MARINA Chief Mate / Master Theoretical Exam key terms

The direction of an object measured clockwise from true north, expressed in degrees from 000 to 360, corrected for variation and deviation so it references geographic north rather than compass north.

The angular difference at a given place between true north and magnetic north, caused by the Earth's magnetic field; it changes with position and slowly with time and is taken from the chart's compass rose.

The angle between magnetic north and the north indicated by a particular ship's compass, caused by the vessel's own magnetic fields and varying with the ship's heading; it is recorded on a deviation table.

The process of estimating a vessel's position by advancing a known starting position using courses steered and speeds through the water over elapsed time, without reference to external position fixes.

The actual direction of a vessel's movement over the seabed, derived from successive position fixes; it differs from the course steered whenever current or wind pushes the vessel sideways.

Set is the direction toward which a current flows, and drift is its speed, usually expressed in knots; together they describe the current's effect on the vessel's track over the ground.

The vertical distance between the lowest point of a vessel's hull and the seabed, allowing for squat, tide, swell and charted depth; it is a key factor in safe passage planning in shallow or confined waters.

The reduction in under keel clearance experienced by a vessel moving through water, caused by increased flow velocity and lowered pressure beneath the hull; it increases with speed and in shallow water.

The tendency of a vessel moving close to a bank or channel edge to be drawn toward it while its bow is pushed away, caused by unequal water pressure and flow around the hull.

The horizontal reference level to which depths and drying heights on a nautical chart are reduced, normally approximately lowest astronomical tide, so that charted depths are usually conservative.

A period during which the combination of tide height, vessel draft and required under keel clearance allows safe transit of a shallow area such as a bar, lock or port approach.

The volume occupied by one unit of mass of a cargo, usually expressed in cubic metres per tonne; it determines whether a cargo is volume-limited or weight-limited in a hold.

The space in a cargo hold that is wasted because packages or cargo units do not fit together perfectly, expressed as a percentage of the total volume not occupied by cargo.

The total mass a vessel can carry when loaded to her permitted load line, comprising cargo, bunkers, fresh water, ballast, stores and crew; it is the difference between loaded and light displacement.

Material such as timber, mats or inflatable bags placed under and between cargo to spread weight, allow ventilation, prevent shifting and protect cargo from contact with the ship's structure or moisture.

A ship-specific document approved by the flag administration that specifies the equipment, arrangements and procedures for safely securing cargo, and which must be followed during stowage and lashing.

The assessment of forces acting on a cargo unit and the strength and number of lashings required to resist them, typically following methods accepted under the CSS Code and the ship's securing manual.

The mark assigned under the International Convention on Load Lines showing the maximum permitted draft for a vessel in specified zones and seasons, ensuring adequate freeboard and reserve buoyancy.

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

The volume of the watertight hull above the waterline, which allows a vessel to rise when weight is added or when she ships water, and which is a principal measure of survivability after damage.

The distance between the centre of gravity and the transverse metacentre; a positive value indicates initial stability, with larger values giving stiffer roll and smaller values a tender, slower roll.

The horizontal distance between the centre of gravity and the centre of buoyancy when a vessel is heeled, which multiplied by displacement gives the righting moment tending to return the ship upright.

The apparent rise in a vessel's centre of gravity caused by liquid moving freely in a partially filled tank, reducing metacentric height and stability; it is minimised by keeping tanks either full or empty.

The maximum length of a compartment that may be flooded without immersing the margin line, used in damage stability calculations to determine permissible compartment subdivision along the vessel.

The ability of a vessel to remain afloat and upright after flooding of one or more compartments, assessed against criteria for residual freeboard, heel and range of positive stability.

The document required by SOLAS that assigns each person on board specific duties and a muster station in an emergency, including substitutes for key personnel who may be unavailable.

The person or vessel designated to coordinate search and rescue operations within a specified area, usually appointed by the search and rescue mission coordinator or assumed by the first vessel to arrive.

The official designated by a rescue coordination centre to be responsible for the overall conduct of a search and rescue operation, including planning, tasking of units and termination of the operation.

A distress beacon, normally operating on 406 MHz to alert the COSPAS-SARSAT system and on 121.5 MHz for homing, which transmits the vessel's identity and position when activated in an emergency.

The international system of satellite and terrestrial radio communications, including digital selective calling and NAVTEX, that provides distress alerting, urgency, safety and routine communications at sea.

A radiotelephone technique using coded digital signals on VHF, MF and HF to transmit distress alerts and establish contact with specific stations, with dedicated distress buttons and stored identities.

A navigation system that displays official vector electronic navigational charts with the vessel's position from GNSS, providing automatic alarms for safety contours, isolated dangers and route deviations.

A transponder system that broadcasts and receives vessel identity, position, course, speed and voyage data over VHF, used for collision avoidance, traffic monitoring and search and rescue.

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

A weather map showing the distribution of pressure systems, fronts, isobars and weather phenomena over a large area at a stated time, used to forecast wind and weather along a planned route.

An intense low-pressure system forming over warm tropical oceans, with a calm eye and destructive winds around it; in the northern hemisphere it is avoided by keeping the wind on the starboard bow.

A description of the roughness of the sea surface, commonly coded by significant wave height under the World Meteorological Organization scale and reported alongside wind force in weather observations.

A certificate issued by the flag administration stating the minimum number and qualifications of personnel required to operate the vessel safely, taking account of automation and trading area.

The ISM Code requires companies and ships to operate a documented safety management system covering policy, responsibilities, risk assessment, emergency preparedness and internal audits.

Inspection of foreign vessels in port by the coastal state to verify compliance with international conventions, with deficiencies leading to detention until rectified.

The state whose nationality a vessel holds and which is responsible for enforcing international conventions on that vessel, including surveys, certification and manning requirements.

An international convention governing bills of lading that sets out carrier obligations of seaworthiness and care of cargo, together with defences and package limitation of liability.

A principle of maritime law under which extraordinary expenses or sacrifices intentionally incurred to save a common maritime adventure are shared proportionately among ship, cargo and freight interests.

A document issued by the carrier acknowledging receipt of goods for shipment, evidencing the contract of carriage and acting as a document of title that must be surrendered to obtain delivery.

The difference between the theoretical distance a propeller would advance in one revolution and the actual advance through the water, expressed as a percentage of the theoretical advance.

A boiler producing steam for ship services such as fuel heating, tank cleaning, accommodation heating and fresh water generation, separate from the main propulsion plant.

An electrical generator driven from the main propulsion shaft, using engine power to produce electricity at sea and reducing the load on auxiliary diesel generators.