BD Deck Officer Class 2 (Chief Mate) key terms

A method of ocean navigation following the shortest path between two positions on the Earth's surface. The track appears curved on a Mercator chart, so course and distance are recalculated at intervals.

A track that crosses every meridian at the same angle, shown as a straight line on a Mercator chart. It is longer than a great circle but allows a constant course to be steered.

A celestial fix technique comparing the observed altitude of a body with the altitude calculated for an assumed position. The difference, the intercept, is plotted along the azimuth to give a position line.

Chart datum is the reference level, normally lowest astronomical tide, from which depths are measured; a drying height is the height of a feature above that level, shown differently from a depth.

A berth-to-berth plan produced by the bridge team covering appraisal, planning, execution and monitoring, including hazards, no-go areas, abort points, under-keel clearance, contingency anchorages and position-fixing intervals.

A radar monitoring technique in which a line parallel to the intended ground track is set on the display. A steady distance between a fixed echo and that line confirms the ship is on track.

Set is the direction towards which a current flows and drift is its speed. They are found by comparing the dead reckoning position with a reliable fix, then applied to course and speed.

The volume in cubic metres occupied by one tonne of a cargo in its shipped condition, including unavoidable space. It allows the space needed for a given weight of cargo to be calculated.

The volume of a cargo space that cannot be filled because of hold shape, obstructions or packaging. It is expressed as a percentage and deducted from the hold's nominal capacity.

Condensation on the cargo surface is cargo sweat; condensation on the ship's structure is ship sweat. Each indicates whether outside air should be admitted or excluded during ventilation.

The highest moisture content at which a solid bulk cargo is accepted for shipment without significant risk of liquefaction. It is established by laboratory test and compared with the actual moisture content.

A calculation of cargo weight from draught readings before and after loading, corrected for displacement, trim, water density, ballast, fuel, stores and constant, used to check quantities for the bill of lading.

The vertical distance from the centre of gravity to the transverse metacentre. It measures initial stability: small values produce a tender, slow roll, large values a stiff, uncomfortable roll.

The virtual rise of a ship's centre of gravity caused by liquid moving freely in a partly filled tank, which reduces metacentric height and can endanger stability if several tanks are slack.

A heel angle at which a ship with initially negative metacentric height settles, either to port or starboard. It is corrected by lowering the centre of gravity, not by transferring weight across.

A graph of righting lever GZ against heel angle for a given displacement and centre of gravity. It shows maximum GZ and range of stability and is used to check intact stability criteria.

Vertical forces and resulting bending loads along the hull, produced by uneven distribution of weight and buoyancy. Excessive values cause hogging, sagging, buckling or structural cracking.

The assessment of a ship's ability to survive with compartments flooded. Permeability is the proportion of a compartment's volume that water can fill, allowing for machinery, structure and cargo.

The International Safety Management Code requires companies and ships to run a documented safety management system covering policy, risk assessment, procedures, training, emergency preparedness, maintenance and internal audit.

A signed authorisation for high-risk work such as hot work, enclosed-space entry or working aloft, confirming that hazards have been assessed, controls applied and the area made safe.

Fatigue is the physical and mental impairment caused by inadequate sleep, long hours or disturbed rest. STCW sets minimum rest hours and requires records to limit its effect on watchkeepers.

A document issued by the carrier acknowledging the goods shipped, evidencing the contract of carriage and acting as a document of title. In a third party's hands it is conclusive evidence of shipment.

A maritime law principle under which extraordinary sacrifice or expenditure intentionally made to save ship and cargo from a common peril is shared proportionally by the property owners saved.

The part of the MARPOL Convention dealing with pollution by oil. It regulates discharges, requires the Oil Record Book and sets construction and equipment standards for tankers.

The International Ship and Port Facility Security Code requires security officers, ship and port facility security plans, access control, drills and defined security levels to deter unlawful acts against ships.

A model of combustion requiring fuel, oxygen, heat and an uninhibited chemical chain reaction. Extinguishing methods work by removing one or more of these four elements.

Cooling compartments and structures adjacent to a fire with water spray to limit conduction and radiant heat spread, while avoiding unnecessary water accumulation that would reduce stability.

A posted document assigning every person on board a station and specific duty for fire, abandon-ship, man-overboard or other emergencies, with named substitutes for key roles.

Sea areas A1 to A4 classify waters by the radio services available, from VHF coast-station coverage through MF and Inmarsat to polar regions, and determine the equipment a ship must carry.

A terrestrial system that automatically receives and prints navigational warnings, meteorological forecasts and search and rescue information broadcast on 518 kHz in English within coastal range.

An emergency position-indicating radio beacon that, when activated, transmits a distress alert with the vessel's identity and position through the COSPAS-SARSAT satellite system to rescue coordination centres.

A depth selected in ECDIS that separates safe from unsafe water. Areas shallower than the contour are highlighted and alarms warn of the vessel's predicted position crossing into them.

An intense warm-core low-pressure system over tropical oceans with organised convection, heavy rain and destructive winds around a calm centre; avoidance requires forecasting its track and keeping clear of dangerous quadrants.

With your back to the wind in the Northern Hemisphere, low pressure lies to your left, and to your right in the Southern Hemisphere; used to estimate the bearing of a depression.

An abnormal rise of sea level near a coast caused by strong onshore winds and low atmospheric pressure, which can reduce charted depths, flood harbours and affect pilot boarding and berthing.

The minimum vertical distance between keel and seabed, allowing for squat, tide, swell, chart accuracy and heel. It is calculated for each leg of a passage through restricted or shallow water.

The coordinated use of bridge personnel, equipment and information to conduct a safe passage, emphasising clear communication, workload sharing, monitoring and the obligation to challenge unsafe decisions.

A discussion between master and pilot before an arrival or departure covering the ship's manoeuvring characteristics, the passage plan, tugs, berthing arrangements, local conditions and emergency contingencies.

The increase in draught and reduction in under-keel clearance caused by interaction between a moving hull and the seabed, greatest in shallow water and at high speed.

The collision regulation for restricted visibility, requiring a safe speed, proper lookout, radar use, and avoidance of altering course to port for a vessel forward of the beam.