also, an obsolete unit of measure equal to a league (3 nautical miles or 4.8km); as derived from 1.5 Roman miles, which seems to be the origin of the conventional claim for a three-mile limit of territorial waters extending offshore. [nb: 12 inches = 1 foot, 3 feet = 1 yard, 6 feet / 2 yards = 1 fathom, 16.5 feet = 1 rod (aka: pole or perch), 66 feet / 4 rods = 1 chain (90 feet / 15 fathoms = 1 anchor chain), 10 chains / 660 feet (1/8 statute mile) = 1 furlong, 120 fathoms / 720 feet = 1 land cable, 101 fathoms / 606 feet (1/10 nautical mile) = 1 cable, 3 statute miles = 1 land league, 3 nautical miles = 1 sea league / shot]

shot line / shotline :
a rope suspended in the water from a buoy or float that's weighted at its trailing end so as to hang vertically without touching the seafloor, as used for decompression stops.

shove-off :
to launch (as in "launch the boat") or to execute (as in carry-on), sometimes expressed as castoff. Also, slang for leave / depart or go away / get away / get out.

showboat :
anyone or anything that stands-out; anything done more for attention than for practicality or function, as a show-off or razzle-dazzle. Formerly a flamboyantly theatrical steamboat.

SI :
abbreviation for Surface Interval. Also, the abbreviation for the International System of [physical] Units, which includes meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity).

side-mount :
an equipment configuration wherein the air tanks are attached to the side of the diver, between the arms and torso, which arrangement is used for low bedding plane passages with very little vertical clearance, a situation where the back-mount configuration is problematic.

signal flag :
a small cloth panel, distinctively colored and patterned, used to post messages or notices on a ship's superstructure; also called burgee or pennant.

significant wave :
in ocean wave forecasting, a fictitious wave with a size and interval equal to the average height and period of the highest one-third of actual waves that pass a fixed measuring point. The generation of waves on water does not result in a uniform wave height, but in a spectrum of waves distributed from the smallest capillary waves to the largest freak waves; within this spectrum there is a finite possibility of each of the wave heights to occur, with the largest waves being the least likely (only 1 in 1000 waves will be nearly double the significant wave height or higher). The wave height most commonly observed and forecast is the "significant wave height", which is defined as the average of the one third highest waves.

silt-out :
a complete loss of visibility caused by the turbidity of disturbed silt, typically from careless finning.

single berth :
a mooring that accommodates one boat, with a finger pier on each side of the berthed vessel.

single-day :
a dive series with a surface interval of less than 24 hours between consecutive dives; a single day of diving, regardless of the number of dives completed in that period; juxtaposed to multiday.

singles :
the use of only one air cylinder when diving.

sinkhole :
a hole formed in soluble rock by the action of water, which serves to conduct surface water to an underground passage. Also, a depressed area in which drainage, waste, or debris collects; pan.

siphon :
a tube or pipe that uses atmospheric pressure to draw liquid from one level to another, especially when mechanically transferring the contents of one container to another. Also, an outlet or drain in the bedrock or seafloor that draws water into a lower level pool or chamber; as opposed to a spring or seep. Also, a projecting tubular part of some animals through which liquid enters or leaves their body, such as mollusks, chitons, squids, and octopuses.

skeg :
any flat protrusion or projection on the outside of the hull supporting a rudder at its lower end, located abaft a sternpost or rudderpost. Also, an extension of the keel of a small craft that's designed to improve steering; as derived from cutwater.

skiff :
any of various types of boats small enough for sailing or rowing by one person.

skimmer :
slang for a Boston whaler, shaped like an elongated rowboat but mounting an outboard motor. Also, slang for any sailor aboard a surface ship or boat, for behavioral similarity to gull-like birds that feed from sea level.

skin :
informal term for a thin exposure suit, typically made of spandex (eg: Lycra) or other polyurethane fabric, that's used in warm water diving; may also be worn under a wet suit; also called "skin suit".

skin diving :
free-breathing and free-swimming underwater diving, often performed with only a face mask and flippers, without a protective suit or supplemental air; elapsed time and depth are determined by breath-hold duration.

skin suit :
informal term for a thin exposure suit, typically made of spandex (eg: Lycra) or other polyurethane fabric, that's used in warm water diving; may also be worn under a wet suit; also called "skin".

slack :
not tight, taut, firm, or tense; lax or loose. Also, slow, sluggish, or indolent; as when the wind, water, or tide is moving very slowly. Also, the part of a rope, sail, or the like, that hangs loose, without strain upon it. Also, a cessation in a strong flow, as of a current at its turn. Also, negligent; careless; remiss.

slack water :
water that is free of currents, especially a body of water that's between tides. Also, the time period when water is between tidal currents, as at the cessation of flow when a current turns.

abbreviation for Scuba Lifesaving and Accident Management, a YMCA diver rescue course.

sleeper wave :
see sneaker wave, rogue wave.

sling / sling-eye :
a strap, band, or the like, forming a loop by which something may be suspended or carried. Also, a rope, chain, net, or the like used for hoisting cargo, or for holding it while being hoisted. Also, a chain for supporting a hoisting yard.

sling bottle :
see stage bottle.

slings :
the middle area of a hoisting yard where the hoisting chains are attached.

slingshot valve :
see Y-valve.

slip :
a space in a dock, or between two wharves for a vessel to lie in; a berth. Also, an inclined plane, sloping to the water, on which vessels are built or repaired.

sludge :
a deposit of mud, mire, or ooze at the bottom of a body of water. Also, any of various sediment deposits or mixtures of finely powdered substances with some type of liquid. Also, a slurry of broken ice floating on the sea. Also, slang for strong coffee.

slue / sluing :
to turn or swing around, especially when pivoting or rotating about its own axis.

sluice :
an artificial channel for conducting water, sometimes surplus, often fitted with a gate ("sluice gate") for regulating the flow; also called a sluiceway. Also, to flush or cleanse something with a rush of water; as derived from "exclude".

slurry :
a thin mixture of an insoluble substance suspended in a liquid.

slush :
partly melted snow. Also, liquid mud; watery mire. Also, waste or refuse, especially from cooking. Also, a mixture of grease and other materials used for lubrication.

abbreviation for Surface Marker Buoy.

