marine glossary

Glossary of Marine Terms

The following table contains a list of Marine terms originally collated for the ecPilot Website. The glossary has been edited and added to by EDINA.

ecPilot Glossary
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Abnormal Magnetic Variation	Designation applied to any anomalous value of the magnetic variation of which the cause is unknown. See also local magnetic anomaly.
Aboard	In the sense used in pilotage and ship handling means "near". eg "To keep the E shore aboard". "Close aboard" means "Very near". See also borrow.
Above	Uptide or upstream of a position.
Above-Water	A shoal, rock or other feature is termed above-water if it is visible at any state of the tide. See also awash, dries, below-water.
Abrupt	Steep: precipitous. See also bold.
Abyssal Gap	A narrow break, in a ridge or rise, or separating two abyssal plains.
Abyssal Hills	A tract of small elevations on the sea floor.
Abyssal or Abysmal	Relating to the greatest depths of the ocean (literally, without bottom).
Abyssal Plain	A flat, gently sloping or nearly level region at abyssal depths.
Accretion or Deposition	The depositing of material on the bottom or the coast by water movement; the opposite to erosion.
Advance	When altering course, the distance that the compass platform of a ship has advanced in the direction of the original course on completion of a turn (the steadying point). It is measured from the point where the wheel was put over.
Aeronautical Radiobeacon	A radiobeacon primarily for the use of aircraft. Usually abbreviated to "aero radiobeacon".
Affluent	A tributary river or brook.
Afloat	Floating, as opposed to being aground.
Age of the Moon	The interval in days and decimals of a day since the last New Moon.
Age of the Tide	Old term for the lag between the time of new or full Moon and the time of maximum spring tidal range.
Agonic Line	A line joining points on the Earth's surface where there is no magnetic variation.
Aground	Resting on the bottom.
Alongside	A ship is alongside when side by side with a wharf, wall, jetty, or another ship.
Amphidrome	A point in the sea where the tide has no amplitude. Co-tidal lines radiate from an amphidromic point and co-range lines encircle it.
Anchor Bearing	The bearing of a shore object from the position of the anchor.
Anchor Buoy	Small buoy occasionally used to mark the position of the anchor when on the bottom; usually painted green (starboard) or red (port), and secured to the crown of the anchor by a buoy rope.
Anchorage	Water area which is suitable and of depth neither too deep nor too shallow, nor in a situation too exposed, for vessels to ride in safety. An area set apart for vessels to anchor.
Angle of Cut	The lesser angle between two position lines.
Aphelion	The point in the orbit of a planet which is farthest from the Sun. See also perihelion.
Apogee	The point in the orbit of the Moon which is farthest from the Earth. See also perigee.
Approaches	The waterways that give access or passage to harbours, channels, etc.
Apron	The portion of a wharf or quay lying between the waterside edge and the sheds, railway lines or road.
Arc of Visibility	The sector, or sectors, in which a light is visible from seaward.
Arch	Geologically, a covered passage cut through a small headland by wave action.
Archipelagic Apron	A gentle slope with a generally smooth surface on the sea floor, particularly found around groups of islands or seamounts.
Area To Be Avoided	A routing measure comprising an area within defined limits in which either navigation is particularly hazardous or it is exceptionally important to avoid casualties and which should be avoided by all ships, or certain classes of ship.
Arm (of a Jetty, Etc)	A narrow portion projecting from the main body.
Arm of the Sea	A comparatively narrow branch or offshoot from a body of the sea.
Arming the Lead	Placing tallow in the recess in the bottom of the sounding lead to ascertain the nature of the bottom.
Artificial Harbour	A harbour where the desired protection from wind and sea is obtained from moles, jetties, breakwaters, etc. (The breakwater may have been constructed by sinking concrete barges, vessels, etc, to form a temporary shelter.)
Artificial Horizon	A horizon produced by bubble, gyro or mercury trough to allow measurement of altitude of celestial bodies.
Astronomical Arguments	See Admiralty Tide Tables.
Astronomical Twilight	The period between the end of nautical twilight and the time when the Sun's centre is 18° below the horizon in the evening, and the period between the time when the Sun's centre is 18° below the horizon in the morning and the beginning of nautical twilight.
Atoll	A ring-shaped coral reef which has islands or islets on it, the shallow rim enclosing a deeper natural area or lagoon; often springing from oceanic depths.
Atollon	A small atoll on the margin of a larger one.
Automatic Tide Gauge	An instrument which measures and records the tidal data.
Average Rate	The rate to the nearest 1/4 kn of the highest 50% in predominant sectors as indicated by the figures on the current diagrams. It is emphasised that rates above or below those shown may be experienced.
Awash	A shoal, rock or other feature is termed awash when its highest part is within 0·1 m, or with fathoms charts within 1 foot, of chart datum.
Awash At High Water	May be just visible at MHWS or MHHW. See also dries, above-water.
Back	The wind is said to back when it changes direction anticlockwise.
Backshore	That part of the shore whose seaward limit is the waterline of MHWS and whose landward limit is the extreme limit of wave action (such as occurs in onshore gales at equinoctial spring tides).
Backwash	Waves reflected from obstructions such as cliffs, seawalls, breakwaters, etc, running seaward and combining with the incoming waves to cause a steep and confused sea.
Backwash Marks	Small scale oblique reticulate pattern sometimes produced by the return swash of the waves on a sandy beach. See also ripple marks, beach cusps.
Backwater	An arm of the sea, usually lying parallel with the coast behind a narrow strip of land, or an arm of a river out of the main channel, and out of the main tidal stream or current.
Bank	Oceanographically, an area of positive relief over which the depth of water is relatively shallow, but normally sufficient for safe surface navigation. The term should not be used for features rising from the deep ocean. Also, the margin of a watercourse, river, lake, canal, etc. The right bank of a river is the one on the right hand side when facing downstream.
Bar	A bank of sand, mud, gravel or shingle, etc near the mouth of a river or at the approach to a harbour, causing an obstruction to entry.
Bar Buoy	A buoy indicating the position of a bar.
Barrier	An obstruction, usually artificial, in a river. eg Thames Barrier.
Barrier Reef	A coral reef, lying roughly parallel with the shore, but separated from it by a channel or lagoon. the distance offshore may vary from a few metres to several miles.
Basalt	Dark green or brown igneous rock, often in columnar strata.
Basin	An almost land-locked area leading off an inlet, firth or sound. Also, an area of water limited in extent and nearly enclosed by structures alongside which vessels can lie. Oceanographically, a depression more or less equidimensional in form, and of variable extent.
Bathymetry	The science of the measurement of marine depths. Submarine relief.
Bay	A comparatively gradual indentation in the coastline, the seaward opening of which is usually wider than the penetration into the land. See also bight, gulf.
Bayou	Term used in Florida for a small bay, and in Mississippi and Louisiana for a waterway through lowlands or swamps, connecting other bodies of water, and usually tidal or with an imperceptible current.
Beach	Any part of the shore where mud, sand, shingle, pebbles, etc, accumulate in a more or less continuous sheet. the term is not used to describe areas of jagged reef, rocks or coral.
Beach Cusps	Triangular ridges, or accumulations, of sand or other detritus regularly spaced along the shore, the apex of the triangle pointing towards the water, giving a serrated form to the water-edge.
Beach Ridges	The seaward boundaries of successive positions of beaches on seaward-advancing shores. the intervening depressions may be extensive and contain a lagoon, marsh, mangrove swamp, etc, or be narrow and consist of sand. See also storm beach.
Beacon	A fixed artificial navigational mark, sometimes called a daybeacon in the USA and Canada. It can be recognised by means of its shape, colour, pattern or topmark. It may carry a light, radar reflector or other navigational aid.
Beacon Tower	A major masonry beacon the structure of which is as distinctive as the topmark.
Beam Sea	The condition where the sea and swell approach the ship at approximately 90° from the ship's head.
Bed	The bottom of the ocean, sea, lake or river. Usually qualified, eg seabed, river bed.
Bell-Buoy	A buoy fitted with a bell which may be actuated automatically or by wave motion.
Below-Water	A shoal, rock or other feature is termed below-water or underwater if it is not visible at any state of the tide. See also above-water.
Benchmark	A mark, which may consist of an arrow cut in masonry, a bolthead or a rivet fixed in concrete, etc, whose height, relative to some particular datum is exactly known. (See Admiralty Tidal Handbook No 2.)
Berm	An horizontal ledge on the side of an embankment or cutting to intercept falling earth or to add strength. Also, a narrow, nearly horizontal shelf or ledge above the foreshore built of material thrown up by storm waves. the seaward margin is the crest of the berm.
Berth	The space assigned to or taken up by a vessel when anchored or when lying alongside a wharf, jetty, etc.
Berthing Dolphins	Dolphins against which a ship may lie. Also known as breasting dolphins.
Bight	A crescent-shaped indentation in the coastline, usually of large extent and not more than a 90° sector of a circle. See also bay, gulf.
Bilge (or Keel) Blocks	A row of wooden blocks on which the bilges (or keel) of a ship rest when she is in dock or on a slipway.
Bill	A narrow promontory.
Blather	Very wet mud, a feature of estuaries and rivers; of a dangerous nature such that a weight will at once sink into it.
Blind Rollers	When a swell wave encounters shoal water it is slowed and becomes steeper. If the depth or extent of the shoal or rock is sufficient to cause the wave to steepen markedly but not to break, the resulting wave is termed a blind roller.
Bluff	A headland or short stretch of cliff with a broad perpendicular face. As adjective: Having a broad perpendicular or nearly perpendicular face.
Boat Harbour	An area of sheltered water in a harbour set aside for the use of boats, usually with moorings, buoys, etc.
Boat House	A shed at the water's edge or above a slipway for housing a boat or boats.
Boat Slip	A slipway designed specifically for boats.
Boat Yard	A boat-building establishment.
Bog	Wet spongy ground consisting of decaying vegetation, which retains stagnant water, too soft to bear the weight of any heavy body. An extreme case of swamp or morass.
Bold	Rising steeply from deep water. Well-marked. Clear cut. See also abrupt.
Bold-To	Synonymous with steep-to.
Bollard	A post (usually steel or reinforced concrete) firmly embedded in or secured on a wharf, jetty, etc, for mooring vessels by means of wires or ropes extending from the vessel and secured to the post. A very small bollard for the use of barges and harbour craft may be called a 'dollie'.
Boom	A floating barrier of timber used to protect a river or harbour mouth or to enclose a boat harbour or timber pound. Also, a barrier of hawsers and nets supported by buoys used in the defence of a port or anchorage.
Booming Ground	A term used mainly in Canadian waters, and similar to timber pound where logs are temporarily held and stored for making up into rafts. the area is usually enclosed by a boom to retain the logs.
Bore	A tidal wave which propagates as a solitary wave with a steep leading edge up certain rivers. Formation is most apparent in wedge-shaped shoaling estuaries at times of spring tides. See Admiralty Manual of Tides.
Borrow	In the sense used in pilotage means "keep towards, but not too near", eg "To borrow on the E side of the channel". See also aboard.
Boulders	Water-rounded stones more than 256 mm in size, ie larger than a man's head, See also cobbles.
Brackish	Water in which salinity values range from approximately 0.50 to 17.00.
Breakers	Waves or swell which have become so steep, either on reaching shoal water or on encountering a contrary current or by the action of wind, that the crest falls over and breaks into foam.
Breaking Sea	The partial collapse of the crests of waves, less complete than in the case of breakers, but from the same cause; also known as White Horses.
Breakwater	A solid structure, such as a wall or mole, to break the force of the waves, sometimes detached from the shore, protecting a harbour or anchorage. Vessels usually cannot lie alongside a breakwater.
Bridge	A narrow ridge of rock, sand or shingle, across the bottom of a channel so as to constitute a shoal or shallow. Structure carrying road etc across waterway, road ravine etc. Movable bridges are usually swing bridges, or lifting or bascule bridges. Swing bridges may pivot about a point, either in mid-channel or on one bank. Bascule bridges may be a single or double, depending on whether they lift from one or both banks.
Bridge-Islet	An island which is connected to the mainland, or to a larger island, at low water, or at certain states of the tide, by a narrow ridge of rock, sand, shingle, etc.
Broach To	To slew around inadvertently broadside on to the sea, when running before it.
Broadside On	Beam on (eg to wind or sea).
Broken Water	A general term for a turbulent and breaking sea in contrast to comparatively smooth and unbroken water in the vicinity.
Brook	A small stream.
Brow	An arrangement of wooden planking to give passage between ship and shore when the ship is alongside. Also called a "gangway".
Building Slip	A space in a shipbuilding yard where foundations for launching ways and keel blocks exist and which is occupied by a ship when being built.
Buoy	A floating, and moored, artificial navigation mark. It can be recognised by means of its shape, colour, pattern, topmark or light character, or a combination of these. It may carry various additional aids to navigation. See also lanby, light-buoy.
Buoyant Beacon	A floating mark coupled to a sinker either directly or by a cable that is held in tension by the buoyancy of the mark. Its appearance above the water generally resembles a beacon rather than a buoy; it does not rise and fall with the tide; and it normally remains in a vertical or near-vertical position. Formerly known as a Pivoted Beacon.
