MARINA OIC-NW Theoretical Exam key terms

The position obtained by advancing the last known fix using only the vessel's course and speed through the water, ignoring wind and current. It is an estimate, not a fix, and should be updated frequently.

The best position estimate derived from dead reckoning with an allowance applied for leeway, current and tidal stream. It is plotted with a distinctive symbol and is more realistic than a raw DR position.

A position confirmed by observation of external objects or signals, for example two or more visual bearings, a radar range and bearing, or a satellite position. It is plotted with a circle and time.

The direction towards which a current or tidal stream flows (set) and its speed (drift). Both are needed to convert a course steered into a course and speed made good over the ground.

The actual direction of travel over the ground after combining the vessel's heading, leeway and the effect of current. It differs from the course steered and is used in passage planning and position monitoring.

A line of position obtained by observing two charted objects that appear in line, such as leading marks, a headland and a buoy. It gives a very accurate position line without a compass bearing.

A locus of points where the vessel must lie, derived from a single observation such as a bearing, range or sounding. Two or more intersecting lines of position produce a fix.

The speed at which a vessel can take proper and effective action to avoid collision and stop within a distance appropriate to the prevailing circumstances, including visibility, traffic density, draft and background light.

A situation where a vessel's approach may lead to collision, presumed to exist if the compass bearing of an approaching vessel does not appreciably change. Positive action must be taken early and substantially.

The vessel required to keep out of the way of another under the steering and sailing rules. It must take early and substantial action and, where possible, avoid crossing ahead of the stand-on vessel.

The vessel with the right of way under the steering and sailing rules. It must keep its course and speed but may take action to avoid collision as soon as it becomes apparent the give-way vessel is not acting.

A navigable waterway of restricted width, such as a dredged channel or river. Vessels must keep to the starboard side of the channel and avoid anchoring or crossing unnecessarily.

A routing measure established to separate opposing streams of traffic using traffic lanes, separation zones or lines. Vessels must proceed in the general direction of the lane and avoid crossing the separation zone.

Any condition in which visibility is reduced by fog, mist, snow, rain or dust. Vessels must use radar, reduce speed, sound fog signals and post a proper lookout by sight and hearing.

A competent person stationed to watch by sight and hearing, and by all available means, so as to fully appraise the situation. The lookout must report hazards and must not be given duties that interfere with the watch.

A detailed plan from berth to berth covering intended track, waypoints, abort points, safe speeds, tidal windows, contingency anchorages and chart corrections. It is prepared, checked and approved before departure.

The vertical distance between the lowest point of the hull and the seabed. It must account for squat, tide, swell, heel and charted depth accuracy, and is a key input to passage planning.

The reduction of under-keel clearance and change of trim caused by water flow around a moving hull. It increases with speed and in shallow water or narrow channels, and is greatest for full-form vessels.

The tendency of a vessel in shallow or confined water to be drawn towards the nearer bank and to turn away at the bow, caused by asymmetric water pressure around the hull. It is strongest at close range and higher speed.

The point about which a vessel appears to rotate during a turn. When moving ahead it lies well forward of midships; when going astern it moves aft, which explains the behaviour of the stern in manoeuvres.

The sideways force produced by the propeller, especially when going astern, caused by blade asymmetry and paddle-wheel effect. It can be used deliberately when berthing or turning in a narrow basin.

The loss of effective transverse stability caused by liquid moving freely in a partly filled tank or compartment. It raises the virtual centre of gravity and reduces metacentric height, and is reduced by subdivision.

The vertical distance between the centre of gravity and the transverse metacentre. A small positive GM gives a stiff, tender or lively ship; a negative GM indicates an unstable condition.

The volume of watertight hull above the waterline that can be flooded before the vessel sinks. It is expressed as a percentage of total volume and is protected by watertight subdivision and closing appliances.

The Plimsoll mark showing the maximum permitted draft in different seasons and water densities. It is assigned under the Load Line Convention and must not be submerged when the vessel sails.

A method of determining the weight of cargo loaded or discharged by measuring the vessel's fore, aft and midship drafts and applying hydrostatic corrections. It is used for bulk cargo quantity disputes.

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

The required physical separation of incompatible dangerous goods, for example away from, separated from or separated by a complete compartment. It is set out in the IMDG Code and shown on the dangerous goods manifest.

A document giving the hazards, handling, first-aid and firefighting information for a hazardous substance. It must be available to the crew for any dangerous goods carried or used on board.

The annex of the pollution convention covering prevention of pollution by oil. It regulates oily water discharges, the oil record book and the shipboard oil pollution emergency plan.

A statutory record of all oil transfer, ballasting, cleaning and discharge operations on board. Entries must be made promptly, signed by the officer in charge and kept available for inspection.

A statutory log of garbage handling and discharge operations, required under MARPOL Annex V for most vessels. Each entry states the category, estimated amount, date, time and position of discharge or incineration.

The Global Maritime Distress and Safety System, a worldwide network of satellite and terrestrial communications for distress alerting, search and rescue coordination and maritime safety information. Its carriage requirements depend on sea area.

A digital selective calling distress alert transmitted on VHF channel 70 or an MF/HF distress frequency. It carries the vessel identity and nature of distress and should be followed by a voice mayday on channel 16.

An emergency position-indicating radio beacon that transmits a distress signal with the vessel identity to the COSPAS-SARSAT satellite system. It should float free and activate automatically if the vessel sinks.

An electronic chart display and information system that meets IMO performance standards and may replace paper charts. It shows the vessel's position on an electronic navigational chart and gives safety contour and route alarms.

In ECDIS, a user-selected depth that separates safe from unsafe water and triggers alarms when the vessel's safety domain crosses it. It should be set with allowance for draft, squat and chart accuracy.

Automatic radar plotting aid, which acquires targets and computes their course, speed, closest point of approach and time to closest approach. ARPA output is an aid to, not a substitute for, visual assessment.

Closest point of approach and time to closest point of approach, used to judge whether a target will pass safely. Limits are set by the officer of the watch and alarms sound when a target is predicted to breach them.

An area behind a mast, funnel or other obstruction where radar echoes are weak or absent. The watchkeeper must know its extent and use visual lookout or a second scanner to cover it.

Standard names for lines such as head line, stern line, breast line and spring, identified by the direction in which they restrain the vessel. Correct terminology prevents confusion during berthing and unberthing.

The inboard end of a rope or wire that is secured to the vessel, for example the end of a mooring line made fast in a locker. It must be secured so the line cannot run out under load.

A fitting such as a roller, panama lead or chock that guides a rope or wire in a safe direction and reduces chafe. Lines should be led through fairleads that give a straight lead to the winch or bollard.

The watch kept while at anchor to monitor the vessel's position, the anchor bearing and distance, and the approach of other vessels. It includes checking the holding ground and readiness of the main engine.

The planning of a route and speed to avoid adverse weather and use favourable conditions, based on forecasts and ship response. It reduces fuel consumption, cargo damage and the risk of heavy weather damage.

A weather map showing isobars, fronts, pressure centres and their movement at a stated time. Close isobars indicate strong wind, and the spacing and shape reveal the likely wind direction and changes.

A numerical scale from 0 to 12 describing wind strength by its observable effect on the sea surface and on a vessel. It is used in weather reports and for deciding when to reduce speed or alter course.