COLREGs theory: everything the ICC and Day Skipper exam asks

Rule 5: keep a proper lookout at all times, by sight and hearing and by all available means, radar included. A phone, an autopilot and a chat in the cockpit are not a lookout.

Rule 6: safe speed is the speed at which you can stop within the distance that matters in those conditions. It is set by visibility, traffic density, manoeuvrability, background lights and shore, sea and wind state, and draught against the depth.

Rule 7: the main sign is a steady bearing with a decreasing range. If the direction to the other vessel holds and she is getting bigger, you are heading for the same spot.

A changing bearing does not clear you: with a very large vessel, with a tow and at close range risk can still exist. Scanty information counts as risk too, so if in doubt, risk exists.

Rule 8: any action is taken early, is large enough to be obvious, and is readily apparent to the other vessel visually and by radar. A string of small alterations is forbidden: nobody can read it.

A course change usually reads better than a speed change. Pass at a safe distance and keep checking the result until the other vessel is finally past and clear. If need be, slacken speed or take all way off: stopping is a manoeuvre too.

Every vessel keeps out of the way of everyone above her. A yacht under engine, a motorboat and a jet ski are a power-driven vessel, that is the bottom step: they give way to almost everything.

A seaplane and a wing-in-ground craft stay well clear of everybody and hamper nobody.

One caveat about the third step: a vessel constrained by her draught sits in the ladder by sense, but rule 18 (d) asks the others not to give way to her, only to avoid impeding her safe passage. Examiners love that difference.

Not size, not flag, not the price of the boat and not local habit. Sail loses the high step the second the engine goes on: with the engine running a yacht is a power-driven vessel, and by day she must show a cone point down.

A vessel engaged in fishing means gear that restricts manoeuvrability. A rod over the rail does not make a yacht a fishing vessel.

The night sign: you see both sidelights of the other vessel and her masthead lights in line. By day: she is ahead or nearly ahead of you.

Both vessels alter course to starboard and pass port to port. The duty is mutual, so waiting for the other one is not an option. If in doubt whether it is a head-on situation, act as if it is.

The vessel that has the other on her starboard side gives way. At night the colour decides: you see her red sidelight, so you give way.

The rule says to avoid crossing ahead of the other vessel if the circumstances admit, so the give-way vessel alters to starboard and passes astern. Rule 15 does not itself order a turn to starboard: that follows from rule 8 (make it obvious) and from the words of rule 15 about not crossing ahead. Rule 17 (c) is about something else, it binds the stand-on vessel when she acts alone and forbids her to alter to port for a vessel on her own port side.

Overtaking means coming up from more than 22.5 degrees abaft her beam. The night check is simple: you see only her sternlight and no sidelight at all.

The overtaking vessel keeps out of the way until she is finally past and clear. Any later change of bearing does not turn her into a crossing vessel.

The give-way vessel acts early and substantially (16). The stand-on vessel keeps her course and speed (17) so that the two manoeuvres do not cancel each other.

As soon as it is clear that the give-way vessel is not acting, the stand-on vessel may manoeuvre alone, and when collision cannot be avoided by the give-way vessel alone she shall. Acting alone, a power-driven vessel shall not, if the circumstances of the case admit, alter course to port for a vessel on her own port side (17 (c)).

• Masthead light: white, 225 degrees, ahead and 22.5 degrees abaft the beam on each side.
• Sidelights: green to starboard, red to port, 112.5 degrees each.
• Sternlight: white, 135 degrees, shining astern.
• All-round light: 360 degrees, seen from everywhere.
• Flashing light: all-round, at least 120 flashes per minute.

A forward masthead light, a second masthead light abaft and higher, sidelights and a sternlight. A vessel under 50 metres may omit the second masthead light, so two whites in a vertical line suggest a large ship.

A vessel under 12 metres may show an all-round white plus sidelights instead of masthead and sternlight. Under 7 metres and under 7 knots one all-round white is enough, plus sidelights if practicable.

Always in the same order: colours first, then the whites, then how they sit above one another.

• Green and red together: she is heading towards you.
• Green only: her starboard side, she crosses from left to right, she gives way.
• Red only: her port side, she crosses from right to left, you give way.
• White only: you are most likely in her stern sector, so you are overtaking.

