Nautical Terms: The Complete A–Z Glossary
Nautical terms are the specialised words used aboard ship to describe a vessel's parts, its position and direction, how it moves, how it is navigated, and how it is worked safely.
Edward Caine26 min read
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Nautical Terms: The Complete A–Z Glossary
Nautical terms are the specialised words used aboard ship to describe a vessel’s parts, its position and direction, how it moves, how it is navigated, and how it is worked safely. This glossary defines more than 326 maritime terms in plain English.
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A (22 TERMS)
Abeam#
At right angles to the fore-and-aft line of the ship; on the beam.
Able Seaman (AB)#
A certificated deck rating competent in steering, lookout, mooring and general seamanship.
Aft#
Towards or at the stern of the ship.
Aground#
Resting on the bottom; a vessel that has run onto the seabed.
AIS (Automatic Identification System)#
A transponder system that broadcasts a vessel’s identity, position, course and speed to other ships and shore stations.
All-Round Light#
A navigation light showing an unbroken beam over the full 360 degrees of the horizon.
Almanac (Nautical Almanac)#
A yearly publication tabulating the positions of the sun, moon, planets and stars for celestial navigation.
Amidships#
The middle of the ship along its length; also the order to centre the rudder.
Amplitude#
The angular distance of a celestial body north or south of east or west at rising or setting, used to check compass error.
Anchor Watch#
A watch kept at anchor to ensure the anchor is holding and the ship is not dragging.
Anderson Turn#
A rapid single-turn manoeuvre to return to a person overboard, best used with good manoeuvrability and the casualty in sight.
Angle of Loll#
The angle a ship with negative initial stability settles to, heeled over rather than upright.
Anti-Grounding Alarm#
The ECDIS function that warns when the planned route or the ship’s track crosses the safety contour or a charted danger.
Anticyclone#
A region of high atmospheric pressure, usually bringing settled, fair weather.
Apparent Wind#
The wind felt aboard a moving vessel — the vector sum of the true wind and the ship’s own motion.
Appraisal#
The first stage of passage planning: gathering and reviewing all information relevant to the voyage before any plan is drawn.
Astern#
Behind the ship; also the movement of a vessel going backwards.
Athwartships#
Across the ship, at right angles to the fore-and-aft line.
Azimuth#
The horizontal direction of a celestial body expressed as a true bearing.
B (25 TERMS)
Backing#
An anticlockwise change in wind direction; the opposite of veering.
Ballast#
Weight, usually seawater in tanks, carried to improve stability, trim or draught.
Bar#
A shoal of sand or mud across a harbour mouth or river entrance.
Bareboat Charter#
Hiring the ship alone, without crew or management; the charterer operates it as if the owner.
Beam#
The breadth of a vessel at its widest point; also a direction at right angles to the keel.
Bearing#
The horizontal direction of one object from another, expressed in degrees from north.
Beaufort Scale#
A scale relating wind force from 0 to 12 to observed sea and land conditions.
Bend#
A knot used to join two ropes together.
Berth#
A place where a ship is moored or anchored; also a crew member’s bunk.
Bight#
A loop or the slack middle part of a rope between its ends.
Bilge#
The turn of the hull where the bottom meets the side; also the lowest internal space where water collects.
Bill of Lading#
The document that receipts cargo, evidences the contract of carriage, and serves as a document of title to the goods.
Block Coefficient#
The ratio of a hull’s underwater volume to the enclosing box; a measure of how full or fine the hull is.
Bollard#
A strong post on a quay or deck to which mooring lines are made fast.
Bosun#
The senior deck rating, who supervises the deck crew and routine maintenance.
Bow#
The forward part of a vessel.
Bowline#
A knot forming a secure fixed loop that does not slip or jam.
Breathing Apparatus#
Self-contained equipment supplying clean air for entry into smoke-filled or oxygen-deficient spaces.
Bridge#
The compartment from which a ship is navigated and controlled.
Bridge Resource Management (BRM)#
The coordinated use of all bridge personnel, equipment and information for safe navigation.
Bulkhead#
A vertical partition within a ship, often watertight, dividing it into compartments.
Bulwark#
The solid plating carried up around the edge of the weather deck as a barrier against the sea.
Bunkers / Bunkering#
A ship’s fuel oil; bunkering is the operation of taking fuel aboard.
