BD Deck Officer Class 1 (Master) key terms

A method of estimating a vessel's position by advancing the last known position using course steered and speed through the water, without correcting for wind or current.

The most probable position derived from a dead reckoning position corrected for the estimated effects of wind (leeway) and current (set and drift).

The direction toward which a current flows (set) and its speed (drift), expressed as a vector used to convert a course steered into a course and speed made good.

The actual direction of travel over the ground achieved by a vessel after the combined effects of heading, leeway, and current are taken into account.

The distance at which a light of given luminous intensity produces an illuminance of 2×10⁻⁷ lux at the observer's eye, used to compute a light's nominal range in clear air.

The distance at which a navigational light is visible in clear air with a meteorological visibility of 10 nautical miles, published on charts and in light lists.

The distance a light can actually be seen for the prevailing meteorological visibility, obtained from the nominal range using a luminous range diagram.

The distance at which a light becomes visible over the horizon due to the curvature of the earth, calculated from the heights of eye and light using dip and distance-to-horizon tables.

The angular depression of the visible sea horizon below the true horizontal, increasing with height of eye and reduced by atmospheric refraction, applied as a correction to sextant altitudes.

The residual error of a sextant when the horizon and its reflected image are made coincident with the instrument reading zero, determined by observing the horizon and corrected before sight reduction.

A sight reduction technique plotting a calculated position, drawing the azimuth line, and laying off the intercept difference between observed and calculated altitudes to obtain a position line.

The vertical distance between the centre of gravity and the initial transverse metacentre of a ship; a positive value indicates initial stability in the upright condition.

The horizontal distance between the centre of gravity and the vertical through the centre of buoyancy at a given heel angle, producing the moment that returns a heeled ship upright.

The apparent rise in a ship's centre of gravity caused by liquid shifting in partially filled tanks as the vessel heels, reducing metacentric height and stability.

The angle of heel at which a ship with negative initial metacentric height comes to rest, where the righting lever curve crosses the axis with zero initial slope.

The permanent mark amidships indicating the maximum permitted draught under the International Convention on Load Lines, with seasonal, fresh water, and timber allowances shown on the load line disc.

The total weight a ship can carry when loaded to her permitted load line, comprising cargo, fuel, fresh water, ballast, stores, crew and effects.

The ratio of the underwater volume of a ship's hull to the volume of a rectangular block of the same length, breadth and draught, used to estimate displacement and powering.

Internal longitudinal loads arising from the difference between weight and buoyancy distribution along the hull, causing hogging or sagging and checked against permitted limits.

Longitudinal hull deformation where hogging means excessive buoyancy amidships with ends drooping, and sagging means excessive weight amidships with the ends supported.

A twisting moment on the hull caused by uneven loading across the beam, such as heavy cargo on one side or in a forward corner, producing racking stresses on transverse structures.

The temperature to which moist air must be cooled at constant pressure for it to become saturated, so that further cooling produces condensation, fog, or dew.

The ratio of the actual water vapour content of air to the maximum it could hold at that temperature, expressed as a percentage and indicating proximity to saturation.

Suspension of water droplets near the sea surface reducing visibility below one kilometre, formed by cooling air to its dew point or by mixing moist air masses.

An intense low-pressure cyclonic system over tropical oceans with a calm eye, rotating winds, and a dangerous semicircle; vessels avoid the storm centre and track.

Tactical manoeuvring to keep clear of a tropical cyclone's path and dangerous quadrant, using the 1-2-3 rule and altering course to increase distance from the centre.

Long-period waves that have propagated away from their generating wind area, producing regular undulations that can affect vessel motion and surf conditions far from the storm.

A flag State certificate specifying the minimum number and qualifications of personnel required to operate a ship safely, forming the basis for watchkeeping arrangements.

A posted schedule assigning each crew member specific emergency duties and stations, including abandon-ship, fire, and man-overboard responses, and reviewed at drills.

A float-free satellite beacon activated automatically on immersion or manually in distress, transmitting identification and position to the COSPAS-SARSAT system for search and rescue.

The international radio-communications system using satellite and terrestrial equipment for distress alerting, search and rescue coordination, and dissemination of safety information at sea.

An automated VHF, MF, and HF radio function that transmits preformatted distress, urgency, safety, and routine alerts with vessel identification to selected stations.

Shipboard equipment using gravity separation and coalescing filters to reduce the oil content of bilge water to not more than 15 parts per million before overboard discharge.

A mandatory record of all oil transfer, ballasting, cleaning, and disposal operations on board, open to inspection by port State control officers and flag State surveyors.

The chapter of the International Convention for the Prevention of Pollution from Ships governing prevention of pollution by oil, including discharge criteria and equipment requirements.

Inspection by a coastal State of foreign-flagged ships in its ports to verify compliance with international conventions, with authority to detain ships for serious deficiencies.

The State whose nationality a ship holds, responsible for surveying, certifying, and enforcing international convention requirements on vessels flying its flag.

The effective management and utilisation of all available resources, including personnel, equipment, and information, on the bridge to promote safe and efficient passage.

A continuous, accurate perception and understanding of what is happening around the vessel, including traffic, weather, and own-ship state, enabling timely and correct decisions.

A structured and documented system required by the ISM Code, covering safety and environmental policy, procedures, responsibilities, and continuous improvement on board.