Cable	A nautical unit of measurement, being one tenth of a sea mile. Also, a term often used to refer to the chain cable by which a vessel is secured to her anchor. Also used to refer to submarine, or overhead, power or telephone cables.
Cable Buoy	A buoy marking the end of a submarine cable on which a cable ship is working. Also used in the sense of a telegraph buoy.
Cairn	A mound of rough stones or concrete of pyramidal or beehive shape used as a landmark.
Caisson	A structure used to close the entrance to dry docks, locks and non-tidal basins. They are of two kinds; floating caissons which are detachable from the entrance they close, and sliding caissons which slid into a recess at the side of the dock. See also cofferdam.
Calcareous	Formed of, or containing, carbonate of lime or limestone.
Calving	The breaking away of rock, stones, earth, etc from the face of a cliff.
Camber	A small basin usually with a narrow entrance, generally situated inside a harbour. eg Boat camber: a small basin for the exclusive use of boats.
Camel	A tank filled with water and placed against the hull of a stranded or sunken vessel. It is well secured to the vessel and then pumped out, the buoyancy thus added helping to lift the vessel.
Can Buoy	A nearly cylindrical buoy moored so that a flat end is uppermost.
Canal	A channel dredged or cut through dry land or through drying shoals or banks and used as a waterway. See also ship canal.
Canal Port	A port so situated that the waterway is entirely artificial.
Canyon	A deep gorge or ravine with steep sides, at the bottom of which a river flows. Oceanographically, a relatively narrow, deep depression with steep sides, the bottom of which slopes continuously downwards.
Cape	A piece of land, or point, facing the open sea and projecting into it beyond the adjacent coast.
Cargo Crane	For transferring cargo between a ship's hold and the shore or lighter.
Cast	To turn a ship to a desired direction without gaining headway or sternway.
Catamaran	A floating stage or raft used in shipyards, for working from, and sometimes used as a fender between ship and wharf, etc. Also, a type of twin-hulled yacht. (The name is taken from various native-built craft common in the East Indies and some other parts of the world).
Catwalk	A narrow footway forming a bridge, eg connecting a mooring dolphin to a pierhead. Also known as a walkway.
Causeway	A raised roadway of solid structure built across low or wet ground or across a stretch of water.
Cay	A small insular feature usually with scant vegetation; usually of sand or coral. Often applied to smaller coral shoals. See also islet.
Centreline Controlling Depth	A depth which applies only to the channel centreline: lesser depths may exist in the remainder of the channel.
Channel	A comparatively deep waterway, natural or dredged, through a river, harbour, strait, etc, or a navigable route through shoals, which affords the best and safest passage for vessels or boats. The name given to certain wide straits or arms of the sea, e.g. English Channel, Bristol Channel. Oceanographically, a river valley-like elongated depression in ocean basins, commonly found in fans.
Character or Characteristic of a Light	The distinctive rhythm and colour, or colours, of a light signal that provide the identification or message, see Admiralty List of Lights.
Chart Datum	A level so low that the tide will not frequently fall below it. in the United Kingdom, this level is normally approximately the level of Lowest Astronomical Tide. It is the level below which soundings are given on Admiralty charts, and above which are given the drying heights of features which are periodically covered and uncovered by the tide. Chart datum is also the level to which tidal levels and predictions are reffered in Admiralty Tide Tables.
Check Bearing	The bearing of an extra object taken to check the accuracy of a fix.
Cinders	Fragments formed when magma is blown into the air; larger in size than volcanic ash.
Circular Radiobeacon	A radiobeacon which transmits the same signal in all directions.
Civil Twilight	The periods of the day between the time when the Sun's centre is 6° below the horizon and Sunrise (morning twilight), or between sunset and the time when the Sun's centre is 6° below the horizon (evening twilight).
Claw Off	To beat or reach to windward away from a lee shore.
Clay	A stiff tenacious sediment having a preponderance of grains with diameters of less than 0·004 mm. It is impossible to differentiate between clay and silt by eye, but a sample of wet clay, when dried in the palm of the hand, will not rub off when the hands are rubbed together.
Clean	Applied to the bottom of the sea, harbour or river, means free from rocks or obstructions. See also foul.
Clearing Bearing	The bearing of an object, usually taken from a chart, to indicate whether a ship is clear of danger.
Clearing Marks	Selected marks, natural or otherwise, which in transit clear a danger or which mark the boundary between safe and dangerous areas for navigation.
Cliff	Land projecting nearly vertically from the water or from surrounding land, and varying from an inconspicuous slope at the margin of a low coastal plain to a high vertical feature at the seaward edge of high ground. Can be formed by a fault in geological strata (inland).
Close (Verb)	To approach near.
Close Aboard	Very near.
Coast	The meeting of the land and sea considered as the boundary of the land. See also shore. Also, the narrow strip immediately landward of the waterline of MHWS, or sometimes a much broader zone extending some distance inland.
Coast Radio Stations	Coast radio stations are normally open for public correspondence through which ships can pass messages for onward transmission. These stations are usually connected to the national telephone system. See the relevant Admiralty List of Radio Signals.
Coastal Plain	A strip of flat consolidated land varying in width which may occur immediately landward of the coastline.
Coastal Waters	The sea in the vicinity of the coast (within which the coasting trade is carried out).
Coasting	Navigating from headland to headland in sight of land, or sufficiently often in sight of land to fix the position of the ship by land features.
Coastland	The strip of land with a somewhat indeterminate inner limit, immediately landward of the coastline. It may include such features as sand dunes, saltings, etc, which are associated with proximity to the sea, and merges into the hinterland where the features cease.
Coastline	The landward limit of the beach. the extreme limit of direct wave action (such as occurs in onshore gales during Equinoctial Spring Tides. See also backshore. It may be some distance above the waterline of Mean High Water Springs, but for practical hydrographic purposes the two are usually regarded as coincident. Also, a general term used in describing the shore or coast as viewed from seaward, e.g a low coastline.
Coastwise (Adjective and Adverb)	Near to the coast, eg Coastwise traffic is that which sails round the coast, and to sail coastwise means coasting as opposed to keeping out to sea.
Cobbles	Water-rounded stones of from 64 mm to 256 mm in size, ie from the diameter of a man's clenched fist when viewed sideways to slightly larger than the size of a man's head. See also pebbles, boulders.
Cocked Hat	The triangle sometimes formed by the intersection of three lines of bearing on the chart. See also cut.
Cofferdam	Watertight screen on enclosure used in laying foundations underwater; sometimes called a caisson.
Collapsible Container	Can be stowed when not in use.
Combers	Steep, long swell waves with high breaking crests.
Conformal Projection	Another name for orthomorphic projection.
Confused Sea	The disorderly sea in a race; also when waves from different directions meet, due normally to a sudden shift in the direction of the wind.
Conical Buoy	A cone-shaped buoy moored to float point up. See also can buoy, nun buoy.
Conspicuous Object	A natural or artificial mark which is outstanding, easily identifiable, and clearly visible to the mariner over a large area of sea in varying conditions of light. If the scale is large enough they will normally be shown on charts in bold capitals, or on older charts by the note "conspic". See also Prominent.
Constancy	The thickness of the arrows (used on current diagrams) is a measure of its persistence; eg low constancy implies marked variability in rate and particularly direction.
Constants (Harmonic)	The phase-lag (g) and the amplitude (H) of a constituent of the tide.
Constants (Non-Harmonic)	The average time and height difference of high and low water, referred to the times and heights at a standard port; the time can also be referred to the time of Moon's transit.
Constituent (of the Tide)	The tidal curve can be considered as being composed of a number of cosine curves, having different speeds, phase-lags and amplitudes, the speed being determined from astronomical theory and the phase-lags and amplitudes being determined from observation and analysis. These cosine curves are known as constituents of the tide.
Container	A rigid, non-disposable, cargo-carrying unit, with or without wheels. Standard lengths are: 6·1 m (Twenty-foot Equivalent Unit (teu)) and 12·2 m (Forty-foot Equivalent Unit (feu)): both width and height are standardised at 2·44 m.
Container Crane	Specifically intended for handling containers.
Container Terminal	A specially equipped berth with storage area, where standard cargo containers are loaded or unloaded.
Continental Borderland	A province adjacent to a continent, normally occupied by or bordering a continental shelf, that is highly irregular, with depths well in excess of those typical of a continental shelf.
Continental Margin	The zone, generally consisting of the shelf, slope and rise, separating the continent from the deep sea bottom.
Continental Rise	A gentle slope rising from the oceanic depths towards the foot of the continental slope.
Continental Shelf	A zone adjacent to a continent (or around an island) and extending from the low water line to a depth at which there is usually a marked increase of slope towards oceanic depths. Conventionally, its edge is taken as 200 m, but it may be between about 100 m and 350 m.
Continental Slope	The slope seaward from the shelf edge to the beginning of a continental rise or the point where there is a general reduction in slope.
Contour	A line joining points of the same height above or depths below, the datum. See also fathom line.
Controlling Depth	The least depth within the limits of a channel: it restricts the safe use of the channel to draughts of less than that depth.
Convergence	The boundary or region where two converging currents meets, with the result that the water of the current of higher density sinks below the surface and spreads out at a depth which depends on its density.
Conveyor	Belt of buckets or similar contrivance for transporting cargo, especially ores or coal, from ship to shore or vice versa.
Coping	The top course of masonry in a wall: the waterside top edge of a wall.
Coral	Hard calcareous substance secreted by many species of marine polyps for support, habitation, etc. It may be found either dead or alive.
Coral Island	An island principally or entirely formed of coral. It may be one of three kinds: an elevated coral reef forming an island; a reef island formed by the accumulation of coral debris on a submerged fringing or barrier reef; or an atoll.
Coral Reef	Reefs, often of large extent, composed chiefly of coral and its derivatives. See also atoll, barrier reef, fringing reef.
Co-Range Lines	Lines on a tidal chart joining points which have the same tidal range or amplitude; also called co-amplitude lines. Usually drawn for a particular tidal constitutent or tidal condition (eg mean spring tides).
Cordillera	An entire mountain province, including all the subordinate ranges and groups and the interior plateaux and basins.
Coriolis Force	An apparent force acting on a body in motion, due to the rotation of the Earth, causing deflection (eg of winds and currents), to the right in the N hemisphere and to the left in the S hemisphere.
Co-Tidal Chart	A chart combining co-range lines with co-tidal lines; co-tidal charts may refer to the tide as a whole or to one or more tidal constituents.
Co-Tidal Lines	Lines joining points at which high water (or low water) occurs simultaneously. the times may be expressed as differences from times at a standard port or as intervals after the time of Moon's transit.
Course	The intended direction of the ship's head.
Course Made Good	The resultant horizontal direction of actual travel. the direction of a point of arrival from a point of departure.
Cove	A small indentation in a coast (usually a cliffy one), frequently with a restricted entrance and often circular or semi-circular in shape.
Cradle	A carriage of wood or metal in which a vessel sits on a slipway.
Craft	A term applied to small vessels and boats.
Crane	A mechanical contrivance for lifting weights.
Crane Lighter	A lighter especially fitted with a crane. May be self-propelled or towed.
Crater	A bowl-shaped cavity; in particular, at the summit or on the side of a volcano.
Creek	A comparatively narrow inlet, of fresh or salt water, which is tidal throughout its course.
Crest	Of a hill, the head, summit or top: of a mountain range, the line joining the highest points. Similarly, of an elevation of the seabed, or of a swell or wave.
Cross-Sea	A wave formation imposed across the prevailing waves. See also confused sea.
Cross-Swell	Similar to cross-sea but the waves are longer swell waves.
Culvert	A tunnelled drain or means of conveying water beneath a canal, railway embankment or road (sometimes the size of a small bridge, ie up to about 3 m across). Also, a channel for electric cables.
Current	The non-tidal horizontal movement of the sea which may be in the upper, lower or in all layers. in some areas this movement may be nearly constant in rate and direction while in others it may vary seasonally or fluctuate with changes in meteorological conditions. the term is often used improperly to denote tidal streams.
Cut	The intersection on the chart of two or more position lines. An opening in an elevation or channel. Similar to a canal but shorter. May constitute a straightening of a bend in a winding channel.
Cut Tide	A tide which fails to reach its predicted height at high water.
Dam	A bank of earth or masonry, etc, built to obstruct the flow of water, or to contain it.
Dan Buoy	An anchored float, ballasted to float upright, carrying a stave through its centre with a flag, a light or other distinguishing mark.
Danger	The term is used to imply a danger to surface navigation.
Danger Angle: Horizontal or Vertical	The angle subtended at the observer's eye, by the horizontal distance between two objects or by the height or elevation of an object, which indicates the limit of safe approach to an off-lying danger.
Danger Line	A dotted line on the chart enclosing, or bordering, an obstruction, wreck, or other danger.
Date Line	The International Date Line, accepted by international usage, is a modification of the 180° meridian to include islands of any group, etc on the same side of the line. Its position is shown on Chart 5006 - the World - Time Zone Chart and described in the relevant ALRS. When the Date Line is crossed on an E course the date is put back one day, on a W course the date is advanced one day.