Buoyage#
A system of floating marks indicating channels and dangers; the IALA system defines lateral and cardinal marks.
C (29 TERMS)
Cadet#
A trainee officer accumulating sea time and study towards a certificate of competency.
Camber#
The athwartships curvature of a deck that sheds water to the sides.
Capstan#
A vertical rotating drum used for heaving on mooring ropes or cable.
Cardinal Mark#
An IALA buoy showing the direction of safe water relative to a danger, named for the cardinal point on which it lies.
Cargo Plan#
A diagram showing the distribution and stowage of cargo throughout the ship.
Centre of Buoyancy#
The centroid of the underwater volume, through which the force of buoyancy acts.
Centre of Gravity#
The point through which the entire weight of the ship acts.
Certificate of Competency (CoC)#
The licence issued under STCW certifying an officer’s rank and qualifications.
Chafe#
Wear on a rope or line caused by rubbing against a hard surface.
Chart Correction#
The updating of a chart from Notices to Mariners to keep it current and safe to use.
Chart Datum#
The reference level to which charted depths and drying heights are measured, usually Lowest Astronomical Tide.
Charted Depth#
The depth of water below chart datum printed on the chart at a given position.
Charter Party#
The contract under which a shipowner hires out a vessel to a charterer.
Chief Officer#
The head of the deck department and second in command, responsible for cargo, stability and deck maintenance.
Class of Fire#
The classification of fires by fuel type (A solids, B liquids, C gases, D metals, F cooking oils), which determines the correct extinguisher.
Classification Society#
An organisation that sets and verifies standards for the construction and maintenance of ships.
Cleat#
A horned fitting around which a rope is belayed to secure it.
Cocked Hat#
The small triangle formed when three position lines fail to meet at a point, indicating observational error.
Cofferdam#
A narrow void space separating two compartments to prevent leakage of liquids between them.
Cold Front#
The leading edge of advancing cold air that undercuts warmer air, often bringing squalls and a wind shift.
COLREGs#
The International Regulations for Preventing Collisions at Sea, 1972 — the rules of conduct, lights, shapes and signals between vessels. Read the full COLREGs guide ›
Compass Error#
The combined effect of variation and deviation; the angle between compass north and true north.
Compass Rose#
The graduated circle printed on a chart showing true and magnetic directions.
Conning#
The act of directing the steering of a ship through helm and engine orders.
Constrained by Draught#
A power-driven vessel severely restricted in her ability to deviate from course because of her draught relative to the depth.
Course#
The intended horizontal direction of travel, measured in degrees.
Course Made Good#
The actual track achieved over the ground after the effects of tide and leeway.
CPA / TCPA#
Closest Point of Approach and Time to CPA — the predicted nearest passing distance to a target and the time until it occurs.
Crossing Situation#
Where two power-driven vessels cross with risk of collision; the vessel with the other on her starboard side gives way.
D (22 TERMS)
Datum#
A reference level or surface for measurement — vertical for depths and heights, horizontal for position.
Davit#
The crane-like device used to swing out, lower and recover a lifeboat or rescue boat.
Day Shapes#
Black shapes — ball, cone, cylinder or diamond — shown by day to signal a vessel’s status under the COLREGs.
Dead Reckoning#
Estimating position from a known fix using only the course steered and distance run, without external references.
Deadweight#
The total weight a ship can carry — cargo, fuel, stores, crew and water — at her load line.
Demurrage#
Money paid to the shipowner when loading or discharging exceeds the agreed laytime.
Departure#
The east-west distance made good between two positions, used in plane sailing.
Depression#
A region of low atmospheric pressure bringing wind, cloud and unsettled weather.
Despatch#
Money paid by the owner to the charterer for completing cargo work sooner than the agreed laytime.
Deviation#
The compass error caused by the ship’s own magnetic field, varying with the ship’s heading.
DGPS#
Differential GPS — satellite positioning improved by correction signals from shore reference stations.
Displacement#
The weight of water displaced by a floating ship, equal to the ship’s own total weight.
Distress#
A situation of grave and imminent danger requiring immediate assistance.
Double Bottom#
The space between the inner and outer bottom plating, used for ballast, fuel or fresh water.
Doubling the Angle on the Bow#
Finding distance off by running between two relative bearings, the second twice the first; the run equals the distance off.