smuggler's trap :
a compartment or well aboard ship, usually concealed, that's used to hide transported contraband, from munitions to medicines, including persons, so as to avoid confiscation or taxation; being a temporary stash, hidey-hole, or hideaway, wherein 'trap' derives from "suitcase" and not "contrivance".

snaking :
netting stretched between the BULWARK and LIFELINE, or between the GUNWALE and footrope on a vessel to prevent objects (including people during storms) from falling overboard.

sneaker wave :
an exceptional wave that's much higher and steeper than the waves in an average series of rollers, even on a calm day of unspectacular breakers, and because it's unpredictable, its turbulent appearance is unavoidable and surprising to small craft boaters and off-shore swimmers, surf casters and shoreline climbers, beachcombers and coastal trekkers; also known as rogue wave, freak wave, sleeper wave, and king wave.

snorkel :
a J- or S-shaped tube through which a swimmer can breathe while moving at or near the surface of a body of water; often used while skin diving.

snowblink :
a white luminosity on the underside of clouds that's caused by the reflection of light from a snow surface; also called "blink", as derived from 'blink' meaning gleam, twinkle, glitter, or shine.

snub :
to suddenly stop a moving rope by cinching it up against a solid object; to abruptly check the paying-out of a running line by making it fast to a fixed point. Also, to halt the movement of an object or craft by securing it with a fixed tether.

snubber line :
rope used to check a vessel's way when being warped into a dock or basin.

snuba :
a portmanteau word, joining SNorkel and scUBA, that's used to designate an introductory experience of underwater swimming with close supervision that doesn't involve training or certification. The swimmer, who is tethered to a dive certified guide, uses the regular mask, fins, and weight belt, but the mouthpiece is connected to a long hose that feeds air from a series of tanks or a compressor on the surface. This tandem dive experience, with the least amount of paraphernalia, introduces the novice to the underwater world without intimidation. A raft with outboard handles is often used as the dive platform to increase the swimmer's confidence. This method is a popular initiation for tourists visiting the tropics, and is usually restricted to protected areas, where wind, current, and waves are negligible. These escorted dives are usually brief and are limited to depths no greater than 20 feet.

snug :
a trim, tidy, or compactly arranged ship or its parts; shipshape. Also, a compact and confined harbor or anchorage. Also, to lie closely together; to nestle closely.

solo diving :
the practice of diving underwater without a partner, which activity is not recommended and is not permitted on charter boats; at a minimum, the availability of an alternate air source is recommended.

soniferous / sonify :
conveying or producing sound, as a "sonified layer" or an "ensonified area"; obstructed or obscured by turbulence.

sound :
a relatively narrow passage of water between larger bodies of water, or between the mainland and an island. Also, an inlet, arm, or recessed portion of the sea. Also, to measure or try the depth of water at sea by letting down a lead or plummet at the end of a line, or by some equivalent means. Also, to examine or test the seafloor or the bottom of a deep hole with a lead that brings up adhering bits of matter. Also, to go down (to touch bottom) or to plunge downwards; to dive. Also, to seek, fathom, or ascertain by examination or investigation. Also, the sensation produced by stimulation of the organs of hearing by vibrations transmitted through the air or some other elastic medium, which travel at approximately 12miles/minute through air and 52 miles/minute through water; the particular auditory effect produced by a given cause. [nb: the velocity and distance that sound travels in either air or water depends upon atmospheric pressure, medium temperature, molecular density, and turbulence; such that under equivalent conditions, sound moves faster in salt water than in fresh, faster in fresh water than in air. The audible range of sound wave frequencies for humans is 20 - 20,000 Hz; above which ultrasonic waves may be felt, instead of heard.] [cf: ultrasound]

spar :
a stout pole, such as a mast, yard, boom, gaff, or the like.

spar deck :
the upper deck of a vessel, extending from stem to stern.

spear gun :
a device for shooting (by compressed air, recoil springs, or elastic bands) a barbed missile under water, with or without an attached trailing line.

spew :
foam, froth, or scum that's been discharged or ejected, as "spew forth".

abbreviation for Submersible Pressure Gauge.

spherical sailing :
a method of navigation in which the curvature of the earth is taken into consideration when plotting a course; also called "circular sailing".

spicule :
one of the small, hard, calcareous or siliceous bodies that serve as the skeletal elements of various marine and freshwater invertebrates; also known as sclerite. Large spicules, visible to the naked eye, are referred to as megascleres, while smaller microscopic ones are termed microscleres.

spindrift :
spray swept along the surface of the sea by a violent wind.

spit :
saliva or spittle, as a natural secretion ejected or expectorated onto the window of the diving mask to prevent fogging. Also, a narrow point of land projecting into a body of water. Also, a long narrow shoal extending from the shore. Also, any of various rods, pins, or the like used for particular purposes.

splash :
slang for an underwater dive.

splice :
to join rope together by darning or interweaving strands with a marline spike or awl; to repair or reinforce rope by interweaving strands. Also, to unite timbers or conjoin spars by overlapping and binding their ends.

split fins :
a set of flippers or fins that work like an underwater propeller.

sport diving :
swimming underwater with or without breathing aids (snorkel or scuba), as for leisure and enjoyment; also called "recreational diving". [nb: many sport divers do not venture below the 33 foot depth of one standard atmosphere, and most do not venture below the 90 foot depth of two atmospheres, due to the need for mixed breathing gases, decompression stops, and technical training]

spray :
droplets of water that are broken-up and blown or cast into the air. Also, any liquid or other material in particle form that's discharged into the air.

spread-eagle jump :
see giant stride entry.

spring suit :
a rubber or neoprene wet suit that covers the diver's torso, having short sleeves and long or short legs, as worn in temperate climes.

spud can :
slang for the foot on a leg of a jack-up rig, which is designed to spread the load so that the platform doesn't sink too deeply into the seafloor.

spume :
foamy matter floating on a liquid, as froth churned by a turbulent sea.

squall :
a sudden violent wind, often accompanied by rain, snow, or sleet; as derived from "shriek". [nb: regional variants include Abroholos, Barat, Borasco, Brubu, Chubasco, Churada, Papagayo, Suestado, Sumatra, Tehuantepecer, and the like]

square away :
to prepare something for inspection or operation; to get organized or ready for something, such as a drill or evolution.

