COLREG / ARPA / AIS Bridge Rule 25(b) 🔒 Course / Premium

Rule 25(b) - Sailing Tricolour < 20 m

NIGHT. A sailing vessel less than 20 m in length is approaching.

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Scenario briefing

NIGHT. A sailing vessel less than 20 m in length is approaching. She shows, at or near the top of the mast where it can best be seen, a SINGLE lantern combining RED (port arc), GREEN (starboard arc), and WHITE (stern arc) - no other lights are visible. What is this permitted configuration?

Applicable COLREG rule(s)

Rule 25(b) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

📸 Night recognition — 8 aspects

The same vessel rendered every 45° of aspect — bow, starboard bow, beam, quarter, stern, port quarter, beam, bow. Use this strip to learn how the lights present from each approach angle. Click any image to view full size.

Sailing vessel under 20 m with masthead tricolour viewed head-on (bow aspect) — COLREG Rule 25(b) night-recognition diagram — Bow

Sailing vessel under 20 m with masthead tricolour viewed from her starboard bow — COLREG Rule 25(b) night-recognition diagram — STBD bow

Sailing vessel under 20 m with masthead tricolour viewed from her starboard beam — COLREG Rule 25(b) night-recognition diagram — STBD beam

Sailing vessel under 20 m with masthead tricolour viewed from her starboard quarter — COLREG Rule 25(b) night-recognition diagram — STBD qtr

Sailing vessel under 20 m with masthead tricolour viewed dead astern (stern aspect) — COLREG Rule 25(b) night-recognition diagram — Stern

Sailing vessel under 20 m with masthead tricolour viewed from her port quarter — COLREG Rule 25(b) night-recognition diagram — Port qtr

Sailing vessel under 20 m with masthead tricolour viewed from her port beam — COLREG Rule 25(b) night-recognition diagram — Port beam

Sailing vessel under 20 m with masthead tricolour viewed from her port bow — COLREG Rule 25(b) night-recognition diagram — Port bow

Key teaching points

Rule 25(b): a sailing vessel less than 20 m may carry, instead of the separate sidelights/sternlight, a TRICOLOR at the top of the mast.
Tricolor sectors: red (port), green (starboard), white (sternlight), totalling 360°.
A vessel showing tricolor MAY NOT also display Rule 25(c) red-over-green — the two are mutually exclusive (Rule 25(b)).
The tricolor is masthead-mounted, NOT a masthead light — there is no white forward-facing arc.

Common mistakes to avoid

Reading a tricolor at distance as a masthead light + sidelights, mis-classifying the vessel as a small power-driven craft.
Lighting both tricolor AND Rule 25(c) red-over-green — explicitly forbidden by the rules.

Why it matters

Rule 25(b) gives sailing vessels under 20 m a clean alternative — a single tricolor lantern at the masthead. Misreading it as some other category, or missing it entirely from astern, leaves a sailing yacht effectively invisible on a busy night.

Exam relevance

Tricolor recognition is a frequent oral probe in RYA Yachtmaster Coastal/Offshore and Coastal Skipper exams.

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