Draught (Draft)#
The vertical distance from the waterline to the lowest point of the hull — how deep the ship sits.
Draught Survey#
Determining the weight of bulk cargo loaded or discharged by measuring the ship’s change in draught.
Drill#
A practised rehearsal of an emergency procedure such as fire, abandon ship or man overboard.
Drogue#
A device streamed from a vessel to slow her or to hold her head to the sea.
Drying Height#
The height a feature dries above chart datum, shown underlined on the chart; covered only when the tide exceeds it.
DSC (Digital Selective Calling)#
The GMDSS method of sending automated distress, urgency and routine alerts.
Dunnage#
Material laid under and between cargo to protect it and assist drainage, ventilation and securing.
E (10 TERMS)
Ebb#
The falling tide, when the tidal stream runs seaward.
ECDIS#
Electronic Chart Display and Information System — a type-approved navigation system using official electronic charts. Read the full ECDIS guide ›
Echo Sounder#
An instrument that measures water depth by timing an acoustic pulse to the seabed and back.
Embarkation Ladder#
The ladder rigged at the muster station by which crew board the survival craft.
Enclosed Space#
A space with limited openings, poor ventilation and a possible dangerous atmosphere, entered only under permit.
EP (Estimated Position)#
A dead-reckoning position corrected for the estimated effect of tide and leeway.
EPIRB#
Emergency Position-Indicating Radio Beacon — a device that transmits a distress alert and position via satellite.
ETA#
Estimated Time of Arrival at a destination or waypoint.
Eye Splice#
A permanent loop worked into the end of a rope by tucking its strands back into the standing part.
F (14 TERMS)
Fairlead#
A fitting that guides a mooring line in the required direction and reduces chafe.
Fathom#
A unit of depth equal to six feet (1.83 m), used on older charts.
Fender#
A cushion hung over the ship’s side to protect the hull when alongside.
Fetch#
The distance of open water over which the wind blows to build up waves.
Fire Triangle#
The three elements — heat, fuel and oxygen — that must combine for combustion to occur.
Fix#
A position established from external references — bearings, ranges or GNSS — at a known time.
Fixed Fire-Fighting System#
A permanently installed system such as CO2, foam or water mist that protects a particular space.
Flag State#
The country in which a ship is registered and whose laws and regulations she must follow.
Flood#
The rising tide, when the tidal stream runs landward.
Following Sea#
A sea running in the same direction as the ship’s heading.
Forecastle#
The forward part of the upper deck; historically the crew’s quarters.
Frame#
A transverse rib of the hull structure to which the shell plating is attached.
Free Surface Effect#
The loss of stability caused by liquid moving freely in a slack tank, which raises the effective centre of gravity.
Freeboard#
The vertical distance from the waterline to the freeboard deck — the reserve buoyancy above the water.
G (11 TERMS)
Gangway#
The opening or ramp by which people board or leave a ship.
Gas-Free#
The condition of a space certified clear of dangerous gas concentrations before entry or hot work.
Give-Way Vessel#
Under COLREGs, the vessel required to keep clear and take early, substantial action to avoid the other.
GM (Metacentric Height)#
The vertical distance between a ship’s centre of gravity and its metacentre — the measure of initial stability.
GMDSS#
Global Maritime Distress and Safety System — the international framework for distress alerting and communications.
Gnomonic Chart#
A chart projection on which a great circle appears as a straight line, used for great-circle route planning.
GNSS#
Global Navigation Satellite System — the umbrella term covering GPS, GLONASS and Galileo.
Great Circle#
The shortest route between two points on the globe, lying on a circle centred on the earth’s centre.
Gybe#
To turn a sailing vessel’s stern through the wind.
Gyrocompass#
A compass using a spinning gyroscope to indicate true north, unaffected by magnetism.
GZ (Righting Lever)#
The horizontal distance between the lines of weight and buoyancy at a given heel — the lever that rights the ship.
H (15 TERMS)
Hand Bearing Compass#
A portable compass used to take bearings of objects for position fixing.
Handover#
The formal transfer of responsibility and essential information from one watchkeeper to the next.
HAT (Highest Astronomical Tide)#
The highest tide level predicted under average conditions; the datum for charted vertical clearances.
Hawse#
The part of the bow where the anchor cables run out through the hawsepipe.
Head-On Situation#
Where two power-driven vessels meet on or near reciprocal courses; each alters course to starboard.
