GMA OOW Deck key terms

The actual direction of travel of a vessel over the seabed, derived from GPS or by combining heading with the effects of current, wind, and leeway. It differs from the heading shown by compass.

The speed at which a vessel moves relative to the seabed, as measured by GPS or calculated from fixes. It includes the effect of current and differs from speed through the water.

The method of estimating a vessel's position by advancing the last known fix using courses steered and distances run through the water, without reference to external landmarks or celestial bodies.

The best possible position derived from dead reckoning corrected for known factors such as current, leeway, and tidal stream. It is less reliable than a fix but more accurate than raw dead reckoning.

The sideways drift of a vessel downwind of its intended track, caused by wind pushing against the hull and superstructure. It is applied as a correction to the course steered when plotting.

The angular difference between true north and magnetic north at a given location, caused by the Earth's magnetic field. It is shown on charts and changes slowly over time.

The error in a magnetic compass caused by the vessel's own magnetic fields, arising from hull material and electrical equipment. It varies with the vessel's heading and is recorded on a deviation card.

The total algebraic sum of variation and deviation, applied to convert between compass and true bearings. It is named east or west depending on whether the compass reads low or high.

The horizontal movement of water caused by tidal forces, described by set and drift. Its effect must be accounted for in passage planning and position fixing.

The two components describing a current or tidal stream: set is the direction toward which the water flows, expressed in degrees true, and drift is its speed, usually in knots.

The principal international treaty governing the construction, equipment, and operation of merchant ships. It sets minimum safety standards covering fire protection, life-saving appliances, radio equipment, and navigation safety.

A mandatory framework under SOLAS requiring shipping companies to establish a safety management system. It defines company and shipboard responsibilities, documentation, and procedures for safe operation and pollution prevention.

A certificate issued to an individual ship confirming that its safety management system complies with the ISM Code. It is valid for five years subject to intermediate verification by the flag administration or recognised organisation.

A certificate issued to a shipping company confirming that its shore-based safety management system meets the ISM Code. A copy must be carried on board each of the company's ships.

The convention setting minimum standards for training, certification, and watchkeeping of seafarers. It governs certificates of competency, rest hours, and mandatory basic safety training for all crew.

A document issued by a flag administration certifying that the holder meets the standards of competence required for the rank and capacity stated. It must be revalidated periodically under STCW requirements.

The International Convention for the Prevention of Pollution from Ships, covering oil, noxious liquid substances, harmful packaged goods, sewage, garbage, and air pollution. It requires record books, equipment, and discharge restrictions.

A mandatory register in which all oil transfer, discharge, and disposal operations on board are recorded. Entries must be signed by the officer in charge and the master, and the book is subject to inspection by port state control.

The inspection of foreign-flagged ships in national ports to verify compliance with international conventions. Deficiencies may lead to detention until rectified, and results are shared through regional memoranda of understanding.

A shipboard document required under MARPOL Annex V setting out procedures for collecting, processing, storing, and discharging garbage. It designates a responsible officer and must be available to all crew.

An internationally coordinated system using satellite and terrestrial radio to ensure that distress alerts are received and rescue coordinated anywhere at sea. It defines sea areas A1 to A4 and the equipment required in each.

A radio technique using coded digital messages on VHF, MF, and HF to initiate distress, urgency, and routine calls. It transmits the vessel's identity and the nature of the alert automatically.

A float-free transmitter that, when activated, sends a distress alert with the vessel's identity via satellite to rescue coordination centres. It is registered to a specific vessel and must be tested periodically.

A portable radar transponder carried on survival craft that responds to interrogating radar with a distinctive line of blips, helping rescuers locate the craft. It operates in the 9 GHz radar band.

A distress call transmitted by a station other than the vessel in distress, on its behalf, when the original distress message has not been acknowledged. The relaying station must identify itself and the source of the alert.

The vertical distance measured at the ship's side from the waterline to the upper edge of the deck line. It indicates reserve buoyancy and is controlled by the load line assignment.

The mark painted on the ship's side showing the maximum permitted draught in different seasonal and regional zones. It is assigned by a classification society or flag administration under the Load Line Convention.