An all-round flashing yellow light in addition to her ordinary lights means an air-cushion vessel in non-displacement mode, a yellow light above the sternlight of a tug is the towing light, and a high intensity all-round flashing red light is a wing-in-ground craft taking off, landing or in flight near the surface.

Shapes read like the lights: two identical balls mean a total loss of control, a ball with a diamond between them means restricted manoeuvring, and a cone is always about an engine under sail.

In fog there is no stand-on vessel: the steering rules about who gives way do not apply, and the duties are mutual.

Keep a safe speed with the engine ready for immediate manoeuvre. If you detect a vessel by radar alone, decide whether risk exists and take avoiding action in good time, avoiding two moves: an alteration to port for a vessel forward of the beam, other than for a vessel being overtaken, and an alteration towards a vessel abeam or abaft the beam.

If you hear a fog signal forward of the beam and cannot be sure the situation is clear, reduce to bare steerage way and if necessary take all way off.

Keep as near to the outer limit of the channel on your starboard side as is safe and practicable.

A vessel under 20 metres and a sailing vessel shall not impede a vessel that can navigate only within the channel. Do not cross the channel if that impedes such a vessel. Every vessel shall avoid anchoring in a narrow channel if the circumstances of the case admit.

Proceed in the lane in the general direction of traffic, join and leave at the ends, and if joining from the side do so at as small an angle as practicable.

So far as practicable avoid crossing traffic lanes at all; if you must cross, do it on a heading as nearly as practicable at right angles to the general direction of traffic flow. A vessel under 20 metres and a sailing vessel shall not impede the safe passage of a power-driven vessel following a lane (10 (j)); a vessel engaged in fishing shall not impede any vessel following a lane (10 (i)).

Sides are counted along the conventional direction of buoyage: usually from seaward into a harbour or a river, or clockwise around a landmass. The chart shows it with an arrow.

In region A (all of Europe) the port side is a red can, the starboard side a green cone. In region B (Americas, Japan, Korea, the Philippines) the colours swap while the shapes stay. A preferred channel mark is the same can or cone with a band of the other colour. Pass it as an ordinary lateral mark of its main colour and you stay in the preferred, that is the main, channel; the secondary channel lies on the other side of the buoy.

A cardinal mark is named after the side you pass it: pass a north mark to the north, a west mark to the west. The danger lies on the opposite side.

The colours copy the cones: both points up means the black band on top (north), both down means black at the bottom (south), base to base means black top and bottom (east), point to point means black in the middle (west). The light is always white and quick.

At night you tell the mark by the number of flashes, laid out like the numbers on a clock: east is 3, south 6, west 9, north 12, that is, no break at all. The south mark adds a long flash after the six, which is what separates it from the west mark when you lose count.

• Isolated danger: black with a red band, two black balls on top. It stands right over a small shoal or rock with deep water all around. Pass either side, but not close.
• Safe water (mid-channel): red and white vertical stripes, a single red ball on top. Deep water under it: the axis of a channel, a landfall, the middle of a passage. You may pass either side of it; in practice, keeping to the starboard side of the channel, you leave it to port.
• Special mark: yellow, a yellow saltire cross on top. It marks a special area or feature: cables, pipelines, firing ranges, fish farms, swimming areas. By itself it neither forbids passage nor indicates a navigational danger; the rules of the area are in the pilot book and local regulations.
• Emergency wreck (new danger): blue and yellow vertical stripes, an upright yellow cross, a light alternating blue and yellow. A fresh danger not yet on the chart, most often a wreck.

Fl(2) R 10s 12m 6M reads: two flashes in a group, the light is red, the whole cycle repeats every 10 seconds, the light stands 12 metres above mean high water springs, and 6M is its nominal range, the distance it carries in a standard visibility of 10 miles; what you actually see also depends on your height of eye.

A lighthouse is a major light shown from a permanent structure, listed with its full character in the Admiralty List of Lights. Lights are lit at sunset and put out at sunrise. Neighbouring lights are given different characters, so that two of them cannot be taken for each other.