Heading#
The direction in which a ship’s bow is pointing at a given moment.
Heave To#
To hold a vessel nearly stationary in heavy weather by balancing engine, helm and sea.
Heaving Line#
A light weighted line thrown ashore to haul a heavier mooring rope across.
Heel#
The transverse inclination of a ship caused by an external force such as wind or turning.
Height of Tide#
The height of the sea surface above chart datum at a given moment; added to charted depth to find actual depth.
Helm#
The wheel or tiller by which a ship is steered; also the order to apply rudder.
Hitch#
A knot used to secure a rope to a spar, ring or other object.
Hogging#
A hull strain in which the middle is better supported than the ends, making the ends droop.
Hull#
The main watertight body of a ship.
Hydrostatic Release Unit#
A device that automatically frees a liferaft and lets it float clear if the ship sinks.
I (8 TERMS)
IALA#
The body that defines the international buoyage system of lateral and cardinal marks.
Immersion Suit#
An insulated, waterproof suit that protects a survivor against hypothermia in cold water.
IMO#
The International Maritime Organization — the UN agency regulating shipping safety, security and pollution.
Inclining Experiment#
A test in which known weights are shifted to determine a ship’s lightship centre of gravity.
Intercept#
In celestial navigation, the difference between calculated and observed altitude, plotted to give a position line.
ISM Code#
The International Safety Management Code — requiring a documented safety management system aboard and ashore.
Isobar#
A line on a weather chart joining points of equal atmospheric pressure.
ISPS Code#
The International Ship and Port Facility Security Code, setting maritime security requirements.
J (2 TERMS)
K (3 TERMS)
L (21 TERMS)
Lashing#
Rope, wire or webbing used to secure cargo or equipment against movement.
LAT (Lowest Astronomical Tide)#
The lowest tide level predicted under average meteorological conditions; the usual chart datum.
Lateral Mark#
An IALA buoy marking the side of a channel — port or starboard — to be left on a given hand.
Latitude#
Angular distance north or south of the equator, measured in degrees.
Laytime#
The time allowed to the charterer for loading and discharging cargo before demurrage is incurred.
Leading Lights#
Two lights or marks in line giving a safe approach bearing into harbour.
Lee#
The side or direction sheltered from the wind; the opposite of windward.
Lee Shore#
A shore onto which the wind is blowing, hazardous to a vessel that could be driven onto it.
Leeway#
The sideways drift of a vessel caused by wind — the angle between the heading and the course made good.
Lifeboat#
An enclosed or open survival craft for evacuating a ship in emergency.
Lifebuoy#
A ring-shaped buoyant device thrown to a person who has fallen into the water.
Lifejacket#
A buoyant garment that supports a person afloat and turns an unconscious wearer face-up.
Liferaft#
An inflatable survival craft stowed in a canister and launched when abandoning ship.
Lightship#
The weight of the ship complete and ready for sea but without cargo, fuel, stores or crew.
List#
A persistent transverse inclination caused by an internal imbalance such as off-centre weight or flooding.
Load Line#
The mark on a ship’s side showing the maximum permitted draught for a zone and season; the Plimsoll mark.
Log#
An instrument measuring a ship’s speed and distance through the water; also the official record book.
Longitude#
Angular distance east or west of the prime meridian, measured in degrees.
Lookout#
The duty, required at all times by COLREGs Rule 5, of watching and listening by all available means to assess risk.
Loom#
The glow of a light reflected in sky or haze, seen before the light itself rises above the horizon.
LSA (Life-Saving Appliances)#
The survival craft, rescue boats and equipment required by SOLAS.
M (20 TERMS)
Magnetic North#
The direction indicated by a magnetic compass, differing from true north by the variation.
Man Overboard (MOB)#
The emergency in which a person falls from the ship into the water. Read the full MOB procedure ›
Manifest#
The complete list of all cargo carried on a voyage.
Marlinspike#
A pointed tool used to open the strands of a rope when splicing.
MARPOL#
The International Convention for the Prevention of Pollution from Ships.
Master#
The officer in command of the ship, holding overall authority and responsibility for her and all aboard.
Masthead Light#
A white light shown forward over the centreline, visible ahead, carried by power-driven vessels under way.
Mate’s Receipt#
A document acknowledging that cargo has been received aboard, later exchanged for the Bill of Lading.