The volume of enclosed watertight space above the waterline that can be flooded before the vessel sinks. It provides the ship's ability to withstand damage and is reduced by excessive deck cargo or free surface.

The apparent loss of metacentric height caused by liquid shifting freely in a partly filled tank when the ship heels. It reduces stability and is minimised by keeping tanks either full or empty.

The distance between the centre of gravity and the metacenter, used as a measure of initial transverse stability. A positive GM indicates a stable ship; excessive GM produces a stiff, uncomfortable roll.

The angle at which a ship with negative initial metacentric height comes to rest in stable equilibrium, either to port or starboard. It is corrected by lowering the centre of gravity, for example by filling low tanks.

The internal forces induced in a ship's hull by the distribution of weight and buoyancy along its length. Excessive values cause hogging, sagging, or structural failure and must be monitored during loading.

Longitudinal bending of the hull where hogging means the ends are supported less than the middle, causing the keel to sag, and sagging is the reverse. Both arise from uneven weight distribution and can overstress the structure.

The volume occupied by unit mass of a cargo, usually expressed in cubic metres per tonne. It determines whether a cargo is heavy or light and how the hold space should be allocated.

A document prepared by the shipper describing a dangerous consignment, including its proper shipping name, UN number, class, packing group, and emergency procedures. It is required under the IMDG Code before loading.

The mandatory code governing the classification, packing, marking, labelling, stowage, and segregation of dangerous goods carried by sea. It is updated regularly and forms part of SOLAS chapter VII.

The required physical separation between incompatible dangerous goods, or between dangerous goods and other cargo, to prevent dangerous reactions. It is expressed in degrees such as away from, separated from, or separated by a complete compartment.

A GMDSS sea area within radio range of at least one VHF coast station providing continuous DSC alerting, typically about 20 to 30 nautical miles from the coast. VHF equipment is the minimum requirement there.

The organised system of maintaining a continuous navigational and engineering watch while the ship is underway or in port. Under STCW it prescribes minimum rest hours and the duties of the officer of the watch.

The document assigning each crew member to specific duties and stations during emergencies such as fire, abandon ship, or man overboard. It must be posted prominently and practised in regular drills.

A periodic exercise in which the crew practises launching survival craft, donning immersion suits, and mustering at designated stations. SOLAS sets the required frequency and requires records to be kept.

A designated location on board where crew and passengers assemble during an emergency or drill. It is marked on the muster list and on shipboard plans, with clear signage and access routes.

The procedure for entering tanks, holds, or voids where the atmosphere may be oxygen-deficient or contain toxic or flammable gas. It requires a permit, atmosphere testing, ventilation, and a standby person outside.

An intense low-pressure system with organised circulation that forms over warm tropical oceans and can produce destructive winds, heavy rain, and high seas. Vessels avoid the storm centre and dangerous semicircle by altering course early.

The half of a tropical cyclone lying to the left of its track in the northern hemisphere and to the right in the southern hemisphere, where winds and seas are most hazardous. Vessels should avoid it and steer to the navigable semicircle.

A numerical scale from 0 to 12 describing wind force based on observed sea conditions and its effect on objects. It is used in weather reports and ship logs to standardise wind descriptions.

The change in atmospheric pressure over the past three hours, reported with its characteristic pattern in weather observations. A rapidly falling tendency often signals an approaching depression or storm.

A compression-ignition engine completing a power cycle in one revolution, with scavenging and exhaust occurring through ports and valves. It offers high power-to-weight ratio and is common as main propulsion on large ships.

An engine completing a power cycle in two revolutions, with separate intake, compression, power, and exhaust strokes. It is typically used for auxiliary generators and smaller vessels.

The arrangement of tanks, pumps, heaters, filters, and purifiers that supplies clean fuel at the correct viscosity and pressure to the engines. Deck officers must understand it for bunkering and pollution prevention.

The transfer of fuel oil from a supply barge or shore facility to a ship's tanks. It requires a pre-transfer checklist, agreed communication, scuppers plugged, and careful monitoring to prevent overflow and pollution.

The control of water taken on board for stability to prevent the transfer of harmful aquatic organisms between ports. It requires treatment to the D-2 standard or exchange under the Ballast Water Management Convention.