Marine Abbreviation (R to Z)



Reachable on
A charterparty term meaning that the charterer undertakes to provide a loading or discharging berth immediately on the ship’s arrival.
The person or firm named in the contract of carriage to accept the delivery of goods at their destination.
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 conspicuous object
Any object that is readily distinguishable and outstanding on a radar screen on most bearings from seaward.
radar assistance
The communicating to a vessel of navigational information determined by a shore radar, when requested.
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 calling-in point
See reporting point.
radio fog signal
Special transmissions provided by a radiobeacon as an aid to navigation during periods of fog and low visibility.
radio lighthouse
See rotating pattern radiobeacon.
radio station
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.
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. See the relevant Admiralty List of Radio Signals.
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 aero, circular, rotating pattern and directional radiobeacons.
Forms of foraminifera having skeletons of silica.
radiolarian ooze
A siliceous deep-sea ooze formed of the skeletons of radiolaria.
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.
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.
Term used in the USA and Canada for transit (qv).
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.
A comparatively straight part of a river or channel, between two bends.
harbour reach
Reach of a winding river or of an estuary which leads directly to the harbour.
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 a 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 routeing 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, cf 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.
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.
reef island
See coral island.
A device fitted to buoys and beacons to reflect rays of light.
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, cf open waters.
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.
Oceanographically, it has the three following means: A long narrow elevation with steep sides; A long narrow elevation often separating ocean basins, cf rise. The major oceanic mountain system of global extent.
rift valley
See median valley.
ripple marks
Small ridges caused by wave action on sandy or silty shores, and on the seabed. cf backwash marks, beach cusps.
rips: tide
See overfalls.
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, cf canal port, seaport, estuary port.
An open anchorage which may, or may not, be protected by shoals, reefs, etc. Affording less protection than a harbour. Sometimes found outside harbours.
Alternative name for roads.
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.
The angular motion of a ship in the athwartship plane. cf 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.
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.
A routeing 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.
routeing system
Any system of one or more routes or routeing 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.
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 pitching.
The distance a ship has travelled through the water.
the run of the coast. The trend of the coast.
to run down a coast. To sail parallel with it.
to run before the wind. To steer a course downwind.
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.


