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 — search it, or browse A–Z.
Start here · The most common terms
If you learn only a handful of nautical terms, learn these — the directions, parts and measurements you will hear within minutes of stepping aboard any ship.
Portthe left-hand side of a ship when facing forward
Starboardthe right-hand side of a ship when facing forward
Bowthe front end of the ship
Sternthe rear end of the ship
Fore / Forwardtoward the bow
Aft / Asterntoward, or behind, the stern
Amidshipsthe middle of the ship
Beamthe width of the ship at its widest point
Keelthe structural backbone along the bottom of the hull
Bridgethe command centre from which the ship is navigated
Helmthe wheel or tiller used to steer the ship
Knota unit of speed: one nautical mile per hour
Nautical Milea distance of 1,852 metres (about 1.15 land miles)
Draught (Draft)how deep the ship sits in the water
Freeboardthe height of the hull above the waterline
Underwaynot anchored, moored, or aground — free to move
Windward and Leewardthe side the wind comes from, and the sheltered side away from it
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A
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
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
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
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
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
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
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
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
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
K
L
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
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
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
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
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
Quarter#
The part of a ship’s side towards the stern, between the beam and the stern.
R
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
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
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
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
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
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
Yaw#
The rotational motion of a ship about its vertical axis, swinging the bow off the intended course.
Z
ZOC (Zone of Confidence)#
An ENC rating of the accuracy and reliability of the survey data behind a charted area.