Norway Deck Officer Class 5 key terms

The vertical distance between a ship's centre of gravity and its metacentre. A positive value gives an initial righting moment when the ship heels; a small or negative value indicates poor or unstable transverse stability.

The horizontal distance between the centre of gravity and the vertical line through the centre of buoyancy at a given angle of heel. Multiplied by displacement and gravity it gives the righting moment.

The apparent rise in a ship's centre of gravity caused by liquid moving freely in a partly filled tank as the ship heels. It reduces effective metacentric height and can seriously impair stability.

The angle to which a ship with negative initial stability heels and then rests, because the centre of buoyancy has shifted enough to create a righting moment. It is unstable equilibrium, not a safe list.

Marks on the ship's side showing the maximum permitted draught in different seasons and water densities, assigned under the International Convention on Load Lines. They protect reserve buoyancy and structural strength.

The watertight volume of a ship above the waterline, expressed as a volume or percentage of total volume. It allows the ship to rise after damage or extra weight and is linked to the assigned load line.

The total weight a ship can carry when loaded to its permitted summer draught, comprising cargo, bunkers, fresh water, ballast, stores and crew. It equals loaded displacement minus lightship displacement.

A ship's ability to stay afloat and upright after one or more compartments are flooded. It is assessed against subdivision and survivability criteria in SOLAS, including residual freeboard and heel limits.

The condition in which openings such as doors, hatches, vents and scuppers are closed or secured so that water cannot pass into or between compartments. It is maintained through a closure and inspection routine.

A radar navigation technique in which a fixed range and bearing from a charted object is transferred to the radar display and the vessel's position relative to that line is monitored continuously, giving an immediate indication of cross-track error.

A radar or ECDIS display mode in which echoes are referenced to a fixed geographical position rather than to the ship's heading. It keeps land and fixed objects steady while the vessel moves across the picture.

The actual direction of a vessel's movement over the seabed, derived from successive position fixes. It differs from the heading when current or wind pushes the vessel sideways.

The rate at which a vessel moves across the seabed, as opposed to speed through the water. It is used for passage planning, ETA calculations and traffic assessment in areas affected by current.

Set is the direction towards which a current flows; drift is its speed. Together they describe the current's effect, which must be allowed for when converting between course to steer and course made good.

A computer-based navigation system that displays official vector or raster charts with the vessel's position and can give safety-contour and route alarms. Its use requires type-specific training and documented procedures.

The process of designing a passage with waypoints, courses and margins that keep the vessel clear of hazards, traffic separation schemes and restricted areas, taking account of draught, weather and contingency anchorages.

The vertical distance between the lowest point of the hull and the seabed. It must be maintained above a calculated minimum, allowing for squat, tide, swell and chart accuracy.

The reduction in under-keel clearance and change of trim experienced by a vessel moving through shallow water. It increases with speed and block coefficient and is greatest in confined channels.

The interaction between a moving vessel and a nearby bank or channel side, producing a turning moment and sideways suction. It is strongest in narrow, shallow waterways and at higher speeds.

The point about which a vessel appears to rotate when turning or when forces act on it. Its position shifts with speed and rudder angle, which affects how the bow and stern swing alongside a berth.

The use of harbour tugs to push, pull or hold a vessel during berthing, unberthing or confined manoeuvring. Tug bollard pull and attachment points determine the forces that can be applied.

A situation in which another vessel's compass bearing stays steady while the range falls. Under the collision regulations it indicates risk of collision and usually means the vessels are on converging courses.

A condition that exists when two vessels approach so closely that their courses and speeds may bring them together. It must be treated as present if there is doubt, and a steady bearing is strong evidence of it.

The vessel required by the steering and sailing rules to keep out of the way of another. It must take early and substantial action, normally passing astern, and must not cross ahead if that risks collision.

The vessel entitled to hold its course and speed while another keeps clear. It must nevertheless take action if the give-way vessel fails to do so, and may act as soon as collision cannot be avoided by that vessel alone.

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

A continuous watch by sight and hearing and by all available means, including radar and VHF where appropriate, to detect other vessels, hazards and changes in conditions. It must be maintained at all times.

The formal briefing given by an outgoing officer of the watch to the relieving officer, covering position, course, traffic, weather, machinery status, orders and any standing instructions affecting the next watch.

Written instructions from the master setting out the conditions under which the officer of the watch must call the master, together with minimum safety margins for course, position and weather.

A SOLAS-linked code requiring companies to operate a documented safety management system with defined responsibilities, procedures for key shipboard operations, and reporting and analysis of accidents and non-conformities.

The principal international treaty on ship construction, life-saving appliances, fire protection, radio equipment, navigation safety and voyage planning. It is implemented through certificates and surveys by flag administrations.

Inspection of foreign ships in a port by the coastal authority to verify that certificates and actual conditions comply with international conventions. Deficiencies may lead to detention until they are rectified.

The volume occupied by one tonne of a given cargo, usually expressed in cubic metres per tonne. It determines whether a cargo is heavy or light and therefore how a hold's volume and deadweight are used.

A ship-specific document approved by the flag administration that specifies how cargoes, including containers and heavy units, must be stowed and lashed for the intended voyage. Its instructions are mandatory.

A document from the shipper giving the proper shipping name, UN number, class, packing group, quantity and emergency information for dangerous goods. It is required before such cargo may be loaded.

The international code governing classification, packing, marking, labelling, stowage, segregation and documentation of packaged dangerous goods carried by sea. It is given mandatory effect through SOLAS and MARPOL.

A document assigning every person on board specific duties and a designated station for emergencies such as fire, abandon ship or man overboard. It is posted throughout the ship and practised in drills.

A permanently displayed plan showing the location of fire sections, alarms, extinguishing appliances, escape routes and ventilation controls. It is used by the crew and by shore firefighting services.

An independent power source that starts automatically on loss of main power and supplies essential services such as emergency lighting, steering gear, radio and alarms. Its readiness is verified by regular testing.