Safe Port/Berth
“…a port will not be safe unless, in the relevant period of time, the particular ship can reach it, use it and return from it without, in the absence of some abnormal occurrence, being exposed to danger which cannot be avoided by good navigation and seamanship…” Eastern City [1958] 2 Lloyd’s Rep. 127
The longitudinal bending of a ship as the bow and stern are raised whilst the centre is lowered (opposite of hogging).
The amount of salt content expressed by weight in parts of thousands in a liquid.
S&P Broker
Sale and Purchase Broker
Means that Saturdays, Sundays and holidays included will be included in counting the laydays in a charterparty. This presupposes that some hours will be worked on these days.
Single buoy mooring.
Holes throughout the sides of a ship in line with the deck to allow sea water and rain water to be washed overboard.
Sea Cock
The valve by which water can be let into a ship’s interior.
Segregated Ballast Tank
The ballast tank in a tanker which is only allowed to carry ballast water, with no connection to the cargo tanks, in order to avoid pollution. Compulsory in ships built since 1980 by IMO convention.
A merchant who exports goods and who places the contract for the carriage of goods.
The oily waste water containing residues of oil and chemicals arising from cleaning cargo tanks in a tanker.
A space for a container in a tier or between the cell guides on board a contained ship (also called a cell).
The reduction in under keel clearance as she moves from rest through the water.
Radio code signal of extreme distress.
Statement of Facts
A comprehensive narrative and account agreed by the ship’s Master and charterers/consignees or their agents at the end of a stay in port covering dates and times of arrival, of tendering Notice of Readiness, loading and discharging and other details, including hours spent working cargo and other important events.
Straddle Carrier
A lifting vehicle designed for removing containers.
A low part, resembling in shape a saddle, in a ridge or between contiguous seamounts.
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.
Lands in proximity to salt water, which are covered at times by the tide.
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 detached. Some sands partly dry and some are always submerged. cf shifting sand.
(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. cf 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.
of waves. The vertical movement of waves or swell alongside a wharf, jetty, cliff, rocks, etc.
Cellular lava or clinker-like fragments of it.
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.
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.
Almost all waves at sea are caused by wind, though some may be caused by other forces of nature such as volcanic explosions, earthquakes or even icebergs calving. The area where waves are formed by wind is known as the generating area, and Sea is the name given to the waves formed in it. The height of the sea waves depends on how long the wind has been blowing, the fetch, the currents and the wind strength. The Beaufort Wind Scale gives a guide to probable wave heights in the open sea, remote from land, when the wind has been blowing for some time. The effect of sea and swell on ships, and the planning of passages to put sea and swell conditions to best advantage are discussed in Ocean Passages for the World.
sea mile
See mile.
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.
The open water outside the confines of a harbour. Also, a rough sea caused by wind, tide or both.
Alternative name for coastal region.
A long narrow U- or V-shaped shallow depression of the sea floor, usually occurring on a gently sloping fan or plain.
An isolated submarine hill or elevation less prominent than a seamount.
A daymark erected with the express purpose of being visible from a distance to seaward.
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.
A conical seamount.
A port situated on the coast, with unimpeded connection with the sea. cf canal port, estuary port, river port.
See shore.
seasonal changes
(in sea level). Variations in the sea level associated with seasonal changes in wind direction, barometric pressure, rainfall, etc. Marked seasonal changes in weather, such as occur during the monsoons, result in changes in sea level. Where sufficient data are available the changes are given in Admiralty Tide Tables and are taken into account in predictions. In the estuaries of major rivers seasonal changes may also result from changes in level due to melting snow or monsoon rains, which will be more marked than seasonal changes due to winds and barometric pressure.
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.
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.
Intense but minor depressions may have effects of a more localized character. The passage of a line squall, for instance, may set up an oscillation known as a seiche, having a period of anything from a few minutes to an hour or two. The height of the wave may be anything from less than a decimetre to more than a metre in extreme cases. Seiches are usually only apparent as irregularities on the trace of an automatic tide gauge, but large seiches can set up strong, though temporary, currents which may be a danger to small craft.
(stream or tide). Undergoing a complete cycle in half a day.
See scend.
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).
A shoal area in a river, or extending across a river, where the depths are less than those upstream or downstream of it. to shoal. To become more shallow.
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.
A ship is said to take a sheer if, usually due to some external influence, her bows unexpectedly deviate from her course.
See ledge, continental shelf, island shelf.
shelf edge or shelf break
A narrow zone at the outer margin of a shelf along which there is a marked increase of slope.
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.
A descriptive term for gravel (qv).
ship canal
A canal large enough to permit the passage of ocean-going vessels.
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 safety fairway
Area designated as a fairway by USA within which no artificial island or fixed structure, whether temporary or permanent is permitted.
ship’s head or heading
The direction in which a ship is pointing at any moment.
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.
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. cf bank, shallow. Oceanographically, an offshore hazard to surface navigation composed of unconsolidated material.
The meeting of sea and land considered as a boundary of the sea. cf coast. Interchangeable with coast when used in a wide sense to denote land bordering the sea as seen from a vessel, cf foreshore. Also, a prop fixed under the ship’s bottom or at her side, to support her in dry dock.
to shore up. To support by means of shores round a vessel.
Another name for coastline (qv), in a more general sense.
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.
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. cf clay. to silt. To choke or be choked by silt.
Single Anchor Leg Mooring (SALM)
Consists of a rigid frame or tube with a buoyancy device at its upper end, secured at its lower end to a universal joint on a large steel or concrete base resting on the seabed, and at its upper end to a mooring buoy by a chain or wire span. Oil flows into the frame through the universal joint at its lower end and out of the frame through a cargo hose connected to a fluid swivel-assembly at its upper end. When the pull of a vessel is taken by the mooring buoy, the frame inclines towards the vessel and the buoy may dip. When the vessel swings to wind or stream, the frame swings with her on the articulated joint at its foot. This type of mooring is particularly suited to loading from deep water sub-sea wellheads.
Single Anchor Leg Storage (SALS)
Consists of a SALM type of mooring system that is permanently attached to the stem or stern of a storage vessel through a yoke supported by a buoyancy tank. Tankers secure to the storage vessel to load.
A rocky islet.
slack water
That period of negligible horizontal water movement when a rectilinear tidal stream is changing direction.
An accumulation of mud or ooze on the bed of a river, channel or harbour. Also, such an accumulation left exposed by the tide.
A local calm streak on the water caused by oil. Also, the calm patch left by the quarter of a ship when turning sharply.
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.
A small feature on the seabed capable of damaging nets and other fishing gear. Also called a fastener.
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.
A passage between two sea areas. A passage having an outlet at either end. Also, an arm of the sea or large inlet.
Measured or charted depth of water or the measurement of such a depth. cf reduction of soundings.
To sound. To determine the depth of water.
A buoy in the form of a pole which is moored to float nearly vertical.
The speed of a vessel refers to her speed through the water unless otherwise specified. cf ground speed.
spending beach
The beach in a wave basin (qv) 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.
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.
A long narrow shoal (if submerged) or a tongue of land (if above water), extending from the shore and formed of any material.
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.
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.
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, cf 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
See mile.
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.
The graduations of shade or colour produced on a chart by means of dots.
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.
A comparatively narrow passage connecting two seas or two large bodies of water.
Oceanographicaliy, 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.
A feature is said to be submerged if it has sunk under water, or has been covered over with water.
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.
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. Main circulations. The general surface current circulation of the world is shown on the World Climatic Charts in Ocean Passages for the World (NP136) and in the various volumes of Admiralty Sailing Directions. The main cause of surface currents in the open ocean is the direct action of the wind on the sea surface and a close correlation accordingly exists between their directions and those of the prevailing winds. Winds of high constancy blowing over extensive areas of ocean will naturally have a greater effect in producing a current than will variable or local winds. Thus the North-east and South-east Trade Winds of the two hemispheres are the main spring of the mid-latitude surface current circulation. In the Atlantic and Pacific Oceans the two Trade Winds drive an immense body of water W over a width of some 50° of latitude, broken only by the narrow belt of the E-going Equatorial Counter-current, which is found a few degrees N of the equator in both these oceans. A similar transport of water to the W occurs in the South Indian Ocean driven by the action of the South-east Trade Wind. The Trade Winds in both hemispheres are balanced in the higher latitudes by wide belts of variable W winds. These produce corresponding belts of predominantly E-going sets in the temperate latitudes of each hemisphere. With these E-going and W-going sets constituting the N and S limbs, there thus arise great continuous circulations of water in each of the major oceans. These cells are centred in about 30°N and S, and extend from about the 10th to at least the 50th parallel in both hemispheres. The direction of the current circulation is clockwise in the N hemisphere and counter-clockwise in the S hemisphere.
The difference in height between predicted and observed tides due to abnormal weather conditions. See Admiralty Tide Tables. cf positive surge, negative surge, storm surge. 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.
Strong winds blowing steadily over the sea set up a surface current which raises sea level in the direction in which the wind is blowing, and lowers sea level in the opposite direction. Tidal predictions are computed for average conditions, including average barometric pressure. Sea level is lowered by high, and raised by low barometric pressure. A change of 34 millibars in the heights of the barometer can cause a change in sea level of 0.3 m but the effect of a change in pressure may not be felt immediately and may, in fact, not be experienced until after the cause of the change has disappeared. Since depressions are frequently accompanied by strong winds, a resulting change in sea level is often due to a combination of the effects of both wind and pressure. Such changes in sea level are superimposed on the normal tidal cycles obtained by predictions, and can be regarded as a temporary change in MSL. A rise in sea level is sometimes known as a positive surge and a fail as a negative surge. Reduced tidal levels may also be experienced in settled weather, a persisting area of high pressure may reduce tidal levels by 0.3 m or more for several days. Both positive and negative surges may appreciably alter the time of high and low water from that predicted. This effect is greater where the tidal range is small. Variations from the predicted time of as much as an hour are not uncommon and in 1989 a high water at Lowestoft was delayed by over 3 hours.
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.
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, cf gut.
Commonly used contraction of drag sweep (qv).
Swell is the wave motion caused by a meteorological disturbance, which persists after the disturbance has died down or moved away. Swell often travels for considerable distances out of its generating area, maintaining a constant direction as long as it keeps in deep water. As the swell travels away from its generating area, its height decreases though its length and speed remain constant, giving rise to the long low regular undulations so characteristic of swell. The measurement of swell is no easy task. Two or even three swells from different generating areas, are often present and these may be partially obscured by the sea waves also present. For this reason a confused swell is often reported. Some climatic atlases give world-wide monthly distribution of swell, but for the reasons given above and the small number of observations in some oceans they should be used with caution.
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.