Daybeacon	A term used in the USA and Canada for a beacon: in the USA it is restricted to unlighted beacons.
Daymark	Large unlit beacon. Term also used to denote an unlit topmark or other distinguishing mark or shape incorporated into a beacon, light-buoy or buoy.
Deep	A relatively small area of greater depth than its surroundings, primarily used for the deeper parts of the great ocean trenches. See also hole.
Deep-Water Route	A route within defined limits which has been accurately surveyed for clearance of sea bottom and submerged obstacles as indicated on the chart. See also recommended track.
Defile	A narrow mountain pass or gorge.
Degaussing Range	An area about 2 cables in extent set aside for measuring ship's magnetic fields. Sensing instruments are installed on the seabed in the range with cables leading to a control position ashore. the range is usually marked by buoys.
Degenerate Amphidrome	A terrestial point on a tidal chart from which co-tidal lines appear to radiate.
Delta	A tract of alluvial land, generally trianglular, enclosed and traversed by the diverging mouths of a river.
Departure; Point Of	The last position fixed relative to the land at the beginning of an ocean voyage of passage.
Depth	The vertical distance from the sea surface to the seabed, at any state of the tide. Hydrographically, the depth of water below chart datum. See also sounding.
Derrick	A contrivance for hoisting heavy weights. Usually consisting of a wooden or metal spar with one end raised by a topping lift from a post or mast and the other end pivoted near the base.
Deviation Dolphin	Dolphin which a ship may swing around for compass adjustment.
Diatom	Microscopic phytoplankton, especially common in the polar seas; develops delicate cases of silica.
Diatom Ooze	A siliceous deep-sea ooze formed of the shells of diatoms.
Diffuser	An arrangement of multiple outlets for distributing liquid at the seaward end of a pipeline or outfall.
Dilution of Precision	A dimensionless number that takes into account the contribution of relative satellite geometry to errors in position determination.
Directional Radiobeacon	A radiobeacon which transmits two signals in such a way that they are of equal strength on only one bearing.
Diurnal Inequality	The inequality, either in the heights of successive high waters or in the intervals between successive high or low waters.
Diurnal Stream	A tidal stream which reverses its direction once during the day.
Diurnal Tide	A tide which has only one high water and one low water each day; that part of a tide which has one complete oscillation in a day.
Dock	The area of water artificially enclosed in which the depth of water can be regulated. Also used loosely to mean a tidal basin.
Dock Sill	The horizontal masonry or timber work at the bottom of the entrance to a dock or lock against which the caisson or gates close. the depth of water controlling the use of the dock is measured at the sill.
Docks	The area comprising the basins, quays, wharves, etc, and offices of a port; the dock area.
Dockyard	That part of a port which contains the facilities for building or repairing ships.
Dolphin	A built-up post, usually of wood, erected on shore or in the water.
Double Tide	A tide which, due to a combination of shallow water effects, contains either two high waters or two low waters in each tidal cycle. At Hook of Holland, this phenomenon occurs with the low waters and is known as the Agger.
Downstream	In particular, the direction in which the stream is flowing; in general, in rivers and river ports, whether tidal or not, the direction to seaward.
Drag	A ship is said to drag (her anchor) if the anchor will not hold her in position. Also commonly used by seamen to describe the retardation of a ship caused by shallow water.
Drag Sweep	To tow a wire or bar set horizontally beneath the surface of the water to determine the least depth over an obstruction or to ascertain that a required minimum depth exists in a channel. Used as a noun, to denote the apparatus for this.
Dredge	To deepen or attempt to deepen by removing material from the bottom. Also an apparatus for bringing up bottom samples, gathering deep water organisms, etc.
Dredged Area	Area where the depths have been increased by the removal of material from the bottom.
Dredger or Dredge	A special vessel fitted with machinery for dredging, employed in deepening channels, harbours, etc, and removing obstructions to navigation such as shoals and banks. the various types include: Bucket dredgers, Grab dredgers and Suction dredgers.
Dredging Anchor	A vessel is said to be dredging anchor when moving, under control, with her anchor moving along the seabed.
Dries	A feature which is covered and uncovered by the tide is said to dry. the drying height is the height above chart datum, which is indicated on charts by a bar under the figure, or the legend "Dries" which may be abbreviated to "Dr". See also awash.
Drift	The distance covered by a vessel in a given time due solely to the movement of current or tidal stream, or both. Also, a detached and floating mass of soil and growth torn from the shore or river bank by floods, often mistaken for a islet. (Common in the East Indies). (verb) To move by action of the wind and current without control.
Drift Angle	The angle between the ground track and water track.
Drift Current	A horizontal movement in the upper layers of the sea, caused by wind.
Drilling Rig	A movable float platform used to examine a possible oil or gasfield.
Drillship	A ship specially designed for offshore drilling of the seabed.
Dry Bulk Container	For cargoes such as dry chemicals or grain.
Dry Cargo Container	For general cargo.
Dry Dock	An excavation in the ground, faced with masonry or concrete, into which a ship is admitted for underwater cleaning and repairs. the entrance can be closed by a caisson or gate. the water is pumped out after a vessel has entered, leaving her dry, resting on blocks and generally also supported by shores. Sometimes called a "graving dock". See also Floating Dock.
Dry Harbour	A small harbour which dries out, or nearly so, at LW. Vessels using it must be prepared to take the ground on the falling tide.
Drying Heights	Heights above chart datum of features which are periodically covered and exposed by the rise and fall of the tide. See also awash.
Dumb Lighter	A lighter incapable of self-propulsion.
Dumping Ground	An area similar to a spoil ground.
Dune	A ridge or hill of dry wind-blown sand which may, or may not, be in a state of migration. Vegetation (frequently planted on purpose) often stabilises previously migrating dunes. Coastal dunes may occur in the vicinity of sandy shores, but cannot survive wave action consequently they are features of the coastland rather than of the foreshore.
Duration (of Rise or Fall of the Tide)	The time interval between successive high and low waters.
Dyke or Dike	A causeway or loose rubble enbankment built in shallow water in a similar way to a training wall, but not necessarily for the same purpose. Sometimes built across shallow banks at the side of an estuary to stabilise the sandbanks by protection against wave action, and to prevent silting in the channel. in the Netherlands: an embankment to prevent flooding and encroachment by the sea. In Orkney and Shetland Islands: a wall. Also used to mean an artificial ditch.
Ebb Tide	A loose term applied both to the falling tide and to the outgoing tidal stream.
Eddy	A circular motion in water; a horizontal movement in a different direction from that of the general direction of the tidal stream in the vicinity, caused by obstructions such as islands, rocks, etc, or by the frictional effects of beaches, banks, breakwaters, etc.
Elbow	A change of direction in the contour of a submerged bank or shoal; a sharp change in the direction of a channel, breakwater, pier, etc.
Elevation	That which rises above its surroundings, such as a hill, etc. On a chart, the elevation of a feature is its height above the level of MHWS or MHHW. See also heights.
Embankment	A sloping structure of stone, rubble or earth, raising the height of a river bank, or used as the foundation for, or strengthening of, a causeway or dyke.
Embayed	To be in such a position, or under such adverse conditions, in a bay that extrication is difficult if not impossible.
Entrance Lock	A lock situated between the tideway and an enclosed basin when their levels vary. It has two sets of gates by means of which vessels can pass either way at all states of the tide. Sometimes known as a Tidal lock.
Equilibrium Tide	The hypothetical tide which would be produced by the lunar and solar tidal forces in the absence of ocean constraints and dynamics.
Equinoctial Spring Tide	A spring tide (greater than average) occurring near the equinox (in March and September).
Equinox	Either of the two points at which the Sun crosses the equator: or the dates on which these occurrences take place.
Erosion	The wearing away of the coast (or banks of a river) by water action; the opposite of accretion.
Escarpment	An elongated and comparatively steep slope separating flat or gently sloping areas.
Established Direction of Traffic Flow	A traffic flow pattern indicating the directional movement of traffic as established within a Traffic Separation Scheme.
Estuary	An arm of the sea at the mouth of a tidal river, usually encumbered with shoals, where the tidal effect is influenced by the river current.
Estuary Port	A port built at the tidal mouth or estuary of a river.
Even Keel	The state of a ship when her draught forward and aft are the same. Loosely applied when a ship is floating at her designed draught marks.
Examination Anchorage	One used by ships while awaiting examination.
Eyot	A small island in a river.
Fairway	The main navigable channel, often buoyed, in a river, or running through or into a harbour.
Falling Tide	The period between high water and the succeeding low water.
Fan	A relatively smooth feature normally sloping away from the lower termination of a canyon or canyon system. Also termed a Cone.
Fathom	A unit of measurement used for soundings. Equal to 6 feet or 1·8288 m.
Fathom Lines	Submarine contour lines drawn on charts, indicating equal depths in fathoms.
Ferry	A boat, pontoon, or any craft, used to convey passengers or vehicles to and fro across a harbour, river, etc. See also train ferry.
Fetch	The area of the sea surface over which seas are generated by a wind having a constant direction and speed. Also, the length of the generating area, measured in the direction of the wind, in which the seas are generated.
Fish Aggregating Device	A general term used to designate fish havens, marine farms, etc.
Fish Haven	An area where concrete blocks, hulks, disused car bodies, etc, are dumped to provide suitable conditions for fish to breed in. Devices may also be moored in mid-water or on the surface to serve the same purpose. In Japanese waters, the term "floating fish haven" may be used instead of marine farm. Draught permitting, vessels may navigate over seabed fish havens, but they are hazards to anchoring or seabed operations.
Fish Pound	A barrier across the mouth of a creek placed to retain fish in a creek.
Fish Stakes	A row of stakes set out from the shore, frequently to a considerable distance; often terminating in a partly decked enclosure from which a net can be lowered.
Fish Trap	An enclosure of stakes set in shallow water or a stream as a trap for fish.
Fish Weir	An enclosure of stakes set in a stream or on the shoreline as a trap for fish.
Fishing Ground	Area wherein craft congregate to fish; most particularly those areas occupied periodically by the large fishing fleets.
Fishing Harbour or Port	One especially equipped for the convenience of the fishing industry, the handling of fish and the maintenance of its vessels.
Fitting-Out Basin	A basin in a shipyard sited and equipped, to accommodate ships to complete the installation of machinery, etc, after launching.
Fix	The position of the ship determined by observations.
Fixed Crane	Built on the shore for use in one place only.
Flat	An extensive area, level or nearly so, consisting usually of mud, but sometimes of sand or rock, which is covered at high water and is attached to the shore. Sometimes called Tidal flats. See also ledge.
Flat Rack Container	For timber, large items or machinery.
Floating Beacon	A moored or anchored floating mark ballasted to float upright, usually displaying a flag on a tall pole, and sometimes carrying a light or radar reflector; used particularly in hydrographic surveying.
Floating Bridge	A power-worked pontoon used as a ferry which propels itself across a harbour, river, canal, etc, by means of guide chains.
Floating Crane	Mounted on a lighter or pontoon. See also crane lighter.
Floating Dock	A watertight structure capable of being submerged sufficiently, by admission of water into the pontoon tanks, to admit a vessel. the tanks are then pumped out, the dock and vessel rising until the latter is clear of the water, thus serving the same purpose as a dry dock.
Flood Channel	A channel in tidal waters through which the flood (incoming) tidal stream flows more strongly, or for a longer duration of time, than the ebb. It is characterised by a sill or bar of sand or other consolidated matter at the inner end, ie the least depth in the channel occurs close to the inner end. Ebb channels occur in close association with, and usually alongside, flood channels: they have a sill at their outer end.
Flood Tide	A loose term applied both to the rising tide and to the incoming tidal stream. See also ebb tide.
Flood-Mark	A mark, consisting usually of a horizontal line and a date, sometimes found on riverside buildings, dock walls, etc, to mark the highest level reached by flood waters at the date indicated.
Flow	The combination of tidal stream and current; the whole water movement. Also a loose term for flood (eg ebb and flow).
Following Sea	One running in the same direction as the ship is steering.
Foraminifera	Single-celled animals consisting of a mass of jelly-like flesh with no definite organs or parts of the body; covered with a casing of carbonate of lime: common in the surface waters of the sea.
Forced Tide	A tide which exceeds its predicted height at high water.
Foreland	A promontory or headland.
Foreshore	A part of the shore lying between high and low water lines of Mean Spring tides.
Form Lines	Lines drawn on a chart to indicate the slope and general shape of the hill features; generalised contour lines which do not represent any specific or standardised heights. See also hachure.
Foul Area, Foul Bottom or Foul Patch	An area where the seabed is strewn with wreckage or other obstructions, no longer dangerous to surface navigation, but making it unsuitable for anchoring.
Foul Ground	An area where the holding qualities for an anchor are poor, or where danger of striking or fouling the ground or other obstructions exist.
Fracture Zone	An extensive linear zone of irregular topography of the sea floor, characterised by steep-sided or asymmetrical ridges, troughs or escarpments.