Where there is a danger the lighthouse shows different colours in different directions: a red sector is danger, a green sector is the other side of the channel, white is the safe approach. The colour changes as you cross the sector line, and that change is the signal to alter course.

Lit beacons are the same idea in a smaller, lower structure. Unlit beacons and daymarks serve for fixing your position by day, and a fog signal may sit beside them.

Latitude runs from the equator to 90 degrees north or south, longitude from Greenwich to 180 degrees east or west. Written as 42°24.4' N and 018°23.2' E: degrees, minutes and tenths of a minute.

One minute of latitude is one nautical mile: 1 mile is 1852 metres, and 1 knot is one mile per hour. Take distance only from the side scale of the chart and at your own latitude, because on a Mercator chart the latitude scale stretches the further you go from the equator, so a minute at your latitude is longer than a minute at the equator.

Heading is the angle from north to the fore and aft line of the boat, measured clockwise: that is where the bow points, while the course to steer is the heading you order and the track is the line drawn on the chart. A bearing is the angle from north to an object, and the reciprocal bearing differs by 180 degrees. A relative bearing is measured from the bow, to port or starboard, from 0 to 180.

The course over ground is where you actually go: your heading plus leeway and the set and drift of the tidal stream. The chart carries the track, the helm keeps the heading.

Variation is the angle between the true and the magnetic meridian. It differs by area and changes year by year: take it from the chart and correct it to the year of the passage. Deviation is the pull of the boat's own iron on the card, taken from the deviation table.

Compass error is the sum of both: error = variation + deviation. Converting: true = compass + error, and back compass = true - error. Only true directions are plotted on and taken from the chart.

Three norths give three sets of the same numbers. Two corrections sit between them: variation (Var) (true against magnetic) and deviation (Dev) (magnetic against compass).

The formulas examiners want word for word: error = variation + deviation, true = compass + error, compass = true - error. A reciprocal bearing differs from the direct one by 180 degrees, and a relative bearing is counted from the bow, not from north.

At new and full moon the Sun, the Earth and the Moon line up, the forces add and the tides are the biggest: spring tides. At the first and third quarter the Moon stands at a right angle, the forces subtract and the tides are the smallest: neap tides. About 7 days lie between springs and neaps.

The more enclosed the sea, the smaller the tide: tens of centimetres in the Mediterranean, metres in the ocean.

The water does not rise evenly, it follows a sine curve. Between high and low water lie about six hours, and the range is split as 1/12 in the first hour, then 2/12, 3/12, 3/12, 2/12, 1/12. Half the water arrives in the middle two hours.

The depth at that moment is the charted depth (measured from chart datum) plus the height of tide. Under-keel clearance is another thing: from that depth you subtract your draught and a safety margin.

The tidal wave creates a stream that turns four times a day. The flood sets towards the land, the ebb back out to sea. At high and low water the rate is near zero, the maximum falls halfway between them.

At anchor that means the boat swings through 180 degrees four times a day, once for every turn of the stream: choose a berth with room all around and depth to spare at low water.

A weather chart carries isobars (lines of equal pressure), fronts and pressure areas. The tighter the isobars, the stronger the wind. H is high pressure, usually clear; L is low, cloud and rain. The wind runs from high to low.

The main sign of change is the barometric tendency, the change of pressure over three hours. A fast fall means wind arriving fast.

A depression is an area of low pressure (L). In the northern hemisphere the wind in it turns anticlockwise and spirals in towards the centre. Weather: cloud, rain, fresh wind and a shift of wind as the fronts go through.

An anticyclone is an area of high pressure (H). In the northern hemisphere the wind turns clockwise and spreads out from the centre. Weather: clear sky, light wind, heat in summer, fog in winter.

In the southern hemisphere it is all mirrored: clockwise in a low, anticlockwise in a high. Europe, the Mediterranean and the Black Sea are northern hemisphere, so a depression there turns anticlockwise.

A trough is a tongue of low pressure reaching out of a depression, a ridge the same tongue of high pressure out of an anticyclone. On a trough the wind shifts in one jump.

When the cold front catches the warm one you get an occluded front: mixed weather that changes fast.

