Greece Category A Theory key terms

The direction of an object measured in degrees clockwise from true north, used in chartwork to plot a vessel's position or intended course without magnetic interference.

The angular difference at a given place between true north and magnetic north, shown on the chart and applied when converting compass readings to true directions.

The error in a magnetic compass caused by the vessel's own magnetic fields and electronics, varying with heading and recorded on a deviation table for correction.

A line drawn on a chart from a known landmark along a measured bearing, used with a second line to fix the vessel's position by intersection.

A confirmed location on the chart obtained by crossing two or more position lines, such as bearings, ranges or GPS coordinates, at the same time.

An estimated position calculated from the last known fix by applying course and speed through the water, ignoring wind and current effects.

The best possible position estimate obtained by adjusting a dead reckoning plot for the effects of leeway and tidal stream, shown with a square symbol.

The horizontal movement of water caused by the rise and fall of the tide, expressed as a set (direction) and drift (rate), which must be allowed for in passage planning.

The sideways drift of a vessel downwind of its heading, caused by wind acting on the hull and superstructure, which must be added to the course steered.

The heading a navigator must hold to make good a desired track over the ground after allowing for tidal stream and leeway, found by vector triangle.

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 and visibility.

A situation where there is doubt whether a close-quarters situation is developing; assessed by watching for a steady bearing and decreasing range of an approaching vessel.

The vessel required to keep out of the way of another under the steering and sailing rules, taking early and substantial action to keep well clear.

The vessel with the right of way that must keep its course and speed, but may take action to avoid collision if the give-way vessel fails to do so.

Continuous visual and auditory watch kept by sight and hearing as well as by all available means, so that a full appraisal of the situation can be made.

Any condition in which visibility is reduced by fog, mist, snow, rain or other causes, requiring reduced speed, sound signals and ready engines under the rules.

Prescribed sound signal sounded in or near restricted visibility, such as one prolonged blast at intervals for a power-driven vessel making way through the water.

A numerical 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.

A forecast warning of winds of force 8 or above on the Beaufort scale, typically indicating conditions hazardous to small craft and requiring shelter or route change.

A description of the condition of the sea surface in terms of wave height and character, usually given by a code number in marine forecasts.

Long, regular waves that have travelled far from the weather system that generated them, often arriving with little local wind and affecting comfort and safety.

A line on a weather chart joining places of equal atmospheric pressure; closely spaced isobars indicate strong winds and a steep pressure gradient.

The leading edge of an advancing mass of cold air, often bringing a band of heavy showers, squalls and a wind shift as it passes over a vessel.

A sudden, sharp increase in wind speed, often with rain, lasting minutes, which can knock down or overpower a small vessel if not anticipated.

The arrangement of lines and anchors securing a vessel to a quay, pontoon or buoy, including the selection of appropriate ropes, springs and fenders.

A mooring rope led fore and aft along the vessel to prevent it from moving ahead or astern along the berth when machinery or wind pushes it.

A cushion, usually of rubber or woven rope, hung over the side to protect the hull from chafing against a quay, pontoon or another vessel.

Reducing the area of sail by folding or rolling part of it away, done to keep the vessel balanced and controllable as wind strength increases.

A manoeuvre in which sails are set to oppose each other so the vessel lies nearly stopped and drifts slowly, used to ride out weather or take a rest.

An emergency in which a person falls into the water; the immediate response is to shout, throw buoyancy, mark the position and manoeuvre the vessel for recovery.

The licence issued by the flag state confirming that the holder has met the training and examination requirements to act as skipper of a vessel of a specified category.

The country whose flag a vessel flies, which has jurisdiction over it and is responsible for its registration, survey and crewing standards.

Inspection of foreign vessels visiting a port by the local authorities to verify that the vessel and its crew comply with international safety and pollution conventions.

The master's overall legal duty for the safety of the vessel, crew and passengers, including passage planning, crew competence, and compliance with regulations.

The international spoken distress signal used only when a vessel or person is in grave and imminent danger and immediate assistance is required.

The international urgency signal used when a vessel has a serious problem but is not in immediate danger of loss, such as engine failure without risk to life.

A ring-shaped flotation device carried on deck and thrown to a person in the water, often fitted with a light and line to mark the position.

The three elements needed for combustion: fuel, oxygen and heat; firefighting works by removing at least one of these to break the triangle.

A portable device that discharges a suppressant such as powder, foam or CO2 onto a fire, chosen to suit the class of fire and used with the correct technique.

A remote valve or lever that stops the supply of fuel to the engine, used as the first action in an engine-room fire to remove fuel from the fire triangle.

The rotating rubber or plastic vaned component inside a sea-water pump that moves cooling water through the engine; worn vanes cause overheating and must be checked.

The circuit that circulates sea water and coolant through the engine to remove heat, comprising the raw-water pump, heat exchanger or jacket and the exhaust injection point.

A condition where engine temperature rises above normal, commonly caused by a blocked intake, failed impeller or low coolant, and which can quickly cause serious damage.

A zinc or aluminium block bolted to the hull, shaft or outdrive that corrodes in preference to the metal parts it protects against galvanic action.

Electrochemical damage occurring when two different metals are immersed in seawater and electrically connected, causing the less noble metal to dissolve.

The practice of electrically connecting underwater metal fittings to a common point so that they share the same potential and anodes protect them all.

A heavy-duty switch that disconnects the battery from the vessel's electrical circuits, used to prevent discharge and reduce fire risk when leaving the boat.

A protective device containing a wire that melts and breaks the circuit when current exceeds its rating, safeguarding wiring and equipment from overload.

The amount of electrical charge a battery can deliver, usually stated in ampere-hours, indicating how long it can supply a given current before needing recharge.