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COLREG navigation lights: read a ship at night

At night a ship is just a pattern of lights, and that pattern is a sentence: what she is, which way she is heading, whether she can get out of your way. COLREG gives every vessel type its own signature. Learn the signatures here the way a watchkeeper does: understand the system, study the types, walk around them, then test yourself.

Step 0: the three building blocks (Rule 21)

Almost every signature is built from three arcs, and the arcs are the whole trick: what you see depends on where you stand.

Everything else is all-round lights (360°) in vertical combinations: red-red for not under command, green-white for trawling, and so on. The type cards below take them one by one.

Step 1: learn the 13 signatures

Each card shows the full lights table, day shapes and fog signal, with its own interactive trainer and the classic seafarer's mnemonic.

Navigation lights of a power-driven vessel underway at night, seen from her starboard bow: white forward masthead light, white after masthead light, higher and abaft (50 m and over), green sidelight (starboard) Rule 23 Power-driven vessel underway White masthead light(s), green and red sidelights, white sternlight Navigation lights of a sailing vessel underway at night, seen from her starboard bow: green sidelight (starboard) Rule 25 Sailing vessel underway Sidelights and sternlight only, no masthead light Navigation lights of a sailing vessel with optional red-over-green lights at night, seen from her starboard bow: green sidelight (starboard), red all-round light (upper, at the masthead), green all-round light (lower, at the masthead) Rule 25c Sailing vessel with optional red-over-green lights Sidelights, sternlight, plus red over green at the masthead Navigation lights of a vessel engaged in trawling at night, seen from her starboard bow: green all-round light (upper), white all-round light (lower), green sidelight (when making way) Rule 26b Vessel engaged in trawling Green over white, both all-round Navigation lights of a vessel fishing (other than trawling) at night, seen from her starboard bow: red all-round light (upper), white all-round light (lower), green sidelight (when making way) Rule 26c Vessel fishing (other than trawling) Red over white, both all-round Navigation lights of a vessel not under command (NUC) at night, seen from her starboard bow: red all-round light (upper), red all-round light (lower), green sidelight (when making way) Rule 27a Vessel not under command (NUC) Two red all-round lights in a vertical line Navigation lights of a vessel restricted in ability to manoeuvre (RAM) at night, seen from her starboard bow: red all-round light (upper), white all-round light (middle), red all-round light (lower), white forward masthead light (when making way), white after masthead light (when making way, 50 m and over), green sidelight (when making way) Rule 27b Vessel restricted in ability to manoeuvre (RAM) Red, white, red all-round lights in a vertical line Navigation lights of a dredger with an obstruction (RAM at work) at night, seen from her starboard bow: red all-round light (upper, RAM), white all-round light (middle, RAM), red all-round light (lower, RAM), red all-round light over the obstruction (upper), red all-round light over the obstruction (lower), green all-round light on the clear side (upper), green all-round light on the clear side (lower) Rule 27d Dredger with an obstruction (RAM at work) RAM lights plus red pair over the obstruction and green pair on the clear side Navigation lights of a vessel constrained by her draught at night, seen from her starboard bow: white forward masthead light, white after masthead light (50 m and over), red all-round light (upper), red all-round light (middle), red all-round light (lower), green sidelight (starboard) Rule 28 Vessel constrained by her draught Power-driven lights plus three red all-round lights in a vertical line Navigation lights of a pilot vessel on duty at night, seen from her starboard bow: white all-round light (upper, at the masthead), red all-round light (lower, at the masthead), green sidelight (starboard) Rule 29 Pilot vessel on duty White over red, both all-round, at the masthead Navigation lights of a vessel at anchor at night, seen from her starboard bow: white all-round anchor light, forward (higher) Rule 30 Vessel at anchor White all-round light forward (and a lower one aft) Navigation lights of a vessel aground at night, seen from her starboard bow: white all-round anchor light, forward, red all-round light (upper), red all-round light (lower) Rule 30d Vessel aground Anchor lights plus two red all-round lights in a vertical line Navigation lights of a vessel towing astern at night, seen from her starboard bow: white masthead light (lower of the vertical pair), white masthead light (upper of the pair; three when the tow exceeds 200 m), green sidelight (starboard) Rule 24 Vessel towing astern Two masthead lights in a vertical line plus yellow towing light above the sternlight

Step 2: walk around a ship

The lights trainer puts you on the water: drag around any of the 13 types and watch lights appear and disappear at the Rule 21 sector cut-offs. Dim day into night, roll in fog, play the fog signal. Five minutes of walking around a trawler teaches more than an hour with a table.

Open the trainer

Step 3: take the watch

The lights quiz is the exam version of the night watch: a dark screen, a random bearing, four choices. Ten questions, instant feedback with the mnemonic for every answer.

Start the quiz

All scenes and questions are generated from light positions in metres per COLREG Annex I. Verified by a Master Mariner. Free, and it stays free: safety knowledge never goes behind a paywall here. This is a training aid, not a legal text: in any doubt the Convention wording decides.