At night you do not see a vessel. You see two or three coloured lights, and from their colours, arrangement and arc you must deduce what she is, which way she is heading, and whose job it is to give way.
Everything begins with the arcs. The sectors are not arbitrary — they are cut so that the combination of lights you can see tells you the aspect you are looking at. See both sidelights and you are dead ahead of her. See one sidelight and a masthead light and she is crossing. See only a white sternlight and you are overtaking.
Each sidelight covers 112.5°, from dead ahead to 22.5° abaft its own beam. The sternlight fills the remaining 135°. The masthead light spans 225° — exactly the two sidelights combined. The 22.5°-abaft-the-beam line is also the legal boundary of the overtaking sector in Rule 13.
| VESSEL OR STATUS | LIGHTS AT NIGHT | DAY SHAPE |
|---|---|---|
| Power-driven, under way | Sidelights, sternlight, and one masthead light — two in a vertical line, forward one lower, if 50 m or more. Under 12 m may substitute an all-round white light. | — |
| Sailing vessel, under way | Sidelights and sternlight. Under 20 m may instead use a combined tricolour lantern at the masthead — but never both together. | Cone, point down, if motor-sailing |
| At anchor | All-round white forward; a second aft if 50 m or more | One black ball, forward |
| Aground | Anchor light(s) plus two all-round red in a vertical line | Three black balls in a vertical line |
| Not under command | Two all-round red vertically, plus sidelights and sternlight if making way | Two black balls |
| Restricted in ability to manoeuvre | Red–white–red all-round, vertically | Ball – diamond – ball |
| Constrained by draught | Normal steaming lights plus three all-round red vertically | Black cylinder |
| Fishing, not trawling | Red over white all-round. An extra all-round white toward the gear if it extends more than 150 m. | Two cones, apexes together |
| Trawling | Green over white all-round | Two cones, apexes together |
| Towing, tow 200 m or less | Two masthead lights vertically instead of one, plus a yellow towing light above the sternlight | Black diamond |
| Towing, tow over 200 m | Three masthead lights vertically, plus the yellow towing light | Black diamond on tug and on tow |
| Pilot vessel on duty | White over red all-round at the masthead, plus normal lights | — |
| Dredging or underwater work | Red–white–red, plus two red on the obstructed side and two green on the side you may pass | Ball-diamond-ball, plus two balls / two diamonds on the respective sides |
MEMORY HOOKS THAT SURVIVE AN EXAM
- Red over white, fishing at night. Green over white, trawling in sight.
- Red over red, the captain is dead — not under command.
- Red white red, restricted ahead — restricted in ability to manoeuvre.
- White over red, pilot ahead.
Sound signals
Sound signals are not optional courtesy. In sight of one another, they are how you announce a manoeuvre; in restricted visibility, they are the only thing that says you exist.
IN SIGHT OF ONE ANOTHER — RULE 34
- One short blast — I am altering course to starboard.
- Two short blasts — I am altering course to port.
- Three short blasts — I am operating astern propulsion.
- Five or more short, rapid blasts — the doubt or danger signal: I do not understand your intentions, or what you are doing is not enough to avoid collision. Often supplemented by five rapid light flashes.
- One prolonged blast — approaching a blind bend or an obstruction in a channel. A vessel around the bend must answer with one prolonged blast.
IN RESTRICTED VISIBILITY — RULE 35, AT INTERVALS OF NOT MORE THAN TWO MINUTES
- One prolonged — power-driven vessel making way.
- Two prolonged — power-driven vessel under way but stopped and making no way.
- One prolonged plus two short — not under command, restricted in ability to manoeuvre, constrained by draught, sailing, fishing, or towing. Note that a yacht under sail in fog uses this signal, not one prolonged blast.
- One prolonged plus three short — a manned vessel being towed, sounded immediately after the tug's signal.
- At anchor — rapid ringing of the bell for about five seconds, at intervals of not more than a minute. You may add one short, one prolonged, one short to warn an approaching vessel.
- Aground — the anchor bell signal, with three separate strokes on the bell immediately before and after it.
A short blast is about one second. A prolonged blast is four to six.