BD Deck Officer Class 3 (OOW) key terms

A method of estimating a vessel's position by advancing the last known position using courses steered and speeds through the water, without correcting for current or wind.

The most probable position of a vessel obtained by applying estimated current and leeway effects to a dead reckoning position, giving a better answer than DR alone.

The actual direction of travel of a vessel over the seabed, derived from successive GPS fixes; it differs from the course steered when current or wind pushes the vessel sideways.

Set is the direction toward which a current flows; drift is the speed of that current, usually expressed in knots. Together they describe tidal stream or current effect on the vessel.

The horizontal reference level on a nautical chart from which depths and drying heights are measured, normally approximately the lowest astronomical tide so that actual depths are usually greater than charted.

The depth of water shown on a nautical chart, measured downward from chart datum, not from the actual sea surface; the true depth is charted depth plus height of tide.

The vertical distance between the actual sea surface at a given time and chart datum; added to charted depth it gives the actual depth of water available.

Two lights arranged so that, when seen in line from a vessel, they indicate a safe channel or approach direction; they are usually marked on charts with the bearing between them.

A buoy or beacon whose topmark and colour pattern indicate the direction of safe water relative to the mark, named north, east, south or west according to where the safe water lies.

The international system of buoyage using lateral and cardinal marks, defining which side of a channel to pass and where safe water lies, with two regions differing in lateral mark colour order.

A navigation light that shows different colours or characteristics over defined arcs, allowing a mariner to identify safe water, dangers or the channel by the colour seen.

A sudden, sharp increase in wind speed, often with a change of direction and heavy precipitation, typically associated with cumulonimbus cloud and lasting minutes to a few hours.

A towering, dense cloud with a flat anvil top, associated with thunderstorms, heavy rain, hail, lightning and violent squalls; it is a major hazard to small vessels and to deck operations.

A suspension of water droplets near the surface reducing horizontal visibility below one kilometre; it forms when moist air cools to its dew point and is a major collision hazard.

A scale from 0 to 12 describing wind force from calm to hurricane, based on observable effects on the sea surface and, historically, on the sails a vessel could carry.

A meteorological message issued to warn of forecast or observed storm-force winds, allowing masters to plan route changes, cargo securing and deck preparations before conditions deteriorate.

The virtual rise in a vessel's centre of gravity caused by liquid moving freely in a partly filled tank, reducing effective metacentric height and stability; it is greatest in wide tanks.

The vertical distance between a vessel's centre of gravity and its metacentre; a positive value indicates initial stability, and larger values mean stiffer, more rapid rolling.

The vertical distance from the waterline to the freeboard deck at side, measured at amidships; it indicates reserve buoyancy and is controlled by load line rules.

The volume of enclosed watertight space above the waterline that can be flooded before the vessel sinks; it is protected by watertight subdivision and by maintaining adequate freeboard.

The point through which the total weight of the vessel and its contents acts vertically downward; its height and position determine trim, list and stability.

The condition of a vessel in which all openings that could admit water are closed or secured, preserving subdivision and reserve buoyancy; it is maintained through a closing-appliance schedule.

The mark on a vessel's side, with seasonal lines and deck line, showing the maximum permitted draught in different seasons and zones; it safeguards reserve buoyancy and structural strength.

The volume in cubic metres occupied by one tonne of a particular cargo in its stowed condition; it determines whether a cargo is heavy or light relative to the ship's capacity.

The space in a cargo hold lost because cargo packages and the hold shape do not fit perfectly; it reduces the volume actually available for cargo and must be allowed for in planning.

The physical separation of incompatible cargoes, such as dangerous goods reacting with one another, achieved by distance, intervening compartments or deck stowage according to the applicable code.

The International Maritime Dangerous Goods Code, which classifies hazardous cargoes and sets requirements for packing, marking, labelling, stowage, segregation and documentation for sea transport.

A document from the shipper identifying a dangerous cargo by proper shipping name, UN number, class, packing group and quantity, so the ship can plan safe stowage and segregation.

The total weight a vessel can carry when loaded to her permitted summer draught, comprising cargo, bunkers, fresh water, ballast, stores and crew, expressed in tonnes.

