MAJ OOW Deck Exam key terms

The angular difference between true north and magnetic north at a given place, caused by the Earth's magnetic field and shown on charts as an annual rate of change.

The error in a ship's magnetic compass caused by the vessel's own steel and electrical equipment, varying with the ship's heading and corrected using a deviation card.

The algebraic sum of variation and deviation, applied to a compass bearing to convert it to a true bearing, with easterly error added and westerly error subtracted.

A direction measured clockwise from true north, independent of magnetic influences, and the reference used for plotting positions and courses on a chart.

The angle measured clockwise from the ship's heading to a target, so that true bearing equals heading plus relative bearing, used in visual and radar plotting.

A position fix obtained by advancing an earlier line of position along the course and distance run, then crossing it with a later line of position from a different object.

A locus of points where the ship must lie, derived from a bearing, range, or celestial observation, and drawn on the chart to establish the vessel's position.

The small triangle formed when three position lines fail to meet at one point, indicating a small error; the vessel's position is taken at its centre.

A systematic record of target bearings and ranges over time, used to derive the closest point of approach and time of closest point of approach for collision avoidance decisions.

Closest point of approach: the minimum predicted distance between own ship and a target vessel, calculated from relative motion and used to judge collision risk.

A situation where the bearing of an approaching vessel does not appreciably change, requiring the give-way or stand-on action prescribed by the collision regulations.

The vessel required to keep out of the way of another by taking early and substantial action, such as altering course to starboard or reducing speed.

The vessel that must keep her course and speed, but may take action to avoid collision once it becomes clear the give-way vessel is not taking appropriate action.

A restricted waterway where vessels must keep as near the starboard outer limit as is safe and practicable, and avoid crossing if it impedes other traffic.

A routing measure approved by the competent authority, using separation zones and lanes, in which through traffic follows the established direction of flow.

The speed at which a vessel can take proper and effective action to stop or avoid collision, determined by visibility, traffic density, and stopping distance.

Any condition where visibility is reduced by fog, mist, snow, or rain, requiring sound signals, a safe speed, and radar observations as prescribed by the rules.

A sound signal sounded in restricted visibility to warn other vessels of presence and manoeuvring state, such as one prolonged blast for a power-driven vessel making way.

A numerical scale from 0 to 12 describing wind strength by its observable effects on the sea surface, used in weather reporting and ship observations.

A description of the condition of the sea surface, usually given by wave height and period, classified on a scale from calm to very high.

Long-period waves that have travelled away from their generating area, producing regular undulations that may arrive from a different direction than the local wind.

A weather map showing isobars, pressure systems, and fronts at a stated time, used to forecast wind direction and strength along a planned route.

A line on a weather chart joining points of equal atmospheric pressure; closely spaced isobars indicate strong winds and a steep pressure gradient.

The vertical distance from the waterline to the freeboard deck at side, indicating reserve buoyancy and required to meet the load line marks.

The watertight volume above the waterline that can be flooded before the vessel sinks, providing the margin of safety when cargo or water is added.

The set of marks on the ship's side showing the maximum permitted draught in different seasons and water densities, assigned under the load line convention.

The distance between the centre of gravity and the metacenter, a measure of initial transverse stability; a small positive value gives a stiff or tender ship.

The horizontal distance between the centre of buoyancy and the centre of gravity when a vessel is heeled, producing the moment that returns her upright.

The point where the total weight of the ship and its contents acts vertically downwards, shifting when weights are loaded, discharged, or moved.

The apparent rise in the centre of gravity caused by liquid moving freely in a partly filled tank, reducing stability; minimised by keeping tanks pressed up or empty.

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 negotiable.

An international convention setting out the carrier's minimum duties, defences, and limits of liability for cargo carried under a bill of lading.

A principle in maritime law where losses and expenses deliberately incurred to save a ship and cargo from a common peril are shared proportionately by all parties.

The lashing, stowage, and planning measures that keep cargo in place against ship motion, in accordance with the Cargo Securing Manual and safe stowage requirements.

The International Convention for the Prevention of Pollution from Ships, covering oil, noxious liquids, harmful substances, sewage, garbage, and air pollution through its annexes.

A mandatory record in which all oil transfers, discharges, and disposal operations are logged and signed, open to inspection by port state control officers.

A shipboard plan required under MARPOL that sets out procedures for collecting, processing, storing, and discharging garbage in accordance with the applicable annex.