Mayday#
The spoken radio distress signal indicating grave and imminent danger requiring immediate assistance.
Mean High Water Springs#
The average high-water level at spring tides; the datum for charted heights of land and structures.
Mercator Projection#
A chart projection on which rhumb lines are straight and angles are preserved — the standard for navigation.
Meridian#
A great circle passing through both poles; a line of longitude.
Meridian Passage#
The instant a celestial body crosses the observer’s meridian, used to find latitude.
Metacentre#
The point about which a ship’s buoyancy force effectively acts as she heels through small angles.
MLC (Maritime Labour Convention)#
The convention setting minimum standards for seafarers’ employment, hours and welfare.
MMSI#
Maritime Mobile Service Identity — the unique nine-digit number identifying a vessel in DSC and AIS.
Mooring#
Securing a vessel to a berth, buoy or anchor; also the lines and equipment used.
Mooring Line#
A rope or wire securing a ship to a berth — head line, breast line, spring or stern line.
Muster List#
The station bill assigning every crew member their duties and stations for fire, abandon ship and man-overboard emergencies.
Muster Station#
The designated assembly point where crew and passengers gather in an emergency.
N (8 TERMS)
Narrow Channel#
A channel in which COLREGs Rule 9 requires vessels to keep to the starboard side of the fairway.
Nautical Mile#
A unit of distance of 1,852 metres, equal to one minute of latitude.
Neap Tide#
The tide of least range, occurring near the first and last quarters of the moon.
Night Orders#
The master’s written instructions to watchkeepers for the navigation and safety of the coming night.
No-Go Area#
An area marked on the passage plan that the vessel must not enter because the water is too shallow or dangerous.
Not Under Command (NUC)#
A vessel that, through exceptional circumstance, cannot manoeuvre as the rules require and so cannot keep out of the way.
Notice of Readiness (NOR)#
The formal notice that a ship has arrived and is ready to load or discharge, which starts laytime running.
Notices to Mariners#
Official notices issued to correct charts and publications and to warn of changes affecting safe navigation.
O (3 TERMS)
OOW (Officer of the Watch)#
The officer responsible for the safe navigation and operation of the ship during a watch.
Overfalls#
Turbulent, breaking water caused by a strong tidal stream over an uneven seabed or against the wind.
Overtaking#
Approaching another vessel from more than 22.5 degrees abaft her beam; the overtaking vessel must keep clear.
P (17 TERMS)
Painter#
A rope at the bow of a boat by which it is made fast or towed.
Parallel Indexing#
A radar technique for monitoring a vessel’s track relative to a fixed object along a pre-set line.
Passage Plan#
The berth-to-berth plan covering the four stages: appraisal, planning, execution and monitoring.
Pelorus#
A sighting instrument, or dumb compass, used to take relative bearings.
Permit to Work#
A formal documented system that controls high-risk tasks such as enclosed-space entry and hot work.
Pilot#
A mariner with local knowledge who advises on the navigation of a ship in confined waters.
Pilotage#
Navigation in confined or coastal waters by reference to visual marks and local knowledge.
Pitch#
The fore-and-aft rotational motion of a ship in a seaway; also the advance of a propeller per revolution.
Plane Sailing#
Calculating course and distance by treating the earth’s surface as flat over short distances.
Plimsoll Mark#
The load line marked on a ship’s side indicating the maximum legal draught.
Polaris (Pole Star)#
The star lying close to the north celestial pole, used to find latitude and check compass error.
Port#
The left-hand side of a ship when facing forward.
Port State Control (PSC)#
The inspection of foreign ships in national ports to verify compliance with international conventions.
Position Line#
A line on the chart somewhere along which the ship is known to lie, from a bearing, range or transit.
PPE (Personal Protective Equipment)#
Gear such as helmet, gloves, goggles and safety boots worn to reduce injury.
Prime Meridian#
The zero meridian of longitude, passing through Greenwich.
Pyrotechnics#
Distress signals such as rocket parachute flares, hand flares and buoyant smoke signals.
Q (1 TERM)
Quarter#
The part of a ship’s side towards the stern, between the beam and the stern.
R (16 TERMS)
RACON#
A radar beacon that, when triggered by a ship’s radar, paints an identifying coded mark on the screen.
Radar#
A system using radio waves to detect the range and bearing of other vessels and objects.
