SAMSA Skipper Category C (Coastal, up to 15 nm) Exam (South Africa) key terms

A method of estimating a vessel's present position by advancing a known starting position using course steered, speed through the water and time run, without reference to outside landmarks or fixes.

A confirmed position obtained from external references such as bearings to landmarks, GPS, or celestial observations, used to check and correct the dead reckoning plot.

Two charted objects seen in line, one behind the other, forming a position line along which the vessel lies; often used to clear hazards or confirm a leading line.

The direction of an object from the vessel, expressed in degrees relative to north (true or magnetic); used to plot position lines on a chart.

The angular difference between true north and magnetic north at a given place, shown on the chart with its annual rate of change; applied when converting between magnetic and true courses.

The error in a magnetic compass caused by the vessel's own magnetic fields and electronics, varying with heading; recorded on a deviation card and applied after variation.

The coordinate system for positions on Earth: latitude measured north or south of the equator in degrees up to 90, longitude measured east or west of the prime meridian up to 180.

The reference level from which depths and drying heights on a nautical chart are measured, normally a low water level chosen so that the charted depths are mostly greater than actual depths.

The depth of water shown on a chart, measured from chart datum, which must be added to the predicted height of tide to find the actual depth at a given time.

The vertical distance of the sea surface above chart datum at a particular time and place, taken from tide tables or predictions and added to charted depths.

A tide of large range occurring near new and full moon when the sun and moon align, producing higher high waters and lower low waters than average.

A tide of small range occurring near the first and third quarters of the moon when the sun and moon act at right angles, producing lower high waters and higher low waters.

The vertical difference between consecutive high water and low water levels at a place; used with charted depth to judge safe water and anchoring scope.

A rough method of estimating tide height between high and low water by dividing the total range into twelfths, with the flow changing fastest in the middle hours of the tide.

The direction (set) and speed (drift) in which a tidal stream or current carries a vessel over the ground, used to calculate a course to steer to make good a desired track.

The horizontal movement of water caused by the rise and fall of the tide, usually reversing direction through a cycle and shown on charts and in tidal stream atlases.

The brief period around high or low water when the tidal stream is weakest or has stopped before reversing direction; often the easiest time to enter or leave a berth.

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

An area of lower atmospheric pressure around which winds circulate; in the southern hemisphere they blow clockwise, bringing unsettled or stormy weather and rising winds as pressure falls.

The boundary between two air masses of different temperature and humidity; passage of a cold or warm front typically brings a wind shift, cloud, rain and change in visibility.

A scale from 0 to 12 describing wind strength by its observable effects on sea state and, on land, on trees and smoke; used in forecasts to judge conditions.

A local daytime wind blowing from sea to land caused by the land heating faster than the water; it can strengthen or oppose the prevailing wind and often reverses at night.

A sudden, brief increase in wind speed, often with a change in direction, rain or thunder; a sign of unstable air that requires prompt reduction of sail or speed.

A South African weather warning issued when winds or sea conditions are expected to become hazardous to small vessels; skippers should avoid or curtail sea passages.

In a crossing or overtaking situation, the vessel required to keep out of the way of the other by taking early and substantial action, avoiding crossing ahead.

The vessel required to maintain course and speed in a crossing or overtaking situation, while keeping a proper lookout and taking action if the give-way vessel does not.

The speed at which a vessel can take proper and effective action to avoid collision and stop within a distance appropriate to the prevailing visibility, traffic, sea state and manoeuvrability.

A white light showing forward over an arc of 225 degrees, carried on the fore-and-aft centreline of a power-driven vessel underway; larger vessels show two, one above the other.

A red light on the port side and a green light on the starboard side, each showing over an arc of 112.5 degrees from ahead to just abaft the beam.

A white light showing aft over an arc of 135 degrees, placed as near the stern as practicable, used at night to identify a vessel's heading.

A signal made with a whistle or horn, such as one short blast meaning altering to starboard or two meaning altering to port, used to indicate manoeuvres and in restricted visibility.

Any condition such as fog, mist, snow or heavy rain that reduces visibility; vessels must proceed at a safe speed, sound appropriate signals and post a proper lookout.

Buoys marking the sides of a navigable channel: port-hand marks are red and can-shaped, starboard-hand marks are green and conical, following the direction of buoyage.

A buoy indicating the safe direction of navigable water by its compass point: north (black over yellow), east, south and west marks, with topmarks and light rhythms matching the direction.

A red and white vertically striped buoy with a red sphere topmark, marking mid-channel or a landfall where there is navigable water all around.

A black buoy with a red horizontal band and two black spheres as topmark, placed over a hazard with navigable water all around it.

The length of anchor chain or rope paid out relative to water depth, commonly about five to seven times depth for rope, to give a shallow angle and secure holding.

The circle a vessel describes around its anchor as wind and tide change, determined by the total length of anchor rode and the vessel's length; it must be clear of other boats and hazards.

A watch kept while at anchor to check that the vessel is not dragging, that the anchor bearing and nearby landmarks stay constant, and to summon help if the anchor drags.

A quick, secure knot for tying a line to a cleat, made by taking a full turn around the base, then figure-eight turns over the horns, finished with a locking hitch.

A knot forming a fixed loop at the end of a line that will not slip and is easily untied; used for mooring, attaching sheets and recovering a person overboard.

A mooring line led fore or aft from a vessel to the dock to prevent it moving along the berth; bow and stern springs are set in opposite directions.

The international distress signal, spoken three times on VHF channel 16, used only when a vessel or person is in grave and imminent danger and immediate assistance is needed.

The urgency signal, spoken three times on VHF channel 16, used when a vessel or person is in trouble but not in immediate danger and assistance may be needed.

The safety signal, spoken three times on VHF channel 16, used to announce an important navigational or weather warning such as a navigational hazard or gale warning.

Digital Selective Calling, a VHF radio feature that sends an automated distress alert with the vessel's identity and position, after which voice communication is made on channel 16.

Emergency Position Indicating Radio Beacon, a float-free device that transmits a distress signal to satellite systems when activated, giving the vessel's identity and position to rescue authorities.

A personal flotation device that keeps a person's head above water; it must be the correct size, in good condition and worn by all persons on board in adverse conditions.

An emergency in which a person falls into the water; the immediate response is to shout the alarm, throw a float, mark the position and manoeuvre to recover the person.

A document issued by SAMSA certifying that the holder has met the training and examination requirements to act as skipper of a vessel of a stated category and operating area.

A document proving a vessel's national registration and identity, showing its name, official number, tonnage and owner; it must be carried on board.

The legal duties of the person in command to ensure the vessel is seaworthy and properly crewed, that safety equipment is carried, and that the voyage is conducted safely and lawfully.

A vessel's ability to return to an upright position after being heeled by wind or waves, depending on the position of its centre of gravity relative to its centre of buoyancy.

The vertical distance from the waterline to the deck edge or load line; reduced freeboard means less reserve buoyancy and a greater risk of taking water on board.

The loss of stability caused by liquid such as fuel or bilge water moving freely across a tank or bilge when the vessel heels, raising the centre of gravity.

A pump that removes water that has collected in the lowest part of the hull; it may be manual, electric or engine-driven and should be checked before every trip.

A switch that disconnects the battery from the vessel's electrical circuits, used to prevent discharge and reduce fire risk from short circuits when the boat is left unattended.

A valve and skin fitting where a pipe passes through the hull, such as for engine cooling or a drain; it must be accessible and closed if the pipe fails.