Free Port	A port where certain import and export duties are waived (unless the goods pass into the country), to facilitate re-shipment to other countries. See also transit port.
Freshet	An abnormal amount of fresh water running into a river, estuary or the sea, caused by heavy or prolonged rain or melted snow.
Fringing Reef	A reef, generally coral, closely attached to the shore with no lagoon or passage between it and the land.
Furrow	Oceanographically, a fissure which penetrates, roughly perpendicularly to the run of the contours, into the continental or island shelf or slope. See also canyon.
Gangway	Similar to a brow when it is sometimes called a gangplank. Also, the actual opening in the ship's side by which a ship is entered or left. Also, a passage-way in a ship.
Gantry Crane	Mounted on a frame or structure spanning an intervening space. See also Transporter.
Gap	Oceanographically, a break in a ridge or rise.
Gat	A swashway, gut or natural channel through shoals.
Geodesic	The shortest distance between two points on the spheroid. It is equivalent to a great circle on the sphere.
Geographical Mile	The geographical mile is the length of 1 minute of arc, measured along the equator; its value is determined by the dimensions of the spheroid in use.
Geoid	An imaginary surface which is everywhere perpendicular to the plumb line, and which on average coincides with Mean Sea Level in the open ocean. Its shape approximates to that of a spheroid, but it is irregular due to the uneven distribution of the Earth's mass.
Gird	To gird a ship is to prevent her from swinging to wind and tide. of a tug, to be towed broadside on through the water by her tow-rope.
Global Navigation Satellite System (Glonass)	The satellite navigation system owned and operated by the Russian Federation.
Global Positioning System (Gps)	The satellite navigation system owned and operated by the United States Department of Defense.
Globigerina Ooze	Ooze which has the limy skeletons of foraminifera as its principal constituent, the dominant element being the calcareous tests of the globigerina (a spherical shelled organism).
Godown	A term used in Eastern ports for a warehouse or store.
Gong-Buoy	A buoy fitted with a gong which may be actuated automatically or by wave motion.
Gradient Currents	Currents caused by pressure gradients in the water.
Gravel	Coarse sand and small water-worn or rounded stones; varying in size from about the diameter of the top of a man's thumb to the size of a pinhead. See also sand, pebbles.
Graving Dock	Another name for a dry dock. To grave is an old term meaning to burn off the accretions on a ship's bottom before tarring, etc.
Grid	A systematic rectangular network of lines superimposed on a chart or map and lettered and numbered in such a way that the position of any feature can be defined with any required degree of precision.
Grid Reference	The position of a feature given in grid letters and numbers.
Gridiron	A flat framework, usually baulks of timber placed parallel with each other, erected on the foreshore below the high water line, and in such a position that a vessel can be moved over it at high water and left dry and resting on it at low water.
Ground	A portion of the Earth's crust which may be submerged or above water, eg spoil ground, middle ground, swampy ground, landing ground.
Ground Speed	The speed of a vessel over the ground.
Ground Swell	A long ocean swell; also this swell as it reaches depths of less than half its length and becomes shorter and steeper; ie influenced by the ground.
Groyne	A low wall-like structure, generally of wood or stone, usually extending at right angles from the shore, to prevent erosion. Frequently erected in estuaries and rivers to direct the flow of the water and prevent silting or encourage accretion.
Gulf	A portion of the sea partly enclosed by land; usually of larger extent and greater relative penetration than a bay.
Gut	A natural narrow inlet of deep water in a bank or shoal, sometimes forming a channel through it. It may also refer to the main part of a channel.
Hachures	Shading lines sometimes used on charts and maps to indicate the general slope and shape of hill forms. See also form lines.
Half-Tide	The height of the tide halfway between high water and low water. See also. mean tide level.
Half-Tide Basin	A basin the gates of which are open for entry and departure some hours before and after high water.
Half-Tide Rock	Formerly used to describe rocks which are awash at about mean tide level.
Handy Craft	An easily manoeuvred boat.
Harbour	A stretch of water where vessels can anchor, or secure to buoys or alongside wharves, etc, and obtain protection from sea and swell. the protection may be afforded by natural features or by artificial works. See also artificial harbour, island harbour.
Harbour Craft	Boats, barges, lighters, etc, used on harbour work.
Harbour Reach	Reach of a winding river or of an estuary which leads directly to the harbour.
Hard	A strip of gravel, stone or concrete, built on a beach across the foreshore to facilitate landing or the hauling up of boats.
Harmonic Analysis	An analysis of tidal observations, carried out to determine the harmonic constituents of the tide, as a basis for tidal predictions.
Harmonic Prediction	Prediction of the tide by combining harmonic constituents.
Haven	A harbour or place of refuge for vessels from the violence of wind and sea. in the strict sense it should be accessible at all states of the tide and conditions of weather.
Head	A comparatively high promontory with a steep face. An unnamed head is usually described as a headland. Also, the inner part of a bay, creek, etc, eg the head of the bay. Also, the seaward end of a jetty, pier, etc.
Head Sea	A sea coming from the direction in which a ship is heading; the opposite to a following sea.
Heading	Synonymous with ship's head.
Headway	Motion in a forward direction. Also, an obsolescent term synonymous with vertical clearance.
Heavy Sea	A rough, high sea.
Height	The vertical distance between the top of an object and its base. On Admiralty charts, the term "height" (except in the case of drying heights) is used in the sense of elevation and unless otherwise stated, is expressed, in metres or feet as appropriate, above the level of MHWS, MHHW, or, in places where there is no tide, above the level of the sea. See also elevation, High Water Datum. Also, the height of a vessel is the height of the highest point of a vessel's structure (e.g radar aerial, funnel, cranes, masthead) above her waterline.
Height of the Tide	The vertical distance at any instant between sea level and chart datum.
Heights	A comparatively level plateau at the summit of a precipitous mountain.
High Focal Plane Buoy	A light-buoy on which the signal light is fitted particularly high above the waterline. Used as fairway or landfall buoys. See also lanby.
High Water (Hw)	The highest level reached by the tide in one complete cycle.
High Water Datum or Datum For Heights	The high water plane to which elevations of land features are referred. On Admiralty charts this datum is normally the level of MHWS when the tide is predominantly semi-diurnal, or MHHW when the tide is predominantly diurnal.
High Water Stand	A prolonged period of negligible vertical movement near high water, this being a regular feature of the tides in certain localities while in other places stands are caused by meteorological conditions.
Higher High Water	The higher of two successive high waters where diurnal inequality is present.
Highest Astronomical Tide (Hat)	The highest tidal level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions.
Holding Ground	The sea bottom of an anchorage is described as good or bad holding ground according to its capacity for gripping the anchor and chain cable. in general, clay, mud and sand are good; shingle, shell and rock are bad.
Hole	A small area of considerably greater depths than those in the vicinity; of less area than a deep.
Hollow Sea	A very deep and steep sea.
Hopper	A barge used in harbours, etc, for conveying sullage or spoil to a spoil ground (where it is discharged through the bottom of the barge).
Horizontal Datum	A reference for specifying positions on the Earth's surface. Each datum is associated with a particular reference spheroid. Positions referred to different datums can differ by several hundred metres.
Hydrography	The science and art of measuring the oceans, seas, rivers and other waters, with their marginal land areas, inclusive of all fundamental elements which have to be known for the safe navigation of such areas, and the publication of such information in a form suitable for the use of navigators.
Impounding Basin	A basin in which water can be held at a certain level, either to keep craft afloat or to provide water for sluicing.
Impounding Basin	A basin in which water can be held by means of a sluice, weir or gate. Used for keeping craft afloat when the tide drops below a certain level, or to provide water for sluicing a channel which is very shallow and tends to collect silt.
Index Chart	An outline chart on which the limits and numbers of navigational charts, volumes of Admiralty Sailing Directions, etc, are shown.
Indian Spring Low Water	A level, originally devised by Sir George Darwin for use in Indian waters, determined from harmonic constants and used as chart datum in some parts of the world.
Inland Waterways	The navigable systems of waters comprising canals, rivers, lakes, etc, within the land territory.
Inlet	A small indentation in the coastline usually tapering towards its head. See also creek.
Inner Harbour	A harbour within a harbour, provided with quays, etc, at which vessels can berth.
Inshore	Close to the shore. Used sometimes to indicate shoreward of a position in contrast to seaward of it.
Inshore Traffic Zone	A routing measure comprising a designated area between the landward boundary of a Traffic Separation Scheme and the adjacent coast, to be used in accordance with the provisions of the International Regulations for Preventing Collisions at Sea 1972.
International Nautical Mile	The international nautical mile is 1852 m. the unit used by the United Kingdom until 1970 was the British Standard nautical mile of 6080 feet or 1853·18 m.
Ironbound Coast	A rock-bound coast without anchorage or harbour.
Island Harbour	A harbour formed, or mainly protected, by islands.
Island Shelf	The zone around an island and extending from the low water line to a depth at which there is usually a marked increase in slope towards oceanic depths.
Island Slope (Shoulder or Talus)	The declivity from the outer edge of the island shelf into deeper water.
Island Terminal or Structure	Deep-water structure not connected to the shore by a causeway or jetty. Submarine pipelines or overhead cableways are used to transport cargoes between the island and the shore.
Isobathic	Of equal depth.
Isogonic	Of equal magnetic variation (declination).
Jetty	A structure generally of wood, masonry, concrete or iron, which projects usually at right-angles from the coast or some other structure. Vessels normally lie alongside parallel with the main axis of the structure. Also, term used in the USA and Canada for a training wall.
Knot	The nautical unit of speed, ie 1 nautical mile (of 1852 m) per hour.
Lagoon	An enclosed area of salt or brackish water separated from the open sea by more or less, but not completely, effective obstacles, such as low sandbanks. The name is most commonly used for the area of water enclosed by a barrier reef or atoll.
Lanby (Large Automatic Navigational Buoy)	A very large light-buoy, used as an alternative to a light-vessel, to mark offshore positions important to the mariner. Lanbys vary in size up to a displacement of 140 tonnes and a diameter or height of 12 m. Radiobeacons, racons or radar reflectors may be fitted to them. See Admiralty List of Lights.
Land Levelling System	A network of benchmarks, etc, connected by levelling to a common datum.
Land Survey Datum	The point of origin of a land levelling system giving the plane to which elevations of features shown on maps are referred. the most usual plane for land survey datums is an approximation to MSL.
Landfall	The first sight of radar indication of land at the end of a passage.
Landfall Buoy	A buoy with a tall superstructure, marking the seaward end of the approach to a harbour or estuary. It may be situated out of sight of land.
Landing	A place where boats may ground in safety; a contraction of "landing place used by boats". May be artificial, consisting of a platform or steps, or the equivalent in natural rock.
Landing Stage	A platform or pontoon connected with the shore, for landing or embarking passengers or goods. Ships can berth alongside the larger landing stages.
Landlocked	Sheltered by land from all or very nearly all directions.
Landmark	A prominent artificial or natural feature on land such as a tower or church, used as an aid to navigation.
Landslip	Sliding down of a mass of land on a cliff, mountain or cutting.
Launching	The sliding of a newly-built ship by the action of its own weight into the water down on a specially prepared slipway-stern first or beam on (side launch).
Launching Cradle	The frame in which a ship is supported for launching.
Lava	An igneous rock. It is formed by the cooling of magma (ie matter flowing from a volcano or fissure in the ground) on the Earth's surface.
Layering	A method of emphasising on a chart differences of height or depth by the use of varying tints.
Lead	Lead (Pronounced "led"). the weight used in sounding with a leadline. (Pronounced "leed"). A narrow channel; especially through pack ice, or in rock or coral-studded waters.
Leading Lights	Lights at different elevations so situated as to define a leading line when brought into transit.
Leading Line	A suitable line for a vessel to follow through a given area of water as defined by leading marks located on a farther part of the line.
Leading Mark	One of a set of two or more navigation marks that define a leading line.
Ledge	A flat-topped ridge or narrow flat of rocks, extending from an island or coast. See also shelf.
Lee Shore	The shore towards which the wind is blowing.
Lee Side	The side of the ship or object which is away from the wind and therefore sheltered.
Lee Tide	A tidal stream running in the same direction as the wind is blowing.
Levee	Large river embankment built to prevent flooding. A naturally raised river bank built up by flood deposit. Oceanographically, an embankment bordering a canyon, valley or channel.
Light Aboard Ship (LASH)	A cargo-carrying system using specially built ships and lighters. Cargoes are loaded into LASH lighters which are towed to a LASH ship where the loaded lighters are embarked. At their destination the LASH lighters are disembarked and towed away to their unloading berths. Special berths or anchorages are sometimes designed for LASH ships.
Light-Beacon	A beacon from which light is exhibited. See also buoyant beacon.
Light-Buoy	A buoy carrying a structure from which is exhibited a light, which may have any of the characteristics of a light exhibited from a lighthouse other than sectors. See also lanby, light-float.
Lighter	A general name for a broad flat-bottomed craft used for transporting cargo and other goods between vessels and the shore. Lighters may be self-propelled but are usually towed. There are also lighters rigged for special purposes. See also dumb lighter, mooring lighter, crane lighter.