squared away :
someone who is smart or capable; something that performs well, is responsive and effective.

square dive / square diving :
a dive profile wherein the diver descends immediately to full depth, then remains at that level for the duration until resurfacing. This profile is approximately rectilinear when plotted in a coordinate system, where one axis is depth and the other is duration; juxtaposed to multilevel dive / multilevel diving.

squat :
the tendency of a motorcraft or vessel to draw more water astern when in motion forward than when stationary or halted. Also, a thing of little or no value, as naught or nothing, rush or zilch, cipher or nullity, zip or zero. Also, the minimum amount or degree, as the least bit.

squeeze :
the effect of pressure during descent on enclosed spaces that contain air (eg: dive mask, dry suit) or body cavities (eg: sinuses, middle ear), which discomfort or pain can be relieved by equalization. Also, the experience of a diver going through a narrow passage, small opening, or constriction.

squeezer :
see gaiter.

squid :
slang for a seaman or sailor; also called swabby or gob.

abbreviation for Scottish Sub-Aqua Club, organized in 1953 to instruct and govern recreational scuba diving in Scotland.

abbreviation for Scuba Schools International, formed in 1970, which merged with the National Association of Scuba Diving Schools (NASDS) in 1999.

stage :
the platform of the elevator used to transport hard hat or hard suit divers to the deep-sea floor, to recover them and any small objects; also called "diving stage", and derived from "standing place".

stage bottle :
the secondary scuba cylinder that is used to carry different gas mixtures for consumption during various phases of decompression, as used by technical divers. Also, a tank used to carry extra breathing gas so as to extend dive time; also called "sling bottle".

staged decompression :
regular timed stops at particular depths during ascent to allow for nitrogen off-gassing; the prescribed safe rate of ascent for off-gassing a diver is 30 feet per minute while rising to the surface.

stainless steel :
chromium-based alloys of steel that have been variously formulated to resist heat, corrosion, and other deficiencies of unaugmented steel; a high strength ferrous metal that "stains less" than regular steel. [eg: 304 is a versatile grade of stainless steel that has excellent forming and welding characteristics; 316 is a marine grade of stainless steel that's highly resistant to pitting and crevice corrosion in chloride environments]

stanchion :
an upright bar, beam, post, or support, as used when securing or supporting something.

standard atmosphere :
a standard unit of atmospheric pressure, having a value of 1013.2 millibars, of 29.9213 inches, or of 760 millimeters of mercury. Also, an arbitrarily determined vertical distribution of atmospheric pressure, temperature, and density, which is assumed to have physical constants that conform to parametric equations, as used for certain scientific calculations (eg: the design of pressure altimeters).

standard diving dress :
the typical dry suit worn with hard hat diving.

standing rigging :
rigging on a boat that remains permanently in position as a means of steadying various spars, shrouds, stays, and the like; as contrasted with running rigging.

starboard :
the right-hand side of a vessel or craft when facing forward, and designated by the color green; formerly known as steerboard for the "steering side".

stateroom :
a private room or compartment on a ship, or other conveyance.

stay :
any of various strong ropes or wires for supporting, securing, or steadying masts, funnels, and the like; also represented as stayed or stay∑ing, as derived from "to hold in place". Also, something used to support or steady a thing, as a prop or brace; a strip or rod used to stiffen or strengthen. Also, to put a sailing ship on the other tack; to change to the other tack.

steam fog :
fog formed when water vapor is added to air that is much colder than the vapor's source, most commonly when very cold air drifts across relatively warm water. No matter what the nature of the vapor source, the water vapor, upon becoming mixed with and cooled by the cold air, rapidly condenses. It should be noted that although advection of air is necessary to produce steam fog, it differs greatly from an advection fog in the usual sense, which is caused by warm, moist air moving over a cold surface. Steam fog is commonly observed over lakes and streams on cold autumn mornings as well as in polar regions. It is sometimes confused with ice fog, but its particles are entirely liquid. Steam fog is also called "sea smoke", "arctic sea smoke", "antarctic sea smoke", "frost smoke", "water smoke", "sea mist", and "steam mist".

stem :
an upright at the forward part of a vessel into which the side timbers or plates are jointed, designated by the color white; also called bow or prow.

stenobathic :
freshwater or marine life that can tolerate limited changes in depth; as opposed to eurybathic.

stern :
the back or rear of a craft or vessel; designated by the color black.

sternpost :
an upright member rising from the after end of a keel; a rudderpost or propeller post.

storm :
a disturbance of normal atmospheric conditions that manifests itself by strong or heavy winds, and often accompanied by rain, thunder and lightning, snow, hail, or sleet. Alternatively, either an instance of heavy precipitation (eg: rainstorm, snowstorm) unaccompanied by strong winds, or a sudden and violent wind (ie: windstorm) alone.

storm warning :
a showing of storm signals subsequent to an alert notification of severe winds and threatening weather, especially cyclonic conditions [nb: Tropical Depression: 20-34 kts/23-39 smph; Tropical Storm: 35-64 kts/40-73 smph; Hurricane: 65+ kts/74+ smph]. [nb: due to axial tilt during earth's rotation, the hemispheric seasons are not the same length, with the southern summer / northern winter being the shortest season, and northern summer / southern winter being the longest]

strainer :
slang for the sieve-like obstruction in a waterway that sifts objects and debris from the flow, often occluding the flow by accumulation; a hazardous trap that can drown the unwary.

strait :
a narrow passage of water connecting two larger bodies of water. Also, an isthmus or neck. Also, a position of difficulty, distress, or need.

strake :
a continuous course of hull planks or plates on a ship.

stream :
a body of water of indeterminate size that flows in a channel or watercourse, such as a river, rivulet, freshet, brook, rill, run, streamlet, or runnel. Also, a steady current or continuous flow in water, as in a river or the ocean. Also, to place an object in the water at the end of a line that's attached to a vessel; trawl.

streamline / streamlined :
designed or organized so as to engender maximum efficiency; to alter in order to render more efficient or to make as simple as possible. Also, a teardrop line of contour offering the least possible resistance to a current of air, water, or the like; optimally shaped for the most effective motion or conductivity.

