COLREG / ARPA / AIS Bridge Rule 27(a) Rule 27(b) 🔒 Course / Premium

Rule 27 — NUC / RAM Lights

NIGHT. You observe a vessel showing at her masthead THREE all-round lights in a vertical line: RED WHITE RED.

🔒

This scenario is part of the full library. Unlock all 54 COLREG scenarios with the Skipper Refresher Course (€99.99, lifetime + certificate) or a Premium subscription (from €19.99/mo).

Buy Skipper Refresher — €99.99 Or get Premium — from €19.99/mo

Scenario briefing

NIGHT. You observe a vessel showing at her masthead THREE all-round lights in a vertical line: RED WHITE RED. She is making way through the water and also shows sidelights and a sternlight. What is she?

Applicable COLREG rule(s)

Rule 27(a) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

Rule 27(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.

Vessel not under command / restricted in ability to manoeuvre viewed head-on (bow aspect) — COLREG Rule 27 night-recognition