RYA Day Skipper Theory flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Latitude scale

The left or right edge of a chart, graduated in degrees and minutes of latitude; one minute equals one nautical mile, so distances are measured on it level with the position.

Chart datum

The reference level from which charted soundings and drying heights are measured, normally Lowest Astronomical Tide; heights of tide are measured upwards from it.

Cocked hat

The small triangle formed when three position lines do not meet at one point; a triangle under about 5 mm on the chart is treated as a fix at its centre.

Running fix

A fix obtained with one object by transferring an earlier position line along the course and distance run, then crossing it with a later position line.

Variation

The angle between true north and magnetic north at a place, shown on the compass rose with its annual change; east variation is added when converting true to magnetic.

Deviation

The angle between magnetic north and compass north caused by the vessel's own magnetic field, recorded on a deviation card and applied when converting magnetic to compass.

Rule of twelfths

A method of estimating tidal height over a six-hour rise or fall: 1/12, 2/12, 3/12, 3/12, 2/12 and 1/12 of the range in successive hours.

Spring tides

The larger tides occurring about one to two days after new and full moon, when the sun and moon pull in line and the tidal range is greatest.

Neap tides

The smaller tides occurring about one to two days after the first and third quarters, when the sun and moon pull at right angles and the range is least.

Secondary port

A port whose tide times and heights are found by applying tabulated time and height differences to the predictions for a named standard port, not from full tables.

Tidal stream set

The direction towards which the horizontal tidal stream flows, expressed in degrees true; it is distinct from the rate, which is the stream's speed in knots.

Under-keel clearance

The depth of water beneath the keel, found as charted depth plus height of tide minus draught, less allowances for squat; keep at least 10% of draught or 0.5 m.

Course to steer

The course through the water that, combined with the tidal stream vector, produces the desired track over the ground; found by a vector triangle.

Estimated position

A position derived from the dead reckoning position by adding estimated leeway and tidal stream; plotted with a square and the time, less reliable than a fix.

Transit

Two charted objects seen in line, giving a position line along the line of the objects; it is used to keep the vessel on track and to check for drift.

Clearing bearing

A bearing to a hazard, drawn on the chart, which keeps the vessel on the safe side of that hazard throughout a leg of the passage.

Passage plan stages

Appraisal, planning, execution and monitoring; the plan covers departure, the passage and arrival, and includes contingencies and abort points.

Sector light

A navigation light showing different colours over different arcs; the white sector is normally the safe one, but the chart or almanac must be checked.

IALA Region A

The buoyage system used in Europe and most of the world, where port-hand marks are red cans and starboard-hand marks are green cones; Region B reverses the colours.

Cardinal marks

Buoys indicating the safe quadrant by cone arrangement: north both up, south both down, east base-to-base, west point-to-point; lights flash 1, 3, 6 or 9.

Rule 5 lookout

Every vessel must at all times maintain a proper lookout by sight and hearing, and by all available means appropriate to the circumstances, to make a full appraisal.

Risk of collision

A steady bearing with decreasing range indicates risk; under Rule 7, if there is any doubt, the risk is deemed to exist.

Overtaking vessel

A vessel coming up on another from more than 22.5 degrees abaft her beam; she must keep clear until finally past and clear, while the overtaken vessel holds course and speed.

Head-on situation

When two power-driven vessels meet on reciprocal or nearly reciprocal courses, both alter course to starboard and pass port-to-port.

Crossing situation

When two power-driven vessels cross, the vessel with the other on her starboard side gives way; the stand-on vessel keeps course and speed but may act if needed.

Restricted visibility rule

Rule 19: proceed at a safe speed, sound the prescribed fog signals and take avoiding action as soon as risk is detected; the steering and sailing rules do not apply.

Fog signal, power making way

A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than two minutes in restricted visibility.

Manoeuvring signals

One short blast means altering to starboard, two short to port, three short operating astern; at least five short rapid blasts means doubt or danger.

MAYDAY

The spoken distress signal used on VHF Ch 16 when a vessel or person is in grave and imminent danger and requires immediate assistance.

MOB recovery

Shout, throw a float, press MOB on the GPS, turn back on a reciprocal course, approach from downwind and recover with the engine in neutral.

Fire triangle

The three elements needed for combustion: fuel, heat and oxygen; removing any one of them extinguishes the fire, and the extinguisher must suit the fuel.

Anchor scope

The length of anchor cable or chain veered, normally about four to five times the depth in settled conditions and more in strong wind or swell.