streamline flow :
the flow of a fluid past an object such that the velocity at any fixed point in the fluid is constant, or varies in a regular manner; the predictable path of suspended particles that are moving steadily and without turbulence in a fluid medium past an object. [cf: turbulent flow; v: hydrodynamics, fluid dynamics]

strobe :
a high-intensity light with a variable frequency flash, as used in signaling and photography.

subcutaneous emphysema :
an abnormal distention of skin tissue by air or other gas; also called subdermal emphysema.

sublittoral :
of or pertaining to the biogeographic region of the ocean bottom between the littoral and bathyal zones; from the low water line to the edge of the continental shelf, or to a depth of approximately 660 feet. Also, situated in the zone of a lake extending from the lowest depth of rooted photosynthetic plants to the level at which the photosynthetic rate of flora equals the respiration rate.

submarine :
a vessel that can be submerged and navigated under water; also known as sub, guppy, pig boat, boomer, sewer pipe, clockwork mouse, and the like.

submergence recovery vehicle :
an air-transportable deep-sea submarine; abbreviated SRV.

submersible :
a boat or other vessel that's capable of submerging and operating under water, such as a submarine. Also, a device designed for underwater work or exploration, such as a bathyscaphe.

submersible pressure gauge :
a meter, either analog or digital, that monitors and displays the amount of air pressure remaining in the scuba cylinder; a required item of scuba gear that monitors air supply during the course of a dive.

subsurface :
below the surface, especially that of a body of water.

suicide clip :
a hardware device with a spring-loaded angular gate, which can inadvertently engage and attach a diver to an underwater object, or can accidentally disengage from a guideline or other connection; also called "boat clip" or "marine snap link".

sunami :
misspelling of tsunami (qv).

sunshade :
a fly or awning that's been rigged with scantling over an open deck to provide protection from the intensity of direct sunrays, also called bimini top.

super saturation :
an unstable situation where the pressure of a gas dissolved in the blood or tissues is higher than the ambient pressure of that gas.

supralittoral :
pertaining to the region of a lake or ocean shore that is above the shoreline but is often damp from spray or capillary action of the water.

surf :
the swell of the sea that breaks in a foamy mass or line upon a sloping shore or upon shoals. Also, to float (surfing) or swim (body surfing) on the crest of a wave toward shore.

surface detection aid :
any device that's carried by a diver to help maintain contact with the dive boat or to enable the diver to attract attention when injury or dislocation requires rescue at sea; items include strobe, flare, dye marker, flag, SMB, whistle, EPIRB, and the like.

surface interval :
a period of time spent on the surface between dives, especially a delay between repeat dives; abbreviated SI.

surface marker buoy :
a float that may be fixed or towed denoting a dive site, to which an ascent line may be attached, and which may be used as a safety device to warn when divers are swimming underwater; abbreviated SMB.

surface supplied compressed air diving :
underwater diving with the breathing air continuously supplied by an air hose from a compressor on the surface, which can be used for both professional and sport diving.

surfactant :
an active substance produced in the lungs to reduce surface tension in alveoli and small airways, and that coats the lungs to prevent their collapse.

surfline :
the offshore line where the mass of the sea breaks against a shallow or sloping shore, creating foamy breakers from the tidal current that advance inland.

swabby :
slang for a seaman or sailor; also called squid or gob.

sweep :
a large oar sometimes used in small vessels so as to assist the rudder or to propel the craft by a curving movement or swinging stroke. Also, the steady, driving motion of something, as of the wind or a current, especially when continuous. Also, to thoroughly observe or extensively search an area, as in a wide circuit. Also, to conduct an underwater search by towing a drag under the surface of the water.

swell :
a long and unbroken wave, or a series of such "rollers".

swimfin :
one of a pair of paddlelike devices, usually made of rubber, that are worn on the feet as an aid in swimming and scuba diving; imitative of the broad flat limbs or the membranous organs of aquatic animals that are used for steering and propulsion; also called fin or flipper.

swim ladder :
a temporary boarding ladder (qv) that's hung over the side of a boat from the gunnel / gunwale for the ready recovery of swimmers out of the surrounding water; typically flexible (like a Jacob's ladder) for convenient stowage.

swim mask :
a device consisting typically of a transparent glass or plastic panel fitted into a flexible rubber gasket that fits snugly around the eyes, over the cheeks, and usually over the nose; also called "face mask" or "diving mask", as used by scuba and skin divers.

swim platform :
see sea deck.

swimsuit :
a garment worn for swimming or for recreational activities in and around water; also called swimming suit or bathing suit.

swirlhole :
a more or less circular hole that's been eroded in the rock of a streambed (present or past) by eddying water, with or without the mechanical action of sediments up to the size of cobblestones. [cf: pothole]

tables :
decompression tables; also called dive tables.

Table 6 :
the most common treatment procedure for decompression sickness as outlined by the U.S. Navy; consisting of oxygen breathing with air breaks at a maximum pressure of 2.8 ATA with typical treatment times of 285 minutes.

tackle :
any specialized apparatus, equipment, or gear, including rigging. Also, a leverage system of pulleys.

tadpole :
nickname for a frogman trainee.

taffrail :
the upper part of the stern of a ship. Also, a safety rail above the stern of a ship.

tank :
slang for the steel or aluminum cylinder of pressurized breathing gas that's used in scuba diving; also called "bottle".

abbreviation for Total Bottom Time.

abbreviation for Technical Diving International; a certification agency for the technical aspects of recreational scuba diving.

abbreviation for Total Dive Time.

technical dive / technical diving :
an underwater dive deeper than 132 feet (40.2m) using a breathing gas other than compressed air, and requiring at least one decompression stop during ascent. This category also encompasses overhead dives, and the use of special training or equipment.

tekkie / techie :
a technical and gadget oriented diver ... the more the better! A tekkie dive profile always uses exotic gas mixtures, and a tekkie BCD has at least six D-rings attached! A tekkie dive maximizes complexity and difficulty! A tekkie aspires to be the most authoritative expert ... on everything!

telltale :
any of various devices or mechanisms for alerting, indicating, or registering, including a suspended line, ribbon, or feather hung so as to indicate wind direction.

tempest :
a violent windstorm with rain.

tender :
an auxiliary watercraft, such as a dinghy or motorboat, that's carried or towed by a larger vessel so as to "attend" to its needs; as derived from 'attender'.