Twenty foot equivalent unit. Standard of measurement used in container transport for expressing the volume of trade, the capacity of container ships. It is based on dimensions of a cargo container 20 ft long x 8 ft wide x 6ft 6″ high, maximum load approximately 9 tons.
Time Charterparty
An agreement under which the shipowner puts his vessel at the disposal of the charterer for a period of time, during which the charterer pays hire. The period may also be expressed by reference to a particular voyage (a trip time charter). The charterer carries the risk of delays on passage (e.g. as the result of bad weather).
A quick action fastener used to secure a container to a deck or hatch cover or to another container in the stack.
A knoll having a comparatively smooth, flat top with minor irregularities.
An extensive elevated region with a flat-topped level surface.
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. cf cable buoy.
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.
Concrete masses the size of boulders, cast with four stump-legs so that the masses interlock. Used for the pitching of breakwaters and seawalls.
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
See basin.
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.
tidal gauge
An instrument which registers the height of the tide against a scale.
automatic tide gauge. An instrument which measures and records the tidal data.
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.
A graduated vertical staff used for measuring the height of the tide.
Pools worn in seashore rocks, left full of water when the tide level has fallen below them.
tide race
See race.
tide-raising forces
The forces exerted by the Sun and Moon which cause the tides.
See overfalls.
An anchored or moored ship is tide-rode when heading into the tidal stream. cf wind-rode.
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.
timber pound
See pound.
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. cf Standard Time, Date Line.
A long, narrow and usually low, salient point of land. cf spit.
An identification shape, fitted on the tops of beacons and buoys, cf daymark.
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.
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 (qv). Also used in ships’ routeing to mean the recommended notice to be followed when proceeding between predetermined positions.
tractive forces
See tide-raising forces.
traffic flow
established direction of traffic flow. A traffic flow pattern indicating the directional movement of traffic as established within a Traffic Separation Scheme.
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.
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 routeing 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.
Two objects in line are said to be ‘in transit’. cf 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.
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.
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.
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.
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.
A line of system of mooring buoys between which a number of small ships or craft can be secured, head and stern.
The hollow between two waves. Oceanographically, a long depression of the sea floor characteristically steep-sided and normally shallower, than a trench.
A porous concretionary or compact form of calcium carbonate, which is deposited from solution around springs.
turning basin
See basin.
The turn-around of a vessel in a port is the complete operation comprising arrival, discharge and loading of cargo, and departure.
twenty-foot equivalent unit
See container.
See astronomical, nautical and civil twilight.
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.


