ENSH Access Contest key terms

International treaty rules that set steering, sailing and light-and-shape requirements so vessels avoid collision; they define right-of-way, overtaking, head-on and crossing situations and apply to all vessels on the high seas and connected waters.

Official document issued by a national authority confirming that the holder meets the training, sea-service and examination requirements for a stated grade, such as boatmaster or skipper, and is therefore authorised to command the vessels described on it.

The smallest number and qualification mix of crew that a flag administration decides is needed to operate a vessel safely, covering navigation, machinery, radio watch and emergency duties at all times.

Inspection of foreign-flagged ships in a national port to check compliance with international conventions; inspectors may detain a ship whose deficiencies pose a risk to safety, health or the environment.

Formal prohibition by a port authority preventing a vessel from sailing until listed deficiencies are corrected, issued when the ship is judged unseaworthy or a danger to persons, property or the marine environment.

Spoken distress signal used only when a vessel or person faces grave and imminent danger and immediate assistance is required; it has absolute priority over all other radio traffic and is sent on VHF channel 16 or a distress frequency.

Spoken urgency signal announcing a serious situation that threatens safety but is not yet an immediate distress, such as engine failure or a medical problem, and which requires assistance or advice without distress priority.

Spoken safety signal that introduces an important navigational or meteorological warning, for example a drifting hazard, a broken light or a gale forecast, transmitted so other stations can take note.

Digital Selective Calling transmission, usually on VHF channel 70, that automatically sends the vessel's identity and position to alert rescue authorities and other stations before voice contact is established on a working channel.

Nine-digit Maritime Mobile Service Identity number programmed into a vessel's radio equipment; it uniquely identifies the station in digital calls and is entered automatically in distress alerts so rescuers know which vessel is calling.

Short test transmission, normally on a low-power channel or with a coast station, confirming that a radiotelephone can transmit and receive clearly; it must not be made on the distress and calling channel.

The horizontal reference level from which depths printed on a nautical chart and the heights of drying features are measured, usually a low-water level chosen so that actual depth is rarely less than charted.

Water depth shown on a nautical chart, measured below chart datum and printed as a number; the real depth at any moment is this figure plus the height of tide at that place and time.

Vertical distance between chart datum and the actual sea surface at a given place and time, found from tide tables, tide curves or a tide gauge, and added to charted depths to obtain true depth.

Margin of water between the lowest point of a vessel's hull and the seabed; it must always remain positive and is calculated from charted depth, height of tide, squat and expected swell.

Reduction of under-keel clearance caused by a vessel moving through shallow water, which lowers water pressure around the hull and makes the ship sink bodily and trim by the bow or stern.

Changes in a vessel's behaviour when depth is small compared with draught: increased squat, greater turning circle, stronger bow wave, reduced speed and a tendency to sheer, all of which require reduced speed and careful steering.

The direction towards which a tidal stream or current carries a vessel, called the set, together with the distance it moves the vessel in a given time, called the drift; both must be allowed for in passage planning.

The actual direction of travel of a vessel over the seabed, which differs from the heading steered whenever wind, waves or current push the vessel sideways; it is shown by GPS and plotted on the chart.

Estimation of a vessel's position by advancing the last known fix with the courses steered and speeds through the water, without correcting for current; it drifts from the true track as errors accumulate.

Numbered scale from 0 to 12 describing wind strength by its observable effects on the sea surface and on a vessel, used in weather reports and forecasts to communicate wind force without instruments.

Official forecast bulletin announcing mean wind speeds of force 8 or more, or gusts of similar strength, issued so mariners can seek shelter, reduce sail or alter plans before conditions become dangerous.

Description of the roughness of the sea surface, usually given by wave height and a code number, reflecting the combined effect of wind waves and swell at a particular place and time.

Long, regular waves that have travelled far from the weather system that generated them; they can arrive in calm local conditions and cause heavy rolling or surf at an exposed bar or inlet.

Message issued by a hydrographic or coastguard authority reporting a temporary hazard or change to charted information, such as a moved buoy, a new wreck or a closed channel, so mariners can amend their plans.

Periodic publication listing corrections and updates to charts and nautical publications, including new hazards and changed aids to navigation, which the navigator applies by hand to keep charts current.

In a crossing situation, the vessel that must keep out of the way of the other by taking early and substantial action, normally passing astern of the stand-on vessel and avoiding crossing ahead of it.

Vessel that must keep her course and speed in a crossing situation while the give-way vessel manoeuvres; she may act to avoid collision only when it becomes clear the other vessel is not taking proper action.

Speed at which a vessel can take proper and effective action to stop within a safe distance and avoid collision, judged from visibility, traffic density, draught, sea state and stopping distance.

Item of wearable buoyancy equipment, such as a lifejacket or buoyancy aid, that keeps a person's head above water; it must be the right size, in good condition and worn when conditions or duties warrant.

Emergency position-indicating radio beacon that, when activated manually or by immersion, transmits a distress signal via satellite to rescue coordination centres, giving the vessel's identity and, in modern units, its position.

Emergency in which a person falls into the water; the response is to shout the alarm, throw buoyant equipment, mark the position, turn the vessel back and keep the person in sight while recovering them.

Recovery manoeuvre that brings a vessel back along its original track after a person falls overboard: helm hard over one way, then hard the other way once heading has changed by about 60 degrees.

Document posted aboard ship assigning each crew member a specific station and duty for emergencies such as fire, collision, flooding or abandon ship, and naming the signals that call everyone to stations.

Documented set of procedures, responsibilities and checks a vessel operator maintains to ensure safe operation and pollution prevention, following the ISM Code where it applies, and subject to audit and inspection.

International convention controlling pollution from ships through annexes covering oil, noxious liquids, harmful packaged goods, sewage, garbage and air emissions, each with discharge limits and record-keeping requirements.

Written plan required on larger vessels describing how waste is collected, separated, stored, processed and discharged, naming the person in charge and the procedures that keep discharges within MARPOL limits.

Sea region designated under MARPOL where stricter discharge rules apply because of its ecological, oceanographic or traffic conditions, so garbage, sewage or oily water may be discharged only under tighter limits or not at all.

Mandatory log in which oil tankers and larger machinery vessels record every transfer, discharge and disposal of oily residues, allowing inspectors to verify that oil has not been illegally released into the sea.