A document assigning each crew member specific emergency duties and a designated station, ensuring an organised and rapid response to fire, abandon-ship, man-overboard or other emergencies.

A certificate issued by the flag State specifying the minimum number and qualifications of crew required to operate the vessel safely, taking account of ship type and trading area.

A document issued by a maritime authority certifying that the holder has met the training, examination and sea service requirements to serve in a specified rank or capacity.

The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers, setting minimum competence, rest hour and certification requirements for seafarers worldwide.

The colloquial name for the collision regulations, comprising steering and sailing rules, lights and shapes, and sound and light signals governing vessel conduct to prevent collisions.

A vessel required to keep out of the way of another; it must take early and substantial action to keep well clear and, in crossing situations, normally avoid crossing ahead.

A vessel that has the right of way and must keep her course and speed, while remaining alert; she may take action only when collision risk is so close that the give-way vessel is not acting.

Any condition in which visibility is reduced by fog, mist, falling snow, heavy rain or similar causes, requiring reduced speed, sound signals and a proper lookout by all available means.

The speed at which a vessel can take proper and effective action to stop within a distance appropriate to the prevailing circumstances and conditions, including visibility, traffic and draught.

The operation of taking aboard fuel oil; it requires a agreed plan, checking tanks and valves, communications with the supplier, drip trays and watch for leaks throughout the transfer.

The Shipboard Oil Pollution Emergency Plan, a required document setting out procedures, contacts and equipment for responding to an oil spill from the vessel.

A mandatory record of all oil-related operations on board, such as bunkering, transfers, discharges and disposal, kept for inspection to demonstrate compliance with pollution regulations.

The International Convention for the Prevention of Pollution from Ships, containing annexes controlling pollution by oil, noxious liquids, harmful substances, sewage, garbage and air emissions.

A sea area defined under MARPOL where stricter discharge controls apply because of its oceanographic and ecological condition and its importance for traffic, requiring more careful waste management.

A required on-board plan giving procedures for collecting, processing, storing and discharging ship-generated garbage in accordance with MARPOL, including placards and a garbage record book.

A document issued by the carrier acknowledging receipt of goods for shipment, evidencing the contract of carriage and acting as a document of title when made negotiable.

An international convention defining the carrier's minimum duties and liabilities for cargo carried under a bill of lading, including the duty to exercise due diligence to make the ship seaworthy.

A contract between a shipowner and a charterer for the hire or use of a vessel, setting out the vessel's description, employment, duration, hire or freight, and the allocation of costs.

The Global Maritime Distress and Safety System, an international system using satellite and terrestrial radio communications for distress alerting, search and rescue coordination and maritime safety information.

A radio facility on VHF, MF and HF that transmits coded digital alerts, including distress alerts with vessel identity and position, to selected stations or all stations.

An Emergency Position Indicating Radio Beacon that, when activated, transmits a distress alert with the vessel's identity to the COSPAS-SARSAT satellite system for relay to rescue authorities.

A Search and Rescue Transponder that, when interrogated by a radar, displays a series of dots on the rescuing vessel's radar screen to indicate the position of a survival craft.

A terrestrial system broadcasting maritime safety information such as navigational warnings and weather forecasts to vessels within range, received automatically by a dedicated receiver.

A structured set of procedures and checklists for dealing with identified emergency scenarios, specifying alarm signals, duties, communications and coordination with shore authorities.

The person designated to coordinate search and rescue operations of several vessels or units within a defined area, usually appointed by the rescue coordination centre.

The final emergency measure of leaving a vessel that cannot be saved, ordered by the master, with crew proceeding to survival craft carrying distress equipment and following the muster list.

A dangerous fall in core body temperature below about 35 degrees Celsius, causing shivering, confusion and loss of consciousness, common after immersion in cold water.

The sudden physiological response to cold water immersion, including gasping, hyperventilation and rapid heart rate, which can cause drowning within the first minutes of immersion.

Deterioration after a near-drowning incident, when water in the lungs causes inflammation or infection hours later; victims therefore need medical assessment even if they seem recovered.