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COLREG lights trainer

Pick a vessel type and walk around her. Drag across the scene or move the bearing slider and watch the lights appear and disappear exactly where Rule 21 says they should. Dim the day into night, roll in some fog, and play her fog signal. This is how the patterns stop being a table you memorise and start being something you have seen.

Power-driven vessel underway Rule 23

White masthead light(s), green and red sidelights, white sternlight. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged blast at intervals of not more than 2 minutes when making way (Rule 35a); two prolonged when underway but stopped (Rule 35b).

Sailing vessel underway Rule 25

Sidelights and sternlight only, no masthead light. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Sailing vessel with optional red-over-green lights Rule 25c

Sidelights, sternlight, plus red over green at the masthead. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Vessel engaged in trawling Rule 26b

Green over white, both all-round. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Vessel fishing (other than trawling) Rule 26c

Red over white, both all-round. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Vessel not under command (NUC) Rule 27a

Two red all-round lights in a vertical line. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Vessel restricted in ability to manoeuvre (RAM) Rule 27b

Red, white, red all-round lights in a vertical line. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Dredger with an obstruction (RAM at work) Rule 27d

RAM lights plus red pair over the obstruction and green pair on the clear side. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Vessel constrained by her draught Rule 28

Power-driven lights plus three red all-round lights in a vertical line. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts at intervals of not more than 2 minutes (Rule 35c).

Pilot vessel on duty Rule 29

White over red, both all-round, at the masthead. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

As a power-driven vessel; may add four short blasts as the pilot identity signal (Rule 35).

Vessel at anchor Rule 30

White all-round light forward (and a lower one aft). Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

Rapid ringing of the bell for about 5 seconds at intervals of not more than one minute (Rule 35g). From 100 m also a gong aft.

Vessel aground Rule 30d

Anchor lights plus two red all-round lights in a vertical line. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

Three distinct strokes on the bell, rapid ringing for about 5 seconds, then three strokes again (Rule 35h).

Vessel towing astern Rule 24

Two masthead lights in a vertical line plus yellow towing light above the sternlight. Full card: lights table, day shapes, what to watch for →

fog
60°

Drag across the scene to walk around the ship. Tap a light to see its name.

arcs = Rule 21 sectors

One prolonged and two short blasts (Rule 35c). A manned tow answers: one prolonged and three short (Rule 35e).
Test yourself: lights quiz All 13 vessel types

All scenes are generated from light positions in metres per COLREG Annex I, with real sector cut-offs and hull occlusion. Verified by a Master Mariner. Free, and it stays free: safety knowledge never goes behind a paywall here.