Three storeys. High cirrus of ice crystals: the first hint of a warm front a day ahead. Middle alto clouds at 2 to 6 km. Low stratus and cumulus below 2 km.

The one to watch is cumulonimbus: a vertical tower with an anvil. Under it sit squall, thunder and sometimes hail. See that tower on your course and reef early.

The sea breeze: by day the land warms faster than the water, the warm air rises and air comes in from the sea to fill the gap. It reaches about 10 miles offshore, runs roughly from 10:00 to 17:00 and blows up to 15 knots. At night it reverses and blows off the land onto the sea.

A katabatic wind is cold air sliding down high mountains to the sea at night. It reaches about 2 miles offshore. Gusts of 40 to 60 knots are normal and in some areas they reach 100. That is why you do not anchor tight under a high cliff.

True wind (TWS for speed, TWD for direction) is the wind over the water. Apparent wind (AWS, AWA) is what the boat feels under way: the true wind plus the headwind of her own movement.

Alongside they are the same. Under way the apparent wind always draws forward, and on a close course it feels stronger than it is. That is why a sailing autopilot steers to the apparent wind while every forecast speaks of the true one.

Transmitter power is 1 or 25 watts, and the range depends on aerial height, usually tens of miles. Three levels of message: MAYDAY (life in danger), PAN-PAN (urgency without danger to life), SECURITE (safety: weather, a warning).

MAYDAY three times, then THIS IS with the vessel name three times, her call sign and MMSI, then MAYDAY, the vessel name and MMSI once more, and after that, in order: the position (coordinates, or bearing and distance from a known object), what happened, what help you need, how many people are aboard, any extra information, and the word Over.

A false alert must be cancelled, and it is cancelled like this: Mayday, All stations three times, this is (vessel name, call sign, MMSI number), cancel my distress alert of (time in UTC). If you hear a MAYDAY that the shore station clearly does not, you pass it on as a MAYDAY RELAY.

A vessel name, a call sign and a position go over the air letter by letter: on the radio you cannot tell B from D by ear. The alphabet is international and marina staff use the same one.

Pick the spot on four things: shelter from tomorrow's forecast, even depth without sudden steps, the bottom (sand is good, rock and coral are bad) and no cables or pipelines on the chart.

Veer at least five times the depth of chain. Come up into the wind, take the way off, drop the anchor and pay the chain out going astern so it lies along the bottom instead of piling under the boat. Then go astern up to 2000 revs: if the shore transits do not move, the anchor is holding. Finish with the anchor light on and an anchor alarm set.

Weighing: motor up to the anchor so the chain comes vertical, then heave. If the windlass changes its note, stop: the chain is under the boat or the anchor is snagged.

The drill is learnt word for word: shout man overboard, throw the horseshoe with its buoy, appoint a spotter who never takes their eyes off and keeps pointing, press MOB on the plotter, come back and approach from downwind at slow speed. On the radio this is a MAYDAY with the words man overboard.

The bowline: a loop in the end of a line that will not tighten. It holds under load and unties once the load is off. You throw it to someone in the water, bend it onto a sheet, drop the loop over a cleat.

The fender hitch, a round turn and two half hitches on the guardrail: it keeps the fender at the height you set, adjusts with one hand and does not creep down as the fender rubs the topsides.

Towards you: take up (tension it hard, on a winch if you have to), sweat it in (a little tighter than it is now), take up the slack (pull the belly out of it without a winch), make fast (secure it on the cleat or in the clutch with the tension on).

Away from you: ease (let it go slack to zero tension), ease a touch (let off a little), check or surge (let it run but hold the load with a turn on the cleat), let go (cast it off completely).

• New Reels Catch Fish So Purchase Some: the give-way ladder from the top down.
• Red means stop, green means go: her red sidelight means you give way.
• Red over red, the captain is dead: not under command.
• White over red, pilot ahead.
• Red over white, fishing at night, gear in the water.
• Red over green, sailing machine.
• Balls mean stopped: one at anchor, three aground.
• Cone down means engine on.
• One short, one starboard, two short to port, three short astern, five short mean I do not understand.
• In fog never turn to port.
• If in doubt, you are overtaking, so keep clear.