tender garage :
a hollow interior within the hull of a ship or within the chamber of a moored platform, that admits surface or subsurface vessels through a water-tight or pressure-resistant opening (shell door) for staging, docking, and other tasks associated with auxiliary vessels.

tension leg rig :
a permanently moored floating platform that's used for offshore excavation and development, the structure of which is tethered in deep water (300-1500m), rendering the rig impervious to vertical movement.

test depth :
the rated maximum safe depth to which a submarine or other submersible is tested by actual or simulated submergence, as based upon design and manufacturing limits.

thermocline :
an underwater layer of boundary water that differs in temperature and salinity from those bordering it above and below; it is the region in a thermally stratified body of water which separates warmer oxygen-rich surface water from cold oxygen-poor deep water and in which temperature decreases rapidly with depth. Also, a layer in a large body of water, such as a lake, that sharply separates regions differing in temperature, so that the temperature gradient across the layer is abrupt. Also, the intermediate summer or transition zone in lakes that's situated between the overlying epilimnion and the underlying hypolimnion, defined as that middle region of a thermally stratified lake or reservoir in which there is a rapid decrease in temperature with water depth. Typically, the temperature decrease reaches 1°C or more for each meter of descent (equivalent to 0.55°F per foot).

thirds :
the practice of dividing the volume of air (in cubic feet or psi) into thirds: with one third for the penetration, one third for the exit, and one third for emergency use; also called the "rule of thirds".

thorax :
the part of the mammalian trunk between the neck and the abdomen, containing the heart and lungs in a bony cage of ribs, sternum, and vertebrae, and separated from the lower trunk by the diaphragm; also known as the chest.

throughflow :
the horizontal movement of water beneath the saturated land surface once it has infiltrated the less permeable compacted soil, moving downwards and sideways under gravity and running underground until it reaches a river, lake, or other body of water. Also, the transport of ocean water in a horizontal current from one body to another by way of a channel (such as the Indonesian throughflow) as an adjustment in sea levels, with or without the augmented movement of seasonal winds; also known as an "oceanic conveyor belt".

throw line :
a light cord or thin rope, with its trailing end weighted by a knot, that's used to cast across an intervening space or to toss between footholds for transferring larger cables; also known as a "messenger line" or "heaving line".

thumbing the dive :
a command signal used to terminate the dive and direct other divers to exit to the surface; this "thumbs-up" hand signal consists of an upward pointing thumb with the fingers of that same hand closed into a fist.

thumbs-up :
a hand signal indicating ascent; not to be mistaken for a gesture of approval or agreement.

thwart :
passing or lying crosswise or across; transverse or athwart. Also, a transverse member spreading the gunwales of a small boat, canoe, or the like. Also, a seat across a boat, as one used by a rower.

tidal range :
the difference in height between the highest (hwl) and lowest (lwl) water levels occurring about every 12-hours.

tidal wave :
common reference to a large, destructive ocean wave that was produced by a seaquake, hurricane, or other cataclysm. Also, either of the two great wavelike swellings of the ocean surface that move around the earth on opposite sides and give rise to tides, as caused by the attraction of the moon and sun.

tide :
the periodic rise and fall of the waters of the ocean and its inlets, produced by the attraction of the moon and sun, and occurring about every 12-hours. Also, the inflow, outflow, or current of water at any given place resulting from the waves of tides. Also, a flood tide, being the inflow of rising water. Also, betide; to happen or befall.

tide gate :
a gate that permits water to flow through when the tide moves in one direction, but closes automatically when the tide moves in the opposite direction. Also, a restricted passage through which the tide flows swiftly, such as a strait. [cf: water gate]

tidehead :
the inland limit of the tide.

tiller :
a bar or lever fitted to the head of a rudder that's used for turning the rudder when steering.

timberhead :
the top end of a timber, rising above the deck and serving for belaying ropes or attaching lines. Also, a bollard resembling this in position and use.

time to fly :
the surface interval (SI) that must elapse after underwater diving so as to reduce tissue gas concentrations to a level where the risk of decompression sickness is acceptable, due to the pressure reduction experienced in normal commercial airliners.

toe rail :
the raised lip at the edge of a weather deck that's designed to prevent someone's feet from slipping or sliding overboard.

tongue :
a narrow strip of land extending into a body of water; cape. Also, a section of ice projecting outward from the submerged part of an iceberg.

topside :
on deck, or on the outer-surface of the hull above the waterline, often refers only to the main deck; also known as "topsides".

tornado :
the word 'tornado' is a metathetic variant of "tronada", a violent thunderstorm, which is characterized as a violent funnel-shaped windstorm occurring over localized land.

torr :
a unit of pressure, being the pressure necessary to support a column of mercury one millimeter high at 0°C at standard gravity, and equal to 1333.2 microbars; eponymously after Evangelista Torricelli, an Italian physicist.

Torricelli's law :
the law that states that the speed of flow of a liquid from an orifice is equal to the speed that it would attain if falling freely a distance equal to the height of the free surface of the liquid above the orifice; named after Evangelista Torricelli, an Italian physicist.

total bottom time :
the amount of time that a diver spends underwater, being the sum of actual bottom time and residual nitrogen time.

touch signal :
contact communications used in a low visibility environment; including: Go (by a push), Stop (by a pull), Back Up (by several rapid pulls), Turn (by taps on side to move), Exit (by taps on head).

tourist :
see holiday diver, recreational diver.

towhead :
a sand bar in a river, especially a sand bar with a stand of cottonwood trees.

trachea :
the tube that extends from the larynx to the bronchi, which serves as the principal passageway for air to and from the lungs; this airway is also called the windpipe.

trailing edge :
the rear edge of a moving object, especially a propeller blade or airfoil. [v: chord] Also, the rear edge of a mass of air or water.

trailing line :
a recovery line suspended in the water from a moving craft or vessel; also called trawl or trawl line. Also, a safety line that's temporarily laid to mark the route and establish boundaries; a rope or cord emplaced to direct someone's passage over unfamiliar or confusing terrain; also called guideline, distance line, lay line, cave line, or penetration line. Also, in naval navigation, the mechanism by which a log or patent log is streamed from a vessel; also called log line.

tramp :
a freight vessel that transports cargo wherever the shippers direct, having no regular schedule and no fixed port or route; also called "tramp steamer" or "tramp ship".

