IALACOLREG

Lights & Shapes

COLREG Part C (Rules 20–31) defines the lights shown at night and the day shapes hoisted by different vessel types — power-driven vessels, sailing vessels, vessels not under command, restricted in ability to manoeuvre, fishing, pilot, anchored and aground.

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Lights & Shapes — Cheat Sheet

Every variant from Rules 23–30 in one place. Each row shows the lights as seen from port, starboard, ahead, and astern, plus the day shape — designed for fast revision before an exam.

Open cheat sheet

Reading vessel lights — the framework that actually works

Identifying a vessel at night is a three-step process: count the white lights, find the coloured sidelights, then read the topmarks. A power-driven vessel underway shows one or two masthead whites (depending on length), a sternlight, and a red/green sidelight pair. Add a red-over-red and she is not under command. Add red-white-red and she is restricted in ability to manoeuvre. Swap the white masthead for a green-over-white and she is trawling.

Day shapes are the daytime equivalent. A black ball means anchored or, in pairs/triples, restricted manoeuvring. A black cone point-down is a sailing vessel under engine. A black cylinder is constrained by draught. The IMO chose these shapes to be unambiguous at distance — once you know the seven canonical shapes (ball, cone, diamond, cylinder, two-cones-apex-together, two-cones-base-together, flag A) you can read every Part C signal.

Rules 23–31 cover specific vessel categories: power-driven (23), towing and pushing (24), sailing and rowing (25), fishing (26), NUC and RAM (27), constrained by draught (28), pilot (29), anchored and aground (30), seaplanes and WIG (31). Below you'll find every rule — the 3D viewer shows the lights in their geometric positions, the cheat sheet poster shows every variant in one scrollable page, and the visual quiz tests whether you can recognise them.

Fastest routes through the lights syllabus

Frequently asked questions

What are the basic navigation lights every power-driven vessel shows?
A masthead white light forward (and a second masthead aft if the vessel is 50 m or longer), a green sidelight on the starboard bow, a red sidelight on the port bow and a white sternlight aft. The sidelights cover 112.5° each from dead-ahead to 22.5° abaft the beam, the sternlight covers the remaining 135° astern, and the masthead lights cover the same 225° forward arc as the two sidelights combined.
What does red over white mean?
Red over white, all-round, means a pilot vessel on duty (Rule 29). She will also show her ordinary running lights. Two reds (red over red) mean "not under command". Red-white-red means "restricted in ability to manoeuvre". Three reds vertically mean "constrained by draught". Memorise the mnemonics — they come up in every exam.
When does a sailing vessel show a black cone point-down?
A sailing vessel that is also being propelled by machinery must, by day, exhibit forward where it can best be seen a conical shape, apex downwards (Rule 25(e)). At night she shows the normal power-driven lights. The cone signals "I am no longer a sailing vessel for collision-avoidance purposes" — she has no privilege under Rule 18.
What does a single black ball mean during the day?
One black ball forward means "vessel at anchor" (Rule 30(a)). Two black balls in a vertical line mean "vessel aground". Three black balls in a vertical line indicate a vessel constrained by draught (Rule 28). Day shapes are read top-down and at distance — visibility is more important than detail.
Do I need to show lights during the day in restricted visibility?
Yes. Rule 20(b): the lights prescribed by these Rules shall be exhibited from sunset to sunrise, and may also be exhibited from sunrise to sunset in restricted visibility and in all other circumstances when it is deemed necessary. In dense fog, switching on the lights is good seamanship even at noon.