Light-Float	An unmanned fully-automated vessel, comparable in size to a light-vessel, or a boat-shaped unmanned float carrying a light and sometimes sounding a fog signal. the former is a major navigational light; the latter may sometimes be used instead of a light-buoy where there are strong tidal streams or currents.
Lighthouse	A distinctive structure from which a light or lights are exhibited as an aid to navigation.
Lighthouse Buoy	A name formerly used for a lanby.
Lights	A comprehensive term including all illuminated aids to navigation, other than those exhibited from floating structures.
Lights in Line	Two or more lights so situated that when in transit they define the limit of an area, the alignment of a cable, or an alignment for use of anchoring, etc. Unlike leading lights they do not mark a direction to be followed.
Light-Vessel (Sometimes Known As Light-Ship)	A manned vessel, secured in a designated locality carrying a light of high luminous intensity and usually sounding a fog signal to assist navigation.
Line of Bearing	A ship runs on a line of bearing if she makes good a ground track on a constant bearing of an object.
Linkspan	A pontoon carrying a ramp placed between a ro-ro vessel and a wharf to enable vehicles to embark or disembark from the wharf.
Liquid Natural Gas (LNG)	Gas, predominantly methane, from oilfield sources. Held in liquid state at atmospheric pressure at a temperature of about -162°C for transport and storage.
Liquid Petroleum Gas (LPG)	Light hydrocarbon material, gaseous at normal temperatures and pressures. By-product of petroleum refining and oil production. Held at liquid state under pressure for transport and storage. Liquid petroleum gases include propane and butane.
Local Knowledge	The use of a pilot, local seafarer competent to act as a pilot or past experience.
Local Magnetic Anomaly	A magnetic anomaly covering a small area.
Lock	An enclosure at the entrance to a tidal basin, or canal, with caissons or gates at each end by means of which ships are passed from one water level to another without materially altering the higher level.
Loom	The vague appearance of land, vessels, etc, when first sighted in darkness, or through fog, smoke or haze. Also, the diffused glow of a light seen when the light itself is below the horizon or obscured by an obstacle.
Low Water (Lw)	The lowest level reached by the tide in one complete cycle.
Lower Low Water	The lower of two successive LWs where diurnal inequality is present.
Lowest Astronomical Tide (Lat)	The lowest tidal level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions.
Luffing Crane	Can move a load nearer or farther from the base of the crane by raising or lowering the jib.
Lunitidal Interval	The time interval between the transit of the Moon and the next following high or low water; hence high water lunitidal interval, low water lunitidal interval, mean high water interval and mean low water interval.
Madrepore	A common form of perforate coral; probably the most wide-spread of reef-building corals.
Magnetic Anomaly	An effect, permanently superimposed on the Earth's normal magnetic field and characterised by abnormal values of the elements of compass variation, dip, and geomagnetic force. See also abnormal magnetic variation.
Magnetic Variation	The angle which the magnetic meridian makes with the true meridian. Called "magnetic declination" by physicists.
Main Ship Channel	The channel having the greatest depth and easiest navigation.
Mainland	A term applied to a major portion of land in relation to off-lying islands.
Make the Land	Make a landfall. To sight and approach the land after being out of sight of land at sea.
Manganese	A black mineral used in glass-making, etc, found as a bottom sediment.
Mangrove Swamp	A flat low-lying area of mud and silt, lying between the high and low water lines of spring tides, covered by the stilt-like roots of the mangrove and associated vegetation. A feature of tropical waters.
Marina	An area provided with berthing and shore facilities for yachts.
Marine Farm	A structure, on the surface or submerged, in which fish are reared or seaweed cultivated. They may obstruct navigation and are sometimes marked by buoys (special) which may be lighted. They are not necessarily confined to inshore locations and may be moved. See also fish haven, fish aggregating device.
Marine Protected Areas	Areas of inter-tidal or sub-tidal terrain together with their overlying waters and associated flora, fauna, historical and cultural features, which have been reserved to protect part or all of the enclosed environment. There is a wide variety of marine protected areas indicated in the terms used such as 'marine sanctuary', 'marine reserve', 'marine park', 'protected seascape' or 'wildlife sanctuary'.
Marine Railway	A term sometimes applied to a patent slip, more particularly in Canada and the USA.
Mark	A fixed feature on land or moored at sea, which can be identified on the chart and used to fix a ship's position.
Marl	A crumbling earthy deposit, particularly one of clay mixed with sand, decomposed shells, etc. A layer of marl is sometimes quite compact.
Mean High Water (Mhw)	The average of all high water heights, for a year as defined above. See also High Water. Hence Mean Low Water.
Mean High Water Neaps (Mhwn)	The height of mean low water neaps is the average, throughout a year when the average declination of the Moon is 23 1/2° of the heights of two successive high waters during those periods (approximately once a fortnight) when the range of the tide is least.
Mean High Water Springs (Mhws)	The height of mean high water springs is the average, throughout a year when the average maximum declination of the Moon is 23 1/2°, of the heights of two successive high waters during those periods of 24 hours (approximately once a fortnight) when the range of the tide is greatest.
Mean Higher High Water (Mhhw)	The height of the mean of the higher of the two daily high waters over a long period of time. When only one high water occurs on a day this is taken as the higher high water. Used where the tide is predominantly diurnal.
Mean Higher Low Water (Mhlw)	The height of the mean of the higher of the two daily low waters over a long period of time.
Mean Low Water Neaps (Mlwn)	The height of mean low water neaps is the average height obtained from two successive low waters during the same periods.
Mean Low Water Springs (Mlws)	The height of mean low water springs is the average height obtained by two successive low watrs during the same periods.
Mean Lower High Water (Mlhw)	The height of the mean of the lower of the two daily high waters over a long period of time.
Mean Lower Low Water (Mllw)	The height of the mean of the lower of the two daily low waters over a long period of time. When only one low water occurs on a day this is taken as the lower low water.
Mean Sea Level (Msl)	The average level of the sea surface over a long period, previously 18·6 years, or the average level which would exist in the absence of tides.
Mean Tide Level	The mean of the heights of MHWS, MHWN, MLWS and MLWN.
Measured Distance	The shortest distance between two or more sets of parallel transits set up on shore to determine the speed of a vessel. the length and direction of the distance are charted.
Median Valley	The axial depression of the mid-oceanic ridge system. Also called a Rift or Rift Valley.
Mid-Channel Controlling Depth	A depth which applies only to the middle half of the channel.
Moat	An annular depression that may not be continuous, located at the base of many seamounts, islands and other isolated elevations.
Mobile or Crawler Crane	Self-propelled on wheels or caterpillar tracks.
Mole	A breakwater alongside the sheltered side of which vessels can lie. Also, a concrete or stone structure, within an artificial harbour, at right-angles to the coast or the structure from which it extends, alongside which vessels can lie.
Monobuoy	Term formerly used for a Single Point Mooring.
Moor	To secure a vessel, craft, or boat, or other floating objects by ropes, chains, etc, to the shore or to anchors. Also, to ride with both anchors down laid at some distance apart, and the ship lying midway between them.
Mooring Buoy	A buoy of special construction which carries the ring of the moorings to which a vessel secures.
Mooring Dolphins	Dolphins which support bollards for a ships's mooring lines. the ship does not come in contact with them as they are set clear of the berth.
Mooring Lighter	A lighter especially fitted for handling, laying and weighing moorings.
Mooring Tower	A metal tower standing on the seabed to which ships can moor.
Moorings	Gear usually consisting of anchors or clumps, cables, and a buoy to which a ship can secure.
Morse Code Light	A light in which flashes of different duration are grouped in such a manner as to reproduce a Morse code character.
Mud	A sediment having predominance of grains with diameters less than 0·06 mm. The term is a general term referring to mixtures of sediments in water and applies to both clays and silts. The geological name is "lutite".
Narrows	A contracted part of a channel or river.
Natural Scale	The ratio between a measurement on a chart or map and the actual distance on the surface of the Earth which that measurement represents. It is expressed as a ratio with a numerator of one, eg 1/25 000 or 1:25 000.
Nature of the Bottom	The material of which the seabed is formed, eg mud, stones.
Nautical Twilight	The period between the end of civil twilight and the time when the Sun's centre is 12° below the horizon in the evening, and the period between the time when the Sun's centre is 12° below the horizon and the beginning of civil twilight in the morning. See also astronomical twilight.
Navigable	Affording passage for ships or boats. Also, capable of being navigated.
Navigation	The art of determining a ship's position and of taking her in safety from one place to another.
Neap Tide	A tide of relatively small range occurring near the time of the Moon's first and last quarters.
Neck (of Land)	A narrow isthmus or promontory.
No Bottom Sounding	A depth obtained at which the lead or sounder has not reached the bottom.
Nodal Point	The point of minimum tidal range in an amphidromic system. An amphidromic point.
Noise Range	An area set aside for measuring the underwater noise generated by a ship. Acoustic sensing instruments are installed on the seabed with cables leading to a control position ashore. the area is often marked by buoys.
Non-Tidal Basin	A basin closed by a caisson or gates to shut it off from open water, so that a constant level of water can be maintained in it. Also called a wet dock.
Nun Buoy	A buoy in the shape of two cones, base to base, and moored from one point so that the other is more or less upright. Used in the USA for a buoy with a conical or truncated conical-shaped top.
Observation Spot	A position at which precise astronomical observations for latitude and longitude have been obtained.
Obstruction	A danger to navigation, the exact nature of which is not specified or has not been determined.
Ocean	The great body of water surrounding the land masses of the globe, or more specifically one of the main areas into which the body of water has been divided by geographers. Any of the major expanses of salt water on the surface of the globe.
Ocean Swell	A swell encountered in the open ocean in great depths.
Oceanography	The study of the oceans especially of the physical features of the sea water and seabed and of marine flora and fauna.
Offing	The part of the sea distant but visible from the shore or from an anchorage.
Offshore	To seaward of, but not close to, the shore, as in "offshore fishing". Also, from the shore, as in "offshore wind". Oceanographically, the region extending seaward from the low water line of Mean Spring tides to the continental or island slope.
Offshore Installation	Any structure such as a drilling rig, production platform, wellhead, SPM, etc, set up offshore.
Ogival Buoy	A buoy with an arch-shaped vertical cross-section above the waterline.
On the Beam	An object is said to be on the beam, or abeam, if its bearing is approximately 90° from the ship's head.
Ooze	Very soft mud, slime; especially on the bed of a river or estuary. Oceanographically, fine-grained soft deposits of the deep-sea, formed from the shells and skeletons of planktonic animals and plants. See also diatom, globigerina ooze, pteropod ooze, radiolarian ooze.
Open	Two marks are said to be open when they are not exactly in transit.
Open Coast	An unsheltered, harbourless coast open to the weather.
Open Harbour	Unsheltered harbour, exposed to the sea.
Open Roadstead	An anchorage unprotected from the weather.
Open Water	Waters where in all circumstances a ship has complete freedom of manoeuvre. See also restricted waters.
Opening	A general term to indicate a gap or passage. eg an opening in a reef.
Ordnance Datum	The datum, or series of datums, established on the mainland and adjacent islands of the British Isles as the point of origin for the land levelling system.
Ordnance Datum (Newlyn)	This point of origin corresponds to the average value of MSL at Newlyn during the years 1915 to 1921.
Ordnance Survey	The Government survey of Great Britain; the responsible authority for Ordnance Survey maps.
Orthodrome	A great circle track.
Orthomorphic or Conformal Projection	Charts and maps on this type of projection have the property that small areas on the Earth's surface retain their shape on the chart or map, the meridians and parallels being at right-angles to one another and the scale at any one point being the same in all directions. Mercator's and stereographic projections are examples used in hydrography.
Outer Harbour	A sheltered area, even in bad weather, outside the harbour proper, the inner harbour and the docks.
Outfall	A narrow outlet of a river into the sea or a lake, as opposed to the opening out at a mouth. Also, the mouth of a sewer or other pipe discharging into the sea.
Outfall Buoy	Buoy marking the position where a sewer or other pipe discharges into the sea.
Overfalls	Also known as tide-rips. Turbulence associated with the flow of strong tidal streams over abrupt changes in depth, or with the meeting of tidal streams flowing from different directions.
Overtide	Harmonic constituents of short period, associated with shallow water effect.
Parallel of Latitude	Small circle on the Earth's surface parallel with the equator.
Pass	A comparatively narrow channel often with high ground or cliff on either side, and leading to a harbour or river. Also, a passage through or over a mountain range.
Passage	A navigable channel, especially one through reefs or islands. Also, a sea journey between defined points; one or more passages may constitute a voyage.
Patch	A portion of water or land which has distinctive characteristics, eg drying patch (of land, ground, sand, etc), shoal patch (of water), and discoloured patch (of water, rock, etc). In British hydrographic usage "patch" may be used as an alternative to "shoal", both being limited to a detached area which constitutes a danger.
Patent Slip	A cradle supported on carriages running on rails on the shore from about the level of High Water Springs to the level of Low Water Springs. the cradle can be run into the water to receive a small or medium-sized vessel and then hauled up until the vessel is clear of the water for bottom cleaning and repair.