transition layer :
the stratified layer of a body of water that's situated between the mixed layer and the undisturbed fluid beneath it; being the uppermost (epilimnion) thermocline or the thermocline closest to the surface at any given time. Also, the capping inversion or entrainment zone at the top of the convective mixed layer. Also, the statically stable layer near the base of convective clouds in the Tropics. Also, the thin layer that separates thicker layers of different characteristics.

transom :
a flat termination at the stern of a ship above the water line; or any of the transverse beams attached to the sternpost of a ship that strengthen the stern.

travel gas :
the breathing mixture used for descent and ascent.

trawl :
a recovery line trailing from a moving craft or vessel, which enables divers or swimmers to be extracted from a body of water by attaching themselves onto the line while the craft or vessel continues, without stopping to embark the departing personnel, who are later transferred to their host ship; this term derives from "trail", and is also called "trawl line" or "dragrope". [nb: fishermen use a "trawl net"]

tread :
to maintain the body in an erect posture or upright position in the water, with the head above the surface, as performed by a pumping or cycling movement of the legs, similar to a stepping or walking motion, with the arms used for balance and stability; also called "duck paddling". Also, used figuratively to represent the maintenance of the status quo, without making any progress; being static or dormant, fixed or unchanging.

trench :
a long narrow depression in the deep-sea floor, being the site of one or more ocean deeps.

trident :
a three-pronged spear-like device or weapon that's characteristically associated with Poseidon or Neptune; as derived from "having three teeth".

trigger snap :
a hardware device used to attach gear to the diver's harness; it has a swivel on one side and a split circular other end with one side of the split being a spring-loaded lever (trigger).

trim :
the set of a ship in the water, especially the most advantageous posture with respect to the intended course and the prevailing conditions; also called attitude adjustment. Also, to adjust the sheets of a sailing vessel so that it floats on an even keel; level at the waterline. Also, the most advantageous posture or the balanced set of any body in the water, especially a swimmer or diver.

trimix :
a breathing gas mixture of nitrogen, helium, and oxygen.

trim party :
the directed movement of passengers or crew aboard ship so as to alter the trim of that vessel; originally used aboard submarines to increase the rate of ascent or descent; this practice is sometimes used to harass inexperienced helmsmen. [cf: body English]

trim weight :
weights attached to the diver that allow adjustment for trim and swimming position. Also, weight (eg: ballast, cargo, etc) aboard ship that can be positioned or shifted so as to effect the proper balance or the greatest stability.

Tropic of Cancer :
a parallel of latitude that marks the farthest point (23.5°N) north of the equator where the sun's rays fall vertically.

Tropic of Capricorn :
a parallel of latitude that marks the farthest point (23.5°S) south of the equator where the sun's rays fall vertically.

truck :
a circular piece of wood fixed on the head of a mast or the top of a flagstaff, usually containing small holes for the roving through of signal halyards. Also, any of various wheeled frames used for transporting large or heavy objects, including packages and cartons, trunks and crates; also called dolly or hand truck. Also, miscellaneous articles of little worth; odds and ends.

tsunami :
an unusually large sea wave produced by a seaquake or undersea volcanic eruption; originating in Japanese as "harbor wave".

turbidimeter :
a device for measuring the turbidity or opacity of water or any other liquids.

turbulence / turbulent :
being in a state of agitation or disorder; manifesting a violent commotion or tempestuous disturbance, such as exhibited by the haphazard secondary motion caused by eddies within a moving fluid, or by irregular motion of the atmosphere, as that indicated by gusts and lulls in the wind; term derives from 'restless'. [v: tumult / tumultuous]

turbulent flow :
the flow of a fluid past an object such that the velocity at any fixed point in the fluid is inconstant, changeable, or varies in an irregular or unpredictable manner; the variable path of suspended particles that are moving erratically or eccentrically in a fluid medium past an object. [cf: streamline flow; v: hydrodynamics, fluid dynamics]

Turk's Head :
a large decorative knot, used to finish a special line or lanyard (such as one suspended from the clapper of a ship's bell); sometimes called "Nigger Head" or "niggerhead".

turn :
to pass or twist a rope entirely around an object; as derived from "round off" or "make circles". Also, a single circular or convoluted shape, as of a coiled or wound rope.

turn the tide :
an expression of figurative reversal, as to reverse the course of events, especially from one extreme to another; as derived from the literal reversal of flow.

'tween deck :
any space between two continuous decks in the hull of a vessel, as between a shelter deck and a freeboard deck.

Type III MSD :
the Type III Marine Sanitation Device, a sewage retention system or holding tank (qv).

typhoon :
a tropical cyclone or hurricane of the western Pacific, its seas and inland areas; as derived from Chinese for great wind. [cf: Greek Typhoeus / Typhon]

undercurrent :
a water current that flows below the upper currents or beneath the surface.

undertow :
any strong subsurface current that's moving in a direction different from that of the surface current, especially the seaward flow of subsurface water from waves breaking on a beach.

underway / under way :
a moving vessel, as a boat or ship that's no longer at anchor or in port; a vessel that's not stationary, is in motion relative to the seafloor, but may not be under its own propulsive power.

upper deck :
the uppermost continuous deck that is capable of being made watertight; also called freeboard deck.

upstream valve :
a valve that functions against the flow of pressure (instead of with the flow of pressure), such that if it fails, this valve is safely closed in the 'off' position.