Range#
The distance to an object; also the difference in height between successive high and low waters.
Range of Stability#
The span of heel angles over which a ship retains a positive righting lever.
Reciprocal#
The opposite direction to a given bearing or course, 180 degrees away.
Relative Bearing#
The direction of an object measured relative to the ship’s head rather than to north.
Reserve Buoyancy#
The watertight volume above the waterline that gives extra buoyancy if the ship is further immersed.
Restricted in Ability to Manoeuvre (RAM)#
A vessel restricted by the nature of her work from keeping out of the way of others.
Restricted Visibility#
Any condition such as fog, mist or heavy rain that reduces visibility and brings COLREGs Rule 19 into force.
Rhumb Line#
A line crossing all meridians at the same angle; a constant-course track on a Mercator chart.
Righting Moment#
The moment that returns a heeled ship upright — displacement multiplied by the righting lever GZ.
Risk Assessment#
The systematic identification of hazards and evaluation of controls before a task is begun.
Risk of Collision#
Deemed to exist if the compass bearing of an approaching vessel does not change appreciably.
Roll#
The transverse rotational motion of a ship from side to side in a seaway.
Rudder#
The hinged underwater foil at the stern used to steer the ship.
Running Fix#
A position obtained by transferring an earlier position line to cross a later one, allowing for the run between.
S (39 TERMS)
Safe Speed#
A speed at which a vessel can take proper action to avoid collision and stop within a distance suited to the conditions.
Safety Contour#
The depth contour set in ECDIS that separates safe from unsafe water for the vessel; it drives the anti-grounding alarms.
Sagging#
A hull strain in which the ends are better supported than the middle, making the middle droop.
Sailing Directions#
Admiralty pilot books describing coasts, ports, tides and navigational features in detail.
SART#
Search and Rescue Transponder — a device that marks a survival craft’s position on a rescuer’s radar.
Scharnow Turn#
A recovery turn used when the point to be returned to is well astern and time has passed since the casualty was lost.
Scope#
The ratio of anchor cable paid out to the depth of water; greater scope improves holding.
Sea Anchor#
A drogue streamed from the bow to hold a vessel head to sea and reduce drift in heavy weather.
Sea State#
A description of wave height and character, commonly graded on a scale of 0 to 9.
Sea Time#
Qualifying service performed at sea that counts towards a certificate of competency.
Set and Drift#
The direction (set) and rate (drift) of a tidal stream or current acting on the ship.
Sextant#
An instrument measuring the angle between two objects, used for celestial position fixing.
Sheer#
The fore-and-aft curvature of a ship’s deck line, rising towards bow and stern.
Shell Plating#
The outer watertight plating that forms the skin of the hull.
Shroud#
A standing-rigging wire supporting a mast athwartships.
Sidelights#
The red port and green starboard lights that show the aspect of a vessel to others at night.
Slack Water#
The brief period of little or no tidal stream around the turn of the tide.
SOLAS#
The International Convention for the Safety of Life at Sea — the principal treaty on ship safety, construction and equipment.
Sound Signals#
Prescribed whistle signals indicating a vessel’s manoeuvres or her presence in restricted visibility.
Sounding#
A measured depth of water referenced to chart datum; also the act of measuring depth.
Splice#
To join or finish a rope permanently by interweaving its strands.
Spring (Mooring)#
A mooring line led forward or aft to stop the ship ranging along the berth.
Spring Tide#
The tide of greatest range, occurring near new and full moon.
Squall#
A sudden, sharp increase in wind, often with rain and a shift in direction.
Squat#
The bodily sinkage and change of trim a ship undergoes in shallow water, reducing under-keel clearance.
Stability#
A ship’s tendency to return upright after being heeled by an external force.
Stand-On Vessel#
Under COLREGs, the vessel required to keep her course and speed while the give-way vessel takes avoiding action.
Standing Orders#
The master’s permanent written instructions on how the ship is to be run and when the master is to be called.
Starboard#
The right-hand side of a ship when facing forward.
Stay#
A standing-rigging wire supporting a mast in the fore-and-aft direction.
STCW#
The Standards of Training, Certification and Watchkeeping for Seafarers.
Stem#
The foremost structural member of the bow.
Stern#
The aftermost part of a vessel.
Sternlight#
A white light shown at the stern and visible from astern.