Free space left in filling a liquid oil cargo tank to allow for expansion when the cargo is heated for pumping.
Exposed; not covered by water.
under current
A sub-surface current, cf 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.
A terrace or lower cliff formed by a landslip.
A sub-surface current setting into the deeper water when waves are breaking.
See below-water.
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.
The opposite direction to downstream (qv).


Vessel Traffic Information System.
Voyage Charterparty
An agreement under which a shipowner agrees to carry a specified cargo from a berth or port to its destination, in return for which the charterers pay freight. Time for loading and discharging is usually specified (see Laytime). The risk of delays on passage is carried by the shipowner.
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.
See magnetic variation.
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 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. cf safe overhead clearance.
vertical datum
A horizontal plane to which heights, depths or levels are referred. See 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.
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.


A document used in the carriage of goods which acts as a consignment note and receipt for shipping with full descriptions and terms of carriage. Similar to a bill of lading, except that it is not a document of title, and therefore it is not negotiable.
Whether Cleared At Customs House Or Not.
Whether Cleared Customs Or Not.
Weather Working Day
Wear and Tear
Normal deterioration of an article or a working part during the course of its use or through age.
Whether in Berth or Not
Whether in Port or Not
Wing Tank
A space used for loose bulk or liquid cargo, ballast water at either side of a vessel’s main cargo compartments.
waiting area
An area with designated limits within which ships must wait for a pilot or representative of the shore authorities.
See catwalk.
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.
to warp. To move a ship from one place to another by means of a warp.
warping buoy. Mooring buoys specially laid to assist ships hauling off a quay, jetty, etc.
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.
water track
See track.
Floating; particularly of a ship afloat after being aground, or on being launched.
A natural channel for water, which may sometimes dry.
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.
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 take 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.
The motion of a vessel through the water.
The timber sills upon which a ship is built.
way point
See reporting point.
weather side
The side of a vessel towards which, or on the side of a channel from which, the wind is blowing. cf lee side.
weather shore
That from which the wind is blowing.
weather tide
The opposite of lee tide (qv).
The head of the pipe drawing oil from an oilfield or gas from a field of gas.
wet dock
A non-tidal basin.
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.
In a general way, a charge made against cargo passed on to or over a wharf, quay, or jetty. cf quayage.
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.
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.
white horses
See breakers.
wind drift current
A horizontal movement in the upper layers of the sea, caused by wind.
An anchored or moored vessel is wind-rode when heading, or riding, into the wind, cf tide-rode.
wire drag
See drag sweep.
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.


York-Antwerp Rules
Uniform set of rules which define general average.
A waterside area constructed and fitted-out for a specific purpose usually indicated by a prefix, eg boat yard, dockyard, shipyard, etc.
yard craft
See craft.
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 (qv).
The microscopic drifting animal life of the oceans including the larvae of the larger swimming animals and fish.
The point in the heavens directly above the observer.

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