Valsalva maneuver :
an attempt to adjust pressure in the middle ear by forcibly expelling air against a closed glottis, or against closed lips and pinched nostrils, which inflates the Eustachian tubes while decreasing intrathoracic pressure, hampering venous return to the heart; eponymously after Antonio M. Valsalva, an Italian anatomist.

vampire gauge :
slang for a penetration monitor that samples blood gas (abg) diffusion at the wrist, which is used on deep underwater dives.

van der Waals equation :
the Johannes van der Waals formula is a gas law involving the pressure, temperature, and volume of real gas variations, instead of ideal gas at absolute temperature, and is given as: (P + a/v2) (v - b) = RT, or (pressure + constant value a squared)(volume minus constant value b) = (real gas temperature).

veer :
said of the wind when it changes. Also, to slacken a cable and let it run out [v: pay].

veer and haul :
to alternately pull on and slacken a rope or line, as in warping, until the vessel gains headway.

venous gas embolism :
a condition in which gas bubbles enter the venous system and cause damage by blocking blood flow to vital organs, most commonly the heart and lungs; abbreviated VGE, and also called "air embolism".

vertigo :
a dizziness or disordered condition brought on by the inequality of pressures in the inner ear; a sign of ear barotrauma that may range from minor ear squeeze to perforation of the eardrum.

abbreviation for Venous Gas Embolism.

abbreviation for Visual Inspection Program, being the visual inspection of the interior (and exterior) of a scuba cylinder to warrant its integrity, as performed annually by a trained equipment technician.

visibility :
the viewing distance or visual capacity for underwater objects as factored by bottom composition, turbidity, suspended matter, and water temperature.

visual reversal :
a perceptual distortion where the distance to an underwater object appears farther away than the actual distance.

volute :
an object having a spiral, twisted, or rolled-up conformation, especially the turn or whorl of a spiral seashell. Also, the scrolled ornament terminating a handrail or cutwater.

vortex :
a whirling mass of water, especially one operating with the force of suction, as a whirlpool.

V-weight :
a weight placed between a set of air cylinders to offset an undesired buoyancy or to adjust a diver's trim.

wake :
the track of waves left by a vessel moving through water; as derived from a "hole in the ice". Figuratively, as "in the wake of", means consequently or closely behind.

wale :
any of certain strakes of thick outside planking on the sides of a wooden ship.

waler :
a structural member that's fastened along the edges of a dock system to hold it together, to provide stability, and to protect the flotation pontoons and utility feeds.

Wallacea :
a biogeographical transition zone of islands between the Sunda shelf and the Sahul shelf, an area separating Australia from Southeast Asia for the past seventy million years. Initially recognized for its significance by the British naturalist Alfred Russel Wallace, it marks the division between two major faunal groups: oriental animals (elephants, tigers, and apes) and Australasian animals (marsupials and monotremes). The so-called "Wallace Line", which runs between Bali and Lombok, is a boundary that separates the ecozones of Asia and Australasia, with the organisms living west of this line related to Asiatic species, and most of the species east of this line endemic to Australia, New Guinea, New Zealand, and neighboring islands. [v: Weber's Line, Huxley's Line, Lydekker's Line]

wall diving :
underwater exploration along the face of a vertical surface (cliff or quarry, pit or drop-off), which requires good buoyancy control to avoid angling upward to the surface or downward to the seafloor.

warp :
a rope smaller than a cable and used as mooring lines. Also, to move a vessel from one place to another by means of incremental hauling on a rope made fast to some fixed object, or to a kedge (kedging).

washing machine / washer machine :
slang for the churning turbulence generated by a whirlpool, plunge pool, riptide, undertow, or waterspout, which can be disorienting and potentially dangerous to swimmers and divers.

watch :
a lookout, guard, sentinel, or selected crewmembers who serve as such while aboard a vessel. Also, a period of time during which part of the crew is on duty attending to the workings of their ship. Also, one of the periods (usually four hour blocks) into which the day and/or night is subdivided while at sea.

watch-and-watch :
the necessity to stand alternate watches, due to an absence or incapacity of other crewmembers; variously arranged as 4- or 6-hours on- and off-duty until the situation changes; this routine is also called "port and starboard" or "port and stupid" ... an exhausting schedule that can inadvertently generate mistakes and accidents.

watch bill :
a roster of regularly scheduled duties assigned to crewmembers.

watch cap :
a soft stocking-cap, knitted of dark blue wool and worn with a turned-up cuff folded at the bottom, that's suitable for wear during cold weather by seamen or sailors. [cf: balaclava, coif, pileus/pîlos]

watercourse :
any natural channel conveying water, seasonally or otherwise, as a river or stream; a waterway. Also, a conduit or canal made for the conveyance of water, as a race or aqueduct.

watercraft :
any type of boat, ship, or seagoing vessel; a waterborne conveyance. Also, skill in boating, or ability in watersports and related recreations.

waterfall :
a steep fall or flow of water in a watercourse from a rocky height, as over a precipice; a cascade or cataract.

waterfront :
land on the edge of a body of water. Also, the part of a city or town on the land beside a body of water.

waterhead :
the source of a river or stream; a fountainhead. Also, a body of water that's been impounded as a reservoir for irrigation or other utility.

water hole :
a depression in the surface of the ground that contains water, as a pond or pool, including a cavity in the dry bed of a river that contains water. Also, a hole in the frozen surface of a lake, pond, stream, or the like. Also, a source of drinking water, as a spring or well. [cf: watering hole]

waterline / water-line / water line :
the line in which water at its surface borders upon a floating body; being just the part of the outside of a ship's hull that's at the level of the water. Also, any of a series of lines on the shipwright's architectural hull plans of a vessel that represent the level to which the vessel is immersed or the bottom of the keel. Also, a tube, pipe, or hose for conveying liquids.

waterlocked :
enclosed entirely, or almost entirely, by water. Also, living in water cut off or shut away from the sea. [cf: landlocked]

waterlog :
to cause a boat, ship, or other vessel to become uncontrollable as a result of flooding. Also, to soak, fill, or saturate with water so as to make soggy or useless; apparently derived as a back-formation of waterlogged.

waterlogged :
excessively saturated with, or as if with, water; so filled or flooded with water as to be heavy or unmanageable.

watermanship :
skill in rowing or boating.

water plane :
the horizontal area of a ship when measured at the waterline.

water pocket :
a cavity at the foot of a cliff formed by the falling action of an intermittent stream; also known as a 'plunge basin' (qv).

watershed :
the area or region drained by a stream, river, or other watercourse. Also, an important point of division or transition.

watersport :
an activity played within or on the surface of water, or a recreation practiced within or on the water's surface.

waterspout :
a funnel-shaped or tubular portion of a cloud that's so laden with mist and spray that it resembles a solid column of water connecting the ocean, or other body of water, to the sky; a tornado at sea.

waterway :
any natural channel conveying water, seasonally or otherwise, as a river or stream; a watercourse.

waveson :
goods that appear upon the waves or floating at sea after a shipwreck.

