COLREG / ARPA / AIS Bridge Rule 23(d) 🔒 Course / Premium

Rule 23(d) — PDV < 7 m AND < 7 kn

NIGHT. A very small power-driven vessel is observed. Her length is less than 7 m and her maximum speed does not exceed 7 kn.

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Scenario briefing

NIGHT. A very small power-driven vessel is observed. Her length is less than 7 m and her maximum speed does not exceed 7 kn. She exhibits ONE all-round WHITE light and, if practicable, sidelights. No masthead light, no separate sternlight. What allowance permits this reduced lighting?

Applicable COLREG rule(s)

Rule 23(d) — 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.

Power-driven vessel under 7 m and under 7 kn viewed head-on (bow aspect) — COLREG Rule 23(d) night-recognition diagram — Bow

Power-driven vessel under 7 m and under 7 kn viewed from her starboard bow — COLREG Rule 23(d) night-recognition diagram — STBD bow

Power-driven vessel under 7 m and under 7 kn viewed from her starboard beam — COLREG Rule 23(d) night-recognition diagram — STBD beam

Power-driven vessel under 7 m and under 7 kn viewed from her starboard quarter — COLREG Rule 23(d) night-recognition diagram — STBD qtr

Power-driven vessel under 7 m and under 7 kn viewed dead astern (stern aspect) — COLREG Rule 23(d) night-recognition diagram — Stern

Power-driven vessel under 7 m and under 7 kn viewed from her port quarter — COLREG Rule 23(d) night-recognition diagram — Port qtr

Power-driven vessel under 7 m and under 7 kn viewed from her port beam — COLREG Rule 23(d) night-recognition diagram — Port beam

Power-driven vessel under 7 m and under 7 kn viewed from her port bow — COLREG Rule 23(d) night-recognition diagram — Port bow

Key teaching points

Rule 23(d)(i): a power-driven vessel less than 12 m in length may exhibit an all-round white light and sidelights, instead of masthead + sternlight.
Rule 23(d)(ii): vessels under 7 m and max speed ≤7 kt may exhibit an all-round white light alone (sidelights if practicable).
These options are PERMITTED, not mandatory — small craft may still show the full standard pattern.
A single white light with sidelights and no sternlight = small PDV under 12 m.

Common mistakes to avoid

Treating a single all-round white light as a vessel at anchor — Rule 30 vs Rule 23(d)(i) ambiguity is the most-tested visual confusion.
Assuming all small commercial craft show the simplified pattern. Many show the full Rule 23(a) lights anyway.

Why it matters

A power-driven vessel under 12 metres has a simplified lights option — Rule 23(d)(i) — that watchkeepers often forget exists. Recognising the simplified pattern prevents misclassifying small commercial craft and yachts.

Exam relevance

Rule 23(d) is a fine-detail probe in Yachtmaster Coastal/Offshore orals; STCW OOW candidates also need to recognise it.

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