Pay Off	A ship is said to pay off when her head falls away from the wind.
Pebbles	Water-rounded material of from 4 to 64 mm in size, ie from the diameter of the top of a man's thumb to the diameter of his clenched fist when viewed sideways.
Pens	A series of parallel jetties for berthing small craft.
Perch	A small beacon, often an untrimmed sapling, used to mark channels through mud flats or sandbanks; may or may not carry a topmark; often of an impermanent nature.
Perigree	The point in the orbit of the moon which is nearest to the Earth. When the Moon is in perigee the tidal range is increased. See also apogee.
Perigree Tide	A spring tide, greater than average, occurring when the Moon is in perigee.
Perihelion	The point in the orbit of a planet which is nearest to the Sun. See also aphelion.
Phase (of the Moon)	The appearance at a given time of the illuminated surface of the Moon.
Phosphorescence	The name formerly applied to bioluminescence.
Phytoplankton	The microscopic floating plant life of the oceans; the basic food source for most marine life.
Pier	A structure, usually of wood, masonry, concrete or iron, extending approximately at right-angles from the coast into the sea. The head, alongside which vessels can lie with their fore-and-aft line at right-angles to the main structure, is frequently wider than the body of the pier. Some piers, however, were built solely as promenades. Also used for the structure joining a wharf to the land. Piers. Supports for the spans of a bridge.
Pierhead	The seaward end of a pier, frequently set at right-angles to the pier in the form of a T or L.
Pile	A heavy baulk of timber or a column of reinforced concrete, steel or other material, driven vertically into the bed of the sea or of a river. It may be used to mark a channel or to serve as part support for construction work such as a pier, wharf or jetty.
Pile Beacon	A beacon formed of one or more piles.
Pile Fender	A pile driven loosely into the seabed in front of a wharf, etc, to absorb the shock of a vessel going alongside.
Pile Lighthouse	A lighthouse erected on a pile foundation.
Pile Moorings	Permanent moorings to which a vessel is secured fore and aft between piles.
Pillar Buoy	A buoy of which the part of the body above the waterline is a pillar, or of which the greater part of the superstructure is a pillar or a lattice tower.
Pilot	Person qualified to take charge of ships entering, leaving, and moving within certain navigable waters. The term Admiralty Pilot is commonly used to designate a volume of Sailing Directions published by the Hydrographic Office.
Pilotage	The conducting of a vessel within restricted waters. Also, the fee for the services of a pilot.
Pilotage Waters	Those areas covered by a regular pilotage service.
Pinnacle (Rock)	A rock, which may or may not be dangerous to navigation, rising sheer from the bottom of the sea, and of which no warning is given by sounding. Oceanographically, any high pillar or rock or coral, shaped like a tower or spire, standing alone or cresting a summit.
Pitch	Angular motion of a ship in the fore-and-aft plane. See also roll, scend.
Pitching	The facing of the sloping sides of a breakwater, which may be paved, or consist of stones, tetrapods or rubble.
Plain	Oceanographically, a flat gently sloping or nearly level region of the sea floor.
Plankton	Collective name for the microscopic floating and drifting plant and animal life found throughout the world's oceans. A distinction can be made between neretic (coastal) and oceanic (deep-water) plankton. See also phytoplankton, zooplankton.
Plateau	Extensive elevated region with level (or nearly level) surface. See also tableland. Oceanographically, a flat or nearly flat area of considerable extent which is relatively shallow, dropping off abruptly on one or more sides.
Point	A sharp and usually comparatively low piece of land jutting out from the coast or forming a turning-point in the coastline.
Point of Origin	A fixed point in a co-ordinate system or grid to which all measurements are referred.
Polyzoa	Minute creatures of the sea, which always live in colonies, some of which are small and branching and others large and with strong lime skeletons which give them the appearance of corals.
Pontoon	A broad, flat-bottomed floating structure (often of heavy timber baulks) rectangular in shape, used for many purposes in a port, as a ferry landing place, a pierhead, or alongside a vessel to assist in loading or discharging.
Port	A commercial harbour or the commercial part of a harbour in which are situated the quays, wharves, facilities for working cargo, warehouses, docks, repair shops, etc. the word also embraces, geographically, the city or borough which serves shipping interests. See also ports named after location, e.g canal port, seaport, river port, etc.
Port Authority	Persons or corporation, owners of, or entrusted with or invested with the power of managing a port. May be called a Harbour Board, Port Trust, Port Commission, Harbour Commission, Marine Department, etc.
Port Radio Stations	Port radio stations normally operate in the VHF band through which messages can be passed to Port Authorities. These messages are restricted to the movement, berthing and safety of ships, and in emergency to the safety of persons. Port radio stations may be associated with radar surveillance and traffic control centres in large ports.
Portal Crane	A type of gantry crane with vertical legs giving sufficient height and width for vehicles or railway trucks to pass between them.
Position Line	A line on a chart, representing a line on the Earth's surface, on which a ship's position can be said to lie, such as might be obtained from a single bearing, the observations of one heavenly body, or an arc of a range circle.
Pound (or Pond)	Small body of still water in the form of a camber or small basin in a dockyard, used for the storage of boats or other gear afloat. eg boat pound, timber pound.
Pratique	Licence to hold intercourse with the shore granted to a vessel after quarantine or on showing a clean bill of health.
Precautionary Area	A routing measure comprising an area within defined limits where ships must navigate with particular caution and within which the direction of traffic flow may be recommended.
Predominant Direction	The mean direction within a continuous 90° sector containing the highest proportion of observations from all sectors, used on current diagrams.
Pressure Tide Gauge	An instrument which measures the pressure below the sea surface; this pressure may be converted to water depth if the air pressure, the gravitational acceleration and the water density are known.
Production Platform	A permanently-manned offshore structure sited on an oil or gasfield.
Project Depth	The design dredging depth of a channel.
Projection	A geometrical representation on a plane or a part of the Earth's surface.
Prominent Object	An object which is easily identifiable, but does not justify being classified as conspicuous.
Province	Oceanographically, a region identifiable by a group of similar physiographic features whose characteristics are markedly in contrast with surrounding areas.
Pteropod Ooze	Limy deposits formed from the dead bodies of small swimming snails or sea butterflies, commonest near the equator. Found in shallower water than globigerina ooze, and especially near coral islands an on submerged elevations far from land.
Pumice	A light, porous or cellular type of lava, occasionally to be found floating on the sea surface.
Quadrature	A term applied principally to the Sun and Moon when their longitudes differ by 90° (ie halfway between full and new Moon).
Quarantine	Isolation imposed on an infected vessel. All vessels are considered to be in quarantine until granted pratique.
Quarantine Anchorage	A special anchorage set aside, in many ports, for ships in quarantine.
Quartz	Crystalline silica. Usually colourless and transparent, but varies considerably in opaqueness and colour, the most common solid mineral.
Quay	A solid structure usually of stone, masonry or concrete (as distinguished from a pile structure) alongside which vessel may lie to work cargoes. It usually runs along or nearly along the line of the shore of the inner part of a port system.
Quayage	Comprehensive term embracing all the structures in a port alongside which vessels can lie. Also, the charge made for berthing on a quay. See also wharfage.
Quoin	A wedge; sometimes used to describe the shape of an island or hill.
Race	Fast-running water, frequently tidal, caused by passage through a constricted channel, over shallows, or in the vicinity of headlands, etc. Eddies are often associated with races.
Radar Assistance	The communicating to a vessel of navigational information determined by a shore radar, when requested.
Radar Conspicuous Object	Any object that is readily distinguishable and outstanding on a radar screen on most bearings from seaward.
Radio	Wireless Telegraphy (WT) and Telephony (RT). the internationally agreed prefix to all appliances operated by wireless or radio.
Radio Bearing	The bearing of a radio transmission.
Radio Fog Signal	Special transmissions provided by a radiobeacon as an aid to navigation during periods of fog and low visibility.
Radiobeacon	A radio transmitting station on shore or at an offshore mark, not necessarily manned, or light-buoy of whose transmissions a ship may take bearings. See also aero, circular, rotating pattern and directional radiobeacons.
Radiolaria	Forms of foraminifera having skeletons of silica.
Radiolarian Ooze	A siliceous deep-sea ooze formed of the skeletons of radiolaria.
Radome	A dome, usually of glass reinforced plastic, housing a radar aerial. On shore installations these domes are often conspicuous or prominent. Term is also used for domes or pods housing similar equipment in ships and on aircraft.
Raise the Land	To sight the land by approaching to the point where it appears above the horizon. Similarly, to raise a light or another ship.
Raised Beach	An old beach, raised appreciably beyond the inshore limit of wave action, by earth movements which have caused the sea to recede.
Ramp	A sloping road or pathway from the sea or river bed to above high water, in place of steps; eg the roadway from a beach to the top of a seawall. Also, an inclined platform between the shore and a vessel, with one end adjustable for height, to enable vehicles to drive on and off the vessel.
Range	Term used in the USA and Canada for transit.
Range of the Tide	The differences in level between successive high and low waters or vice versa.
Rate (of Tidal Streams and Currents)	The velocity, usually expressed in knots.
Ratio of Ranges	A factor, found on or deduced from a co-tidal chart, whereby the range of the tide offshore can be calculated.
Reach	A comparatively straight part of a river or channel, between two bends.
Recommended Direction of Traffic Flow	A traffic flow pattern indicating a recommended directional movement of traffic where it is impracticable or unnecessary to adopt an established direction of traffic flow.
Recommended Route	A route of undefined width, for the convenience of ships in transit, which is often marked by centreline buoys.
Recommended Track	A track shown on a chart, which all or certain vessels are recommended to follow. The best known track through an imperfectly charted area or through an intricate channel, or the best track for deep-draught vessels in shallow waters, or the route authorised for vessels of certain draught, are among the recommended tracks shown on charts. They are shown on charts by pecked lines, with arrows where necessary to show the direction to be followed, but where the tracks are defined by leading marks, whether charted or not, they are shown in firm lines. In a routing system, it means a route which has been specially examined to ensure so far as possible that it is free of dangers and along which ships are advised to navigate.
Rectilinear Stream	A tidal stream which runs alternatively in approximately opposite directions, with a period of slack water in between. See also rotary streams.
Reduction of Soundings	The adjustment of soundings to the selected chart datum by correction for the height of the tide, which gives charted depths.
Reef	An area of rocks or coral, detached or not, the depth over which constitutes a danger to surface navigation. Also, sometimes used for a low rocky or coral area, some of which is above water. Oceanographically, rocks lying at or near the sea surface.
Reflector	A device fitted to buoys and beacons to reflect rays of light.
Refrigerated Container	Insulated and usually fitted with its own refrigeration systems.
Refuge Harbour	An artificial harbour built on an exposed coast for vessels forced to take shelter from the weather.
Refuge Hut	A hut containing emergency rations and clothing, maintained on some barren and isolated coasts for the use of shipwrecked persons.
Reporting Point	A position in the approaches to certain ports where traffic is controlled by a vessel traffic service at which ships entering or leaving report their progress as directed in the relevant Admiralty List of Radio Signals. Also known by certain authorities as a Calling-in Point or Way Point.
Restricted Waters	Areas which, for navigational reasons such as the presence of sandbanks or other dangers, confine the movements of shipping to narrow limits, See also open waters.
Retroreflector	A surface or device from which most of the reflection of light can occur as retroreflection.
Rhumb Line or Loxodrome	Any line on the Earth's surface which cuts all meridians at the same angle, ie a line of constant bearing.
Ride To the Anchor	To lie at anchor with freedom to yaw and swing.
Ridge	Oceanographically, it has the three following means: A long narrow elevation with steep sides; A long narrow elevation often separating ocean basins. See also rise. The major oceanic mountain system of global extent.
Ripple Marks	Small ridges caused by wave action on sandy or silty shores, and on the seabed. See also backwash marks, beach cusps.
Rise	Oceanographically, a broad elevation that rises gently and generally smoothly from the sea floor. A synonym for the last-listed definition of ridge.
Rising Tide	The period between low water and high water.
River Basin	A region which contributes to the supply of water to a river or rivers. the catchment area of a river.
River Port	A port that lies on the banks of a river. See also canal port, seaport, estuary port.
Roads	An open anchorage which may, or may not, be protected by shoals, reefs, etc. Affording less protection than a harbour. Sometimes found outside harbours.
Roadstead	Alternative name for roads.
Rock	An extensive geological term, but limited in hydrography to hard, solid masses of the Earth's surface rising from the bottom of the sea, either completely submerged or projecting permanently, or at times, above water.
Roll	The angular motion of a ship in the athwartship plane. See also pitch.
Roll-On, Roll-Off (Ro-Ro)	Term applied to ships, wharves, berths and terminals, where vehicles can embark or disembark by driving on or off a vessel.
Root	The landward end of the structure of a jetty, pier, etc.
Rotary Streams	Tidal streams, the direction of which gradually turn either clockwise or anti-clockwise through 360° in one tidal cycle.