way :
movement or passage through water, as being underway or making headway. Also, a ramp, usually two or more, along which the hull of a boat slides when being launched.

weather deck :
the uppermost continuous deck on a ship that's without overhead cover, and so is fully exposed to the weather.

weight belt :
a buckled belt worn around a diver's waist which holds enough weights to offset the diver's buoyancy.

weight system / weighting system :
the addition or subtraction of weights to a diver's gear so as to offset the diver's buoyancy as calculated for a particular dive profile; the use of weights as buoyancy compensators.

well :
a natural or artificial hole, as a depression or reservoir, for the containment of water, or to supply a spring or fountain. Also, a part of a weather deck between two superstructures, extending from one side of a vessel to the other.

well deck :
a space on the weather deck of some ships that lies at a lower level, between a raised forecastle or poop and the superstructure of the bridge, which can be flooded to embark and disembark boats, landing craft, or amphibious tractors.

wet suit / wetsuit :
a close-fitting rubber or neoprene garment that's worn by a skin or scuba diver in cold water, that allows a thin insulating layer of water to collect between the diver's body and the suit, in order to retain body heat; invented in 1952 by Hugh Bradner, a physicist at the University of California in Berkeley.

whaleboat :
a long, narrow, open boat designed for quick turning and use in rough seas; also known as a whaler or Boston whaler, it was formerly used in whaling, but now mainly for sea rescue.

wharf :
a structure built on the shore of a harbor or estuary, or projecting into such a body of water, for the mooring of vessels and the transfer of passengers or cargo.

whimsy / whimsey :
an odd or capricious windstorm that creates turbulent water.

whip :
to overlay or cover cordage or rope with thread or line, as for prevention of damage by friction, fraying, or raveling [cf: puddening, mousing, baggywrinkle]. Also, a tackle consisting of a fall rove through a single standing block (single whip), or a fall secured at one end and rove through a single running and a single standing block (double whip). Also, the hose used for filling compressed air tanks.

whipping :
the binding on the end of a line or wire to prevent unraveling.

whirlpool :
a swift circular motion of water, caused by the meeting of opposing currents, often producing a downward spiral.

whitecap :
a broken wave with a foaming crest; also called "white horses" for their dancing movement.

white squall :
a strong sudden gust of wind that arises without warning, exhibited by broken water or whitecaps; usually seen in whirlwind form during clear weather in the tropics.

white water :
frothy water, as in whitecaps and rapids. Also, light-colored sea water over a shoal or sandy bottom.

white-water rafting / whitewater rafting :
to quickly float downstream through frothy rapids and churning falls on a buoyant raft or in an inflated inner-tube, in a lightweight boat (canoe or kayak) using paddles, or in a small dinghy using body English for steering; after moving over or through rapids, conveyances may be beached along the route for recuperation, nature study, or over-night encampment.

whole gale :
a wind of 55-63mph, as measured on the Saffir-Simpson scale.

wildcat :
that portion of a windlass that engages the links of the anchor chain so that it can be heaved in. [cf: pawl, dog]

winch :
a machine having a drum on which to coil a rope, cable, or chain used for hauling, pulling, or hoisting; sometimes called a "windlass".

winding :
the act or process of turning a vessel end for end between buoys, or along-side a wharf or pier.

winding hole :
the place in a canal or channel where long and/or narrow boats are able to turn around; also known as "winded".

windlass :
a mechanical device used to pull in cable or chain, such as an anchor rode; a capstan or winch.

windless :
a cranked handle used for mechanical winding. [cf: capstan-bar, handspike]

wind sail :
a sail rigged over a hatchway, ventilator, or the like, that's used to divert moving air downward into the vessel.

windsock :
a tapered tubular cloth vane ("weather vane") or TELLTALE, that pivots to catch the wind, swinging freely so as to indicate the direction toward which the wind is blowing.

windward :
in the direction of the prevailing wind; toward the point or quarter from which the wind blows.

wings :
informal term for inflatable bladders (air cells) that ride on either side (surrounding) of back-mounted tanks, and have a specified lift capacity, generally from 35 to 100 pounds; a back-mounted buoyancy compensator.

within limits :
representation of a dive profile that conforms to the table limits specified for the safe conditions of a dive.

woe betide :
distress comes, suffering comes to pass, trouble happens, grief is visited upon, befallen by sorrow; not bêtise or betied. [cf: woebegone (beset with woe)]

Woods Hole Oceanographic Institution :
a research facility, established 1930 and situated at a seaport in Falmouth, at the southwestern extremity of Cape Cod, which uses several ocean-going vessels and marine laboratories to study oceanography, biology, meteorology, geology, and geophysics; Woods Hole is also the site of the U.S. Marine Biological Laboratory, and the U.S. Bureau of Commercial Fisheries Biological Laboratory and Aquarium.

wrap :
technique for attaching guideline to a rock, especially at the secondary tie-off.

wreck diving :
underwater exploration of shipwrecks and other sunken vessels, especially for salvage or historical research.

yardarm :
either end of a center-mounted spar or yard; also called stick. In modern vessels, the place where flags and pennants are often attached.

yaw :
the rotation of a ship about its vertical axis so as to cause its longitudinal axis to deviate from the heading in its horizontal plane; the deviating motion or axial oscillation of a vessel from its straight course or stable attitude.

Y-valve :
an air tank valve with two outlets; a dual outlet valve shaped in the form of the letter 'Y' that's used with single cylinders; also called a slingshot valve.

zip tie :
ratcheted plastic strip that is used to securely attach accessory items to a bolt clip; used in lieu of tied line.

Z-knife :
a line-cutter consisting of a handle and blade guard with a razor blade inside a slot.

Zodiac :
brand name of an inflatable squad-sized assault boat with a stern plate for the optional mounting of an outboard motor, wherein the equipment is stowed inside the craft while the troops sit on the inflated sides to direct it; designed by aquanaut Jacques Y. Cousteau. [v: Avon, Parker, Brunswick]

Zytel :
brand name for a number of different formulations of high strength, abrasion and impact resistant nylon engineered by DuPont with varying proportions of fiberglass (13%-60%) added for stiffness; some of these thermoplastic polyamide formulations (including polyphthalamide) are reinforced with glass, mineral, rubber, Kevlar, or Teflon in order to achieve specific characteristics.

underwater diver