Norway Deck Officer Class 1 (Master Mariner) key terms

The shortest path between two points on the Earth's surface, following an arc of a great circle. It requires continuous course changes unless plotted as a series of rhumb-line legs.

A line crossing every meridian at the same angle, appearing straight on a Mercator chart. It is easier to steer but longer than a great-circle route except along the equator or a meridian.

The point of highest latitude reached on a great-circle track, where the course is exactly 090° or 270°. It marks where the track turns and is used to check ice and weather exposure.

A cylindrical chart projection on which meridians are parallel straight lines and latitude scale expands towards the poles. Courses and bearings plot as straight lines, but distances must be measured from the latitude scale at the same latitude.

Techniques such as RAIM, SBAS and receiver autonomous checks that detect when a satellite positioning fix is unreliable. It allows the watchkeeper to know whether the displayed position can be trusted.

A type-approved navigation system that displays official vector or raster charts with own-ship position, safety contours and alarms. Its settings and limitations must be understood before it is relied on for navigation.

A radar technique in which the range of a fixed feature abeam is monitored to confirm the vessel keeps a constant distance off a coastline or hazard, particularly in reduced visibility.

A position obtained from visual bearings or ranges of charted objects, independent of satellite systems. It is the standard cross-check when electronic positioning is suspect.

A low-pressure system formed along a front between contrasting air masses, with associated warm, cold and occluded fronts. It brings veering or backing winds, precipitation and often rapid pressure falls.

The change in atmospheric pressure over the past three hours, reported with its characteristic pattern. A falling tendency indicates approaching bad weather; a rapid fall suggests a deep or fast-moving low.

A scale from 0 to 12 describing wind force by observable sea state and its effect on a vessel. It is used in weather reports and logs to convey wind strength without instruments.

The mean height of the highest one-third of waves in a sea state, roughly the height an experienced observer reports. It is used in forecasts and for assessing heavy-weather routing decisions.

A coastal or high-seas bulletin issued when winds of storm force are expected or occurring. It triggers specific obligations to inform the master and take heavy-weather precautions.

The loss of effective metacentric height caused by liquid shifting in a partly filled tank as the ship heels. It reduces stability and must be accounted for in the loading condition.

The vertical distance between the centre of gravity and the transverse metacenter. A small positive value gives a stiff or tender ship; a negative value indicates initial instability.

The angle to which a ship with negative initial stability heels and settles in still water. The vessel is unstable upright but stable at that angle, and corrective measures must be taken carefully.

Large rolling motion excited when the encounter frequency of waves is about twice the ship's natural roll frequency, common in following seas. It is a serious risk for container ships and requires course or speed change.

The reduction in under-keel clearance caused by increased water velocity beneath a moving hull, greatest in shallow water and at high speed. It increases draught aft and can cause grounding.

The tendency of a vessel to be drawn towards a nearby bank and to turn its bow away from it, caused by asymmetric pressure around the hull. It is strongest in narrow, shallow channels.

The hydrodynamic forces between two vessels passing or meeting close together, which can cause them to be drawn together and to sheer. The effect grows with speed and in confined water.

The point about which a vessel appears to rotate when turning, roughly one-quarter to one-third of the length from the bow when moving ahead. Its position shifts with speed and trim.

The path traced by a reference point during a turn, described by tactical diameter and advance. It is used to plan manoeuvres and assess the space needed to alter course or avoid a hazard.

The speed at which a vessel can take proper and effective action to stop or avoid a collision, considering visibility, traffic, manoeuvrability and background light. It is a continuous judgement, not a fixed number.

Continuous watch by sight and hearing and by all available means to appraise the situation and detect risk of collision. It must be maintained in all conditions, including by radar and VHF where appropriate.

A situation where a vessel's approach to another creates danger, judged from a steady bearing and decreasing range. When in doubt, the risk is deemed to exist and action must be taken in good time.

The vessel required to keep out of the way of another under the steering and sailing rules. It must take early and substantial action, avoiding crossing ahead where practicable.

The vessel that keeps its course and speed while another must keep clear, but which must take action when the give-way vessel fails to do so. It may not alter course to port for a vessel on its own port side.

A channel where a vessel must keep as near to the outer limit on its starboard side as is safe and practicable. It imposes restrictions on overtaking, crossing and anchoring.

The coordinated use of all bridge personnel, information and equipment through clear communication, task sharing and challenge. It reduces single-person error and is a core element of accident prevention.

A message pattern in which the receiver repeats the instruction back and the sender confirms it was heard correctly. It prevents misunderstandings during manoeuvring and emergency response.

The perceived difference in rank or expertise that discourages junior crew from speaking up. A steep gradient suppresses challenge and increases the risk of unchallenged error on the bridge.

Planning of hours of work and rest, watch patterns and crew levels to keep performance within safe limits. It addresses cumulative sleep loss, circadian disruption and workload, and is a regulatory requirement.

A flag State document specifying the minimum number and qualifications of crew needed for safe operation. The actual manning must be at least equal to it, with evidence retained on board.

A record of a ship's identity, ownership and management history, kept on board and issued by the flag State. It supports transparency and port State control checks.

Inspection of foreign ships in a port to verify compliance with international conventions. Detainable deficiencies can stop a vessel from sailing until they are rectified.

The documented procedures, responsibilities and resources required by the ISM Code to ensure safe operation and pollution prevention. It includes emergency preparedness, reporting and internal audit.

The document assigning each person on board a station and duties in an emergency, with signals and procedures. It must be displayed and kept current, and crew must be familiar with it.

Prepared procedures and checklists for events such as fire, flooding, collision, pollution and abandoning ship, with defined roles and communication lines. Drills test its effectiveness.

The IMO code requiring shipping companies to operate a safety management system, with designated persons ashore and documented procedures. It applies to most commercial ships and is verified by certification.

The shipper's document identifying a dangerous consignment by proper shipping name, UN number, class, packing group and quantity. It is the basis for stowage, segregation and emergency planning.

The IMO code governing classification, packing, marking, labelling, stowage and segregation of packaged dangerous goods by sea. It is given effect through SOLAS chapter VII.

A matrix in the IMDG Code specifying the required separation between incompatible dangerous goods, from away from to separated by a complete compartment. It is applied together with stowage requirements.

A document evidencing receipt of goods for carriage, acting as a contract of carriage and, when negotiable, as a document of title. Its statements on quantity and condition carry legal weight.

An international convention allocating liability between carrier and cargo interests, setting carrier duties and defences and package limitation amounts. It applies by incorporation in the bill of lading.

A principle requiring cargo, ship and freight to share a loss or expense deliberately incurred to save the venture from a common peril. It is adjusted by average adjusters and secured by bonds.

A contract to carry goods on a specified voyage for freight calculated per ton of cargo, with laytime and demurrage terms. The owner retains commercial operation of the ship.

A contract hiring the ship for a period at a daily rate, with the charterer directing employment while the owner keeps possession and management. Off-hire and performance clauses are central.

Liquidated damages payable by the charterer when loading or discharging exceeds the allowed laytime. It compensates the owner for detention of the vessel.