Stiff and Tender#
A ship with a large GM is stiff and rolls quickly; one with a small GM is tender and rolls slowly.
Stowage Factor#
The volume a unit weight of cargo occupies, used to plan how a cargo will fit aboard.
Survival Craft#
A craft capable of sustaining the lives of survivors after abandonment, such as a lifeboat or liferaft.
Swell#
Long, regular waves that have travelled out of the area in which they were generated.
Synoptic Chart#
A weather chart showing the pattern of pressure systems and fronts at a given time.
T (15 TERMS)
Tack#
To turn a sailing vessel’s bow through the wind; also the lower forward corner of a sail.
Thermal Protective Aid#
A bag or suit that reduces a survivor’s loss of body heat by convection and evaporation.
Tidal Diamond#
A lettered symbol on a chart keyed to a table of tidal stream directions and rates.
Tidal Stream#
The horizontal movement of water caused by the rise and fall of the tide.
Tide#
The periodic rise and fall of the sea caused by the gravitational pull of the moon and sun.
Time Charter#
Hiring a ship (with crew) for a period of time, the charterer directing its employment.
Tonnage#
A measure of a ship’s size, gross or net, based on enclosed volume rather than weight.
Toolbox Talk#
A short safety briefing held before a task to review its hazards and controls with those involved.
Track#
The intended or actual path of a vessel over the ground.
Traffic Separation Scheme (TSS)#
A routeing measure separating opposing streams of traffic into lanes to reduce collision risk.
Transit#
Two fixed objects seen in line, giving a precise position line or a leading line into harbour.
Trim#
The difference between the forward and after draughts; the longitudinal attitude of a ship.
Tropical Revolving Storm#
An intense tropical low-pressure system — hurricane, typhoon or cyclone — to be avoided at sea.
True Bearing#
A bearing measured clockwise from true north.
Twilight#
The period of partial light at dawn and dusk; nautical twilight is when star sights are taken.
U (4 TERMS)
Ullage#
The empty space above the liquid in a tank; measured to calculate the quantity carried.
Under-Keel Clearance (UKC)#
The depth of water beneath the keel — the actual depth of water less the ship’s draught.
Underway#
A vessel that is not at anchor, made fast to the shore, or aground.
UTC#
Coordinated Universal Time — the time standard used at sea for navigation and communications.
V (6 TERMS)
Variation#
The angle between true and magnetic north at a place, changing with position and slowly over time.
Veer#
To pay out cable or rope; also a clockwise change in wind direction.
Vertical Sextant Angle#
A sextant angle of an object of known height, used to calculate distance off.
VHF#
Very High Frequency radio — the principal medium for short-range ship-to-ship and ship-to-shore communication.
Voyage Charter#
Hiring a ship for a specific voyage to carry a stated cargo, paid by freight.
VTS (Vessel Traffic Service)#
Shore-based monitoring and management of ship traffic in busy or confined waters.
W (13 TERMS)
Wake#
The track of disturbed water left astern by a moving vessel.
Warm Front#
The leading edge of advancing warm air rising over colder air, bringing prolonged cloud and rain.
Warp#
To move a ship by hauling on ropes made fast to fixed points ashore or to anchors.
Watch#
A division of the day during which part of the crew is on duty; also the personnel on duty.
Watch System#
The rota dividing the day into watches so the ship is continuously and safely manned.
Watchkeeping#
The system of maintaining a continuous, alert lookout and control of the ship in shifts. Read the full watchkeeping guide ›
Watertight Door#
A door built and maintained to prevent water passing between compartments.
Watertight Integrity#
The maintenance of a ship’s structure and closures to keep water out and preserve buoyancy and stability.
Waypoint#
A position marking a point on the planned route where a course alteration or event occurs.
Whipping#
A binding worked onto a rope’s end to stop the strands fraying.
Williamson Turn#
A shiphandling manoeuvre that turns the ship onto a reciprocal course to return to a point, used chiefly to recover a person overboard.
Windlass#
The deck machine used to heave in and pay out the anchor cable.
Windward#
The side or direction from which the wind blows; the opposite of lee.
Y (1 TERM)
Yaw#
The rotational motion of a ship about its vertical axis, swinging the bow off the intended course.
Z (1 TERM)
ZOC (Zone of Confidence)#
An ENC rating of the accuracy and reliability of the survey data behind a charted area.