Rotating Pattern Radiobeacon or Radio Lighthouse	A radiobeacon which enables a ship to determine her true bearing in relation to it, without the use of direction-finding equipment. See the relevant Admiralty List of Radio Signals.
Roundabout	A routing measure comprising a separation point or circular separation zone and a circular traffic lane within defined limits. Traffic within the roundabout is separated by moving in a counterclockwise direction around the separation point or zone.
Routing System	Any system of one or more routes or routing measures aimed at reducing the risk of casualties; it includes traffic separation schemes, two-way routes, recommended tracks, areas to be avoided, inshore traffic zones, roundabouts, precautionary areas and deep-water routes.
Rubble	Waste fragments of stone, brick, concrete, etc, or pieces of undressed stone, used as a foundation or for protecting the sides of breakwaters and seawalls. See also pitching.
Run	The distance a ship has travelled through the water.
Runnel	A depression in a beach usually roughly parallel with the waterline for much of its course; frequently associated with rills debouching over the beach, but also occurring when there is a sudden change in the gradient, eg as caused by breakers during the stand of the tide near high or low water.
Running Survey	A survey in which the greater part of the work is done from the ship sounding and moving along the coast, fixed by dead reckoning, astronomical observations, or other means, and observing angles, bearings and distances to plot the general configuration of the land and offshore details. Similarly, a running survey of a river by boats.
Saddle	A low part, resembling in shape a saddle, in a ridge or between contiguous seamounts.
Saddlehill	A hill with two summits separated by a depression, appearing from some directions like a saddle.
Safe Overhead Clearance	The height above the datum of heights at which the highest point of a ship can pass under an overhead power cable without risk of electrical discharge from the cable to the ship.
Safety Fairway Anchorage	An anchorage adjacent to a shipping safety fairway.
Saltings	Lands in proximity to salt water, which are covered at times by the tide.
Sand	A sediment consisting of an accumulation of particles which range in size from a pin's head to a fine grain. the most common sediment on the continental shelves are of two principal types: Terrigenous sand which is made up from the breaking up of rocks on land by weathering, the small fragments being carried out to sea by streams. (The most common constituent of terrigenous sand is quartz, but many other minerals are also included). Calcarenite sand made up from shells or shell fragments, foraminifera, coral debris and other organisms that contain calcium carbonate. Also, a shoal area of sand, sometimes connected with the shore or detatched. Some sands partly dry and some are always submerged. Also see shifting sand.
Scale (On a Chart or Map)	A graduated line used to measure or plot distances. On large scale Admiralty charts the following scales are usually provided: Latitude and Distance, Feet, and Metres; and on ungraduated plans, Longitude. See also natural scale.
Scend or Send of a Ship	A ship is said to scend heavily when her bow or stern pitches with great force into the trough of the sea.
Scend or Send of Waves	The vertical movement of waves or swell alongside a wharf, jetty, cliff, rocks, etc.
Scoriae	Cellular lava or clinker-like fragments of it.
Scour	The clearing of a channel by the action of water. Also, the local deepening close to an islet, rock or obstruction due to the clearing action of the tidal streams or currents.
Scouring Basin	A backwater or basin by the side of a channel or small harbour from which water can be released quickly near low water for the purpose of scouring the channel or harbour.
Sea	The expanse of salt water which covers most of the Earth's surface. Also, a sub-division of the above, next in size to an ocean, partly and sometimes wholly enclosed by land, but usually with access to open water. Also, the waves raised by the wind blowing in the immediate neighbourhood of the place of observation at the time of observation.
Sea Mile	The sea mile is the length of 1 minute of arc, measured along the meridian, in the latitude of the position; its length varies both with the latitude and with the dimensions of the spheroid in use.
Sea Reach	The most seaward reach of a river or estuary.
Sea Room	Space clear of the shore which offers no danger to navigation and affords freedom of manoeuvre.
Seaboard	Alternative name for coastal region.
Seachannel	A long narrow U- or V-shaped shallow depression of the sea floor, usually occurring on a gently sloping fan or plain.
Seaknoll	An isolated submarine hill or elevation less promiment than a seamount.
Seamark	A daymark erected with the express purpose of being visible from a distance to seaward.
Seamount	A large isolated underwater elevation characteristically of conical form.
Seamount Chain	Several seamounts in a line.
Seamount Group	Three or more seamounts not in a line and with bases separated by a relatively flat sea floor.
Seamount Range	Three or more seamounts having connected bases and aligned along a ridge or rise.
Seapeak	A conical seamount.
Seaport	A port situated on the coast, with unimpeded connection with the sea. See also canal port, estuary port, river port.
Seasonal Changes (In Sea Level)	Variations in the sea level associated with seasonal changes in wind direction, barometric pressure, rainfall, etc.
Seawall	A solid structure, usually of masonry and earth, or tetrapods built along the coast to prevent erosion or encroachment by the sea. Ships cannot usually lie alongside a seawall.
Sea-Way	The open water outside the confines of a harbour. Also, a rough sea caused by wind, tide or both.
Sector of a Light	The portion of a circle defined by bearings from seaward within which a light shows a specified character or colour, or is obscured.
Semi-Diurnal (Stream or Tide)	Undergoing a complete cycle in half a day.
Separation Zone or Separation Line	A zone or line separating the traffic lanes in which ships are proceeding in opposite or nearly opposite directions; or separating a traffic lane from the adjacent sea area; or separating traffic lanes designated for particular classes of ships proceeding in the same direction.
Set (of the Stream)	The direction in which a tidal stream or current is flowing.
Shackle of Cable	The length of a continuous portion of chain cable between two joining shackles. in British ships the standard length of a shackle of cable is 15 fathoms (27·432 m).
Shallow	A shoal area in a river, or extending across a river, where the depths are less than those upstream or downstream of it.
Shallow Water Effect (Tidal)	A general term descriptive of the distortion of the tidal curve from that of a pure cosine curve, most marked in areas where there is a large amount of shallow water.
Sheer	A ship is said to take a sheer if, usually due to some external influence, her bows unexpectedly deviate from her course.
Shelf Edge or Shelf Break	A narrow zone at the outer margin of a shelf along which there is a marked increase of slope.
Shell	A hard outer case, conch, crust, or skeleton, of many sea animals.
Shifting Sand	Sand of such fine particles and other conditions that it drifts with the action of the water or wind.
Shingle	A descriptive term for gravel.
Ship Canal	A canal large enough to permit the passage of ocean-going vessels.
Ship's Head or Heading	The direction in which a ship is pointing at any moment.
Shiplift	An installation for dry docking vessels whereby they are raised clear of the water on a grid and cradle. Ship and cradle can then be transferred ashore on rails to a refitting area leaving the shiplift free to lift or refloat other vessels.
Shipping Lanes	Much frequented shipping tracks crossing an ocean or sea.
Shipping Safety Fairway	Area designated as a fairway by USA within which no artificial island or fixed structure, whether temporary or permanent is permitted.
Shipyard	A yard or place containing facilities in the way of slips and workshops, etc, for the construction, launching, fitting-out, maintenance and repair of ships and vessels.
Shoal	A detached area of any material the depth over which constitutes a danger to surface navigation. The term shoal is not generally used for dangers which are composed entirely of rock or coral. See also bank, shallow. Oceanographically, an offshore hazard to surface navigation composed of unconsolidated material.
Shore	The meeting of sea and land considered as a boundary of the sea. See also coast. Interchangeable with coast when used in a wide sense to denote land bordering the sea as seen from a vessel. See also foreshore. Also, a prop fixed under the ship's bottom or at her side, to support her in dry dock.
Shoreline	Another name for coastline, in a more general sense.
Sill	Oceanographically, the saddle of any submarine morphological feature which separates basins from one another. See also dock sill.
Sill Depth	The greatest depth over a sill.
Silt	Sediment deposited by water in a channel or harbour or on the shore, in still areas, or where an obstruction is met. A finer sediment than sand. See also clay.
Skerry	A rocky islet.
Slack Water	That period of negligible horizontal water movement when a rectilinear tidal stream is changing direction.
Slake	An accumulation of mud or ooze on the bed of a river, channel or harbour. Also, such an accumulation left exposed by the tide.
Slick	A local calm streak on the water caused by oil. Also, the calm patch left by the quarter of a ship when turning sharply.
Slime	Fine oozy mud or other substance of similar consistency.
Slip Dock	A combination of patent slip and dock (the water is excluded by gates and side walls) used where there is considerable range of the tide.
Slipway or Slips	Applied loosely to a building slip. A craft or small vessel under repair may be hauled on the slips to be clear of the water.
Snag	A small feature on the seabed capable of damaging nets and other fishing gear. Also called a fastener.
Solstices	The two points at which the Sun reaches its greatest declination N or S, or the dates on which this occurs.
Solstitial Spring Tide	The spring tide (greater than average) occurring near the solstices.
Sound	A passage between two sea areas. A passage having an outlet at either end. Also, an arm of the sea or large inlet.
Sounding	Measured or charted depth of water or the measurement of such a depth. See also reduction of soundings.
Spar-Buoy	A buoy in the form of a pole which is moored to float nearly vertical.
Speed	The speed of a vessel refers to her speed through the water unless otherwise specified. See also ground speed.
Spending Beach	The beach in a wave basin on which the waves entering the harbour entrance expend themselves, only a small residue penetrating the inner harbour.
Spherical Buoy	A buoy, the visible portion of which shows an approximately spherical shape.
Spheroid	A mathematically regular surface resembling a slightly flattened sphere, defined by the length of its axes and used to approximate the geoid in geodetic computations. eg Airy (used in Great Britain, International, etc).
Spindle Buoy	A buoy, similar in height to a spar buoy, but conical instead of cylindrical.
Spit	A long narrow shoal (if submerged) or a tongue of land (if above water), extending from the shore and formed of any material.
Spoil	Mud, sand, silt or other deposit obtained from the bottom of a channel or harbour, by dredging.
Spoil Ground	An area set aside, clear of the channel and in deep water when possible, for dumping spoil obtained by dredging, sullage, etc. A spoil ground buoy marks the limit of a spoil ground. Lesser depths may be found within the spoil ground.
Spring Tide	A tide of relatively large range occurring near the times of new and full Moon.
Spur	A projection from a range of mountains or hills or a cliff. Also, a small projection from a jetty or wharf, at an angle to its main axis. Oceanographically, a subordinate ridge or rise projecting outward from a large feature of elevation.
Stack	A precipitous detached rock of considerable height. Also, a pillar left when the roof of an arch collapses through continued weathering or wave action.
Staith or Staithe	A berth for ships alongside where the walls or rails project over the ship, enabling cargo (in most cases coal) to be tipped direct from the railway trucks into the vessel's holds.
Stand of the Tide	A prolonged period during which the tide does not rise or fall noticeably. in some cases this is a normal feature of the tidal conditions; in others it is caused by certain unusual meteorological conditions. See also high water stand.
Stand On	To continue on the same course.
Standard Time	The legal time common to a country or area, normally related to that of the time zone in which it wholly or partly lies. See the relevant Admiralty List of Radio Signals.
Statute Mile	The statute mile is the unit of distance of 1760 yards or 5280 feet (1609·3 m).
Steep-To	Any part of the shore or the sides of a bank or shoal which descends steeply to greater depths is described as a steep-to. Boat landings are described as steep-to when the gradient is steeper than about 1 in 6.
Steerage Way	The minimum speed required to keep the vessel under control by means of the rudder.
Stem the Tide	To proceed against the tidal stream at such a speed that the vessel remains stationary over the ground. Also, to turn the bows into the tidal stream.
Stippling	The graduations of shade or colour produced on a chart by means of dots.
Stones	A descriptive term for any loose piece of broken rock lying on the sea floor, ranging in size from that of pebbles to boulders. Used in place-names to indicate large detached rocks or islets, eg Seven Stones, Mewstone.
Storm Beach	A beach covered with coarse sand, pebbles, shingle or stones, as a result of storm waves above the foreshore, and usually characterised by berms or beach ridges.
Strait	A comparatively narrow passage connecting two seas or two large bodies of water.
Strath	Oceanographically, a broad elongated depression with relatively steep walls located on a continental shelf. the longitudinal profile of the floor is gently undulating with the great depths often found in the inshore portion.
Strip Light	A light whose source has a linear form, generally horizontal, which can reach a length of several metres. Used on heads of piers, along quay walls, at the corners of quays and on dolphins. It may have a rhythmic character and be coloured.
Submerged	A feature is said to be submerged if it has sunk under water, or has been covered over with water.
Sullage	Refuse, silt or other bottom deposit for disposal on a spoil ground, open sea, or some place clear of the channel.
Sullage Barge	The lighter or barge used for the conveyance of sullage.
Surf	The broken water between the outermost line of breakers and the shore. Also used when referring to breakers on a detached reef.
Surface Current	A current of variable extent in the upper few metres of the water column.
Surge	The difference in height between predicted and observed tides due to abnormal weather conditions. See Admiralty Tide Tables. See also positive surge, negative surge, storm surge.
Surging	The horizontal movement of a ship alongside due to waves or swell.
Suspended Well	An oil or gas well, not in use, but whose wellhead has been capped at the seabed for possible subsequent use.
Swamped Mooring	A non-operational mooring when the mooring buoy has been temporarily removed and the mooring chain lowered to the seabed.
Swash	The thin sheet of water sliding up the foreshore after a wave breaks. Also, a shoal in a tideway or estuary close enough to the surface to cause overfalls.
Swashway or Swatchway	A channel across a bank or through shoals. See also gut.
Sweep	Commonly used contraction of drag sweep.
Syzygy	An astronomical term denoting that two celestial bodies have the same celestial hour angle, or celestial hour angles differing by 180°. When the sun and Moon are in syzygy spring tides occur.
Tableknoll	A knoll having a comparatively smooth, flat top with minor irregularities.
Tableland	An extensive elevated region with a flat-topped level surface.
Tablemount	A seamount having a comparatively smooth, flat top. Also called a guyot.
Tank Farm	A large group of oil storage tanks, usually near an oil terminal or refinery.
Telegraph Buoy	A buoy marking the position of a submarine telegraph cable. See also cable buoy.
Terminal	A number of berths grouped together and provided with facilities for handling a particular form of cargo, eg oil terminal, container terminal, etc.
Terrace or Bench	A relatively flat horizontal or gently inclined surface, sometimes long and narrow, which is bounded by a steeper ascending slope on one side and by a steeper descending slope on the opposite side.
Tetrapods	Concrete masses the size of boulders, cast with four stump-legs so that the masses interlock. Used for the pitching of breakwaters and seawalls.
The Moorings	A place in which a vessel may be secured.
The Run of the Coast	The trend of the coast.
Tidal Angles and Factors	Astronomical data, combining the effects of several tidal constituents, used for the prediction of tides by the Admiralty Method. See Admiralty Tide Tables.
Tidal Basin	A basin without caisson or gates in which the level of water rises and falls with the tide. Sometimes called an open basin.
Tidal Gauge	An instrument which registers the height of the tide against a scale.
Tidal Harbour	A harbour in which the water level rises and falls with the tide as distinct from a harbour in which the water is enclosed at a high level by locks and gates.
Tidepole	A graduated vertical staff used for measuring the height of the tide.
Tide-Pools	Pools worn in seashore rocks, left full of water when the tide level has fallen below them.
Tide-Raising Forces	The forces exerted by the Sun and Moon which cause the tides.
Tide-Rode	An anchored or moored ship is tide-rode when heading into the tidal stream. See also wind-rode.
Tideway	Where the full strength of the tidal stream is experienced, as opposed to inshore where only weak tidal streams may be experienced. Also, the channel in which the tidal stream sets.
Time Signal	A special signal, usually by radio for the purpose of checking the errors of chronometers. See the relevant Admiralty List of Radio Signals.
Time Zones	Longitudinal zones of the Earth's surface each 15° in extent, for which a Zone Time is designated. the zones are shown on Chart 5006 (The World - Time Zone Chart) and described in the relevant Admiralty List of Radio Signals. See also Standard Time, Date Line.
To Beach	To run a vessel or boat ashore. To haul a boat up on a beach.
To Dock	To be admitted to a dock.
To Dock a Ship	To receive a ship into dock, or dry dock.
To Ferry	To convey in a boat, to and fro over a river, across a harbour, etc.
To Give a Wide Berth	To keep well away from another ship or any feature.
To Ground	To run ashore or touch bottom.
To Lock a Vessel	To pass a vessel through a lock.
To Open	To bring into view, eg "to open the land eastward of a cape".
To Run Before the Wind	To steer a course downwind.
To Run Down a Coast	To sail parallel with it.
To Shoal	To become more shallow.
To Shore Up	To support by means of shores round a vessel.
To Silt	To choke or be choked by silt.
To Sound	To determine the depth of water.
To Surge	A rope or wire is surged round the revolving drum of a winch when it is desired to maintain or ease the strain without heaving in at the speed of the winch.
To Warp	To move a ship from one place to another by means of a warp.
Tongue	A long, narrow and usually low, salient point of land. See also spit.
Topmark	An identification shape, fitted on the tops of beacons and buoys. See also daymark.
Topography	Detailed description or representation on a chart or map, of the natural and artificial features of a district. Also the features themselves.
Toroidal Buoy	A buoy shaped like a ring in the horizontal plane, usually with a central support with shape, mainly used for oceanographical purposes.
Track	The path followed, or to be followed, between one position and another. This path may be the ground track, over the ground, or the water track, through the water. Used in the sense of ground track in the term recommended track. Also used in ships' routing to mean the recommended notice to be followed when proceeding between predetermined positions.
Traffic Lane	An area within defined limits in which one-way traffic is established. Natural obstacles, including those forming separation zones, may constitute a boundary.
Traffic Separation Scheme	A routing measure aimed at the separation of opposing streams of traffic by appropriate means and by the establishment of traffic lanes.
Train Ferry	A ferry fitted with railway lines to transport railway carriages and wagons across the water.
Training Wall	A mound often of rubble, frequently submerged, built alongside the channel of an estuary or river to direct the tidal stream or current, or both, through the channel so that they may assist in keeping it clear of silt. Termed "jetty" in the USA and Canada.
Transfer of Datum	The method of determining a new chart datum by reference to an established datum whereby the tide will fall to the datum at the new position when it falls to datum at the old one.
Transhipment Area or Lightening Area	Area designated for transfer of cargo from one vessel to another to reduce the draught of the larger vessel. Also known as cargo transfer area.
Transit	Two objects in line are said to be "in transit". See also range.
Transit Port	A port where the cargo handled is merely en route to its destination and is forwarded by coasters, river craft, etc. the port itself is not the final destination before distribution.
Transit Shed	A structure or building on a wharf or quay for the temporary storage of cargo and goods between ship and rail or warehouse, and vice versa. There is a legal difference between a transit shed under the shipowner's control and a warehouse which may not be.
Transporter	A type of travelling crane consisting of a movable bridge or gantry which runs on rails, straddling a cargo (usually coal) dump and projecting over the quay side. A small crane or grab runs along the gantry transporting the cargo from dump to vessel or vice versa.
Transporter Bridge	A type of bridge which may be erected over a waterway consisting of a tower either side of the water connected by a girder system along which a carriage runs. A small platform at road level is suspended from the carriage and on this the road traffic is transported across the waterway.
Trench	Oceanographically, a long characteristically very deep and asymmetrical depression of the sea floor, with relatively steep sides.
Trend of a Coast	The general direction in which it extends.
Triangulation	The measurement of a system of triangles connecting control stations in an area to be surveyed, in order to ascertain the correct relative positions of those stations. Also, the geometrical framework (also called horizontal control) thus obtained.
Trilateration	The measurement of a system of triangles connecting control stations in an area to be surveyed, by measuring the sides of the triangles rather than their angles as in a triangulation.
Trot	A line of system of mooring buoys between which a number of small ships or craft can be secured, head and stern.
Trough	The hollow between two waves. Oceanographically, a long depression of the sea floor characteristically steep-sided and normally shallower, than a trench.
Tufa	A porous concretionary or compact form of calcium carbonate, which is deposited from solution around springs.
Turning Basin	An area of water or enlargement of a channel in a port, where vessels are enabled to turn, and which is kept clear of buoys, etc for that purpose.
Turn-Round	The turn-around of a vessel in a port is the complete operation comprising arrival, discharge and loading of cargo, and departure.
Two-Way Route	A route within defined limits inside which two-way traffic is established, aimed at providing safe passage of ships through waters where navigation is difficult or dangerous.
Uncovered	Exposed; not covered by water.
Under Current	A sub-surface current. See also surface current. There is an implication that the under current is different either in rate or direction from the surface current.
Under Way	Having way. The term, however, is used in the International Regulations for Preventing Collisions at Sea 1972 to mean that a vessel is not at anchor, or made fast to the shore, or aground.
Undercliff	A terrace or lower cliff formed by a landslip.
Undertow	A sub-surface current setting into the deeper water when waves are breaking.
Unexamined	A potential danger to navigation is marked unexamined when the least depth of water over it has not been rigorously determined.
Unwatched Light	A light without any personnel permanently stationed to superintend it.
Upstream	The opposite direction to downstream.
Valley	Oceanographically, a relatively shallow, wide depression, the bottom of which usually slopes continuously downward. the term is generally not used for features that have canyon-like characteristics for a significant portion of their extent.
Veer	The wind is said to veer when it changes direction clockwise.
Vertical Clearance	The height above the datum for heights of the highest part of the underside of the span of a bridge, or the lowest part of an overhead cable. the vertical clearance of fixed bridges is measured from the level of MHWS or MHHW to the underside of the bridge. Formerly termed Headway.
Vertical Datum	A horizontal plane to which heights, depths or levels are referred. See also chart datum, high water datum, Indian Spring Low Water datum, Land Survey datum and Ordnance datum.
Vessel Traffic Service (Vts)	A service implemented by a competent authority to improve the safety and efficiency of vessel traffic and protect the environment. the service shall have the capability to interact with the traffic and respond to traffic situations developing in the VTS area.
Vigia	A reported danger, usually in deep water, whose position is uncertain or whose existence is doubtful. A warning on the chart to denote that undiscovered dangers may exist in the neighbourhood.
Volcanic Ash	Uncemented pyroclastic material consisting of fragments mostly under 4 mm in diameter. Coarse ash in 0·25 to 4 mm in grain size; fine ash is less then 0·25.
Waiting Area	An area with designated limits within which ships must wait for a pilot or representative of the shore authorities.
Warp	A hawser by which a ship can be moved when in harbour, port, etc. the warp is secured to a buoy or some fixed object and brought inboard and hauled upon to move the ship.
Warping Buoy	Mooring buoys specially laid to assist ships hauling off a quay, jetty, etc.
Wash	The accumulation of silt and alluvium in the estuary. Soil carried away by water. Also, the visible and audible motion of agitated water, especially that caused by the passage of a vessel.
Watch Buoy	A buoy placed to mark a special position; in particular, near a light-vessel, to check its position.
Water Boat	A boat (usually self-propelled) fitted with large water tanks and its own pump and hose connections, used in harbours for supplying fresh water to sea-going ships.
Waterborne	Floating; particularly of a ship afloat after being aground, or on being launched.
Watercourse	A natural channel for water, which may sometimes dry.
Waterline	The actual junction of the land and water at any instant. Also, the line along which the surface of the water touches a vessels' hull.
Waterway	A water feature (river, channel, etc.) which can be utilised for communication or transport.
Wave Basin	A device to reduce the size of waves which enter a harbour, consisting of a basin close to the inner entrance to the harbour in which the waves from the outer entrance are absorbed.
Wave Trap	A device used to reduce the size of waves which enter a harbour before they penetrate as far as the quayage. Sometimes it takes the form of diverging breakwaters, and sometimes of small projecting breakwaters situated close within the entrance.
Wave-Cut Shore	A shore or bare rock formed by wave erosion, or on a limestone or other soluble rock by solution. Correctly, a shore which is not a beach is wave-cut.
Way	The motion of a vessel through the water.
Ways	The timber sills upon which a ship is built.
Weather Shore	That from which the wind is blowing.
Weather Side	The side of a vessel towards which, or on the side of a channel from which, the wind is blowing. See also lee side.
Weather Tide	The opposite of lee tide.
Wellhead	The head of the pipe drawing oil from an oilfield or gas from a field of gas.
Wet Dock	A non-tidal basin.
Wharf	A structure similar to a quay alongside which vessels can lie to discharge cargo. Usually constructed of wood, iron or concrete, or a combination of them, and supported on piles. It may be either in continuous contact with the land or offset slightly from it, and may be connected with it by one or more approach piers.
Wharf Crane	Located on a wharf or pier specifically for serving vessels alongside it. Cranes are normally described by their lifting capacity, eg a 15-tonne crane.
Wharfage	In a general way, a charge made against cargo passed on to or over a wharf, quay, or jetty. See also quayage.
Whirlpool	An eddy or vortex of water. Any body of water having a more or less circular motion caused by it flowing in an irregular channel, or by conjunction of opposing currents.
Whistle-Buoy	A buoy which emits a whistle, actuated by compressed air or by the compression of air in a tube by the action of the waves.
Wind Drift Current	A horizontal movement in the upper layers of the sea, caused by wind.
Wind-Rode	An anchored or moored vessel is wind-rode when heading, or riding, into the wind. See also tide-rode.
Wreck	Properly, a vessel that has been wrecked, ie ruined or totally disabled, but the term is confined in hydrography to mean a disabled vessel, either submerged or visible, which is attached to, or foul of, the bottom or cast up on the shore.
Yard	A waterside area constructed and fitted-out for a specific purpose usually indicated by a prefix, eg boat yard, dockyard, shipyard, etc.
Yaw	Unavoidable oscillation of the ship's head either side of the course being steered or when at anchor, due to wind and waves.
Zone Time	The system of time-keeping used by a vessel at sea in which the time kept is that of the appropriate Time Zone.
Zooplankton	The microscopic drifting animal life of the oceans including the larvae of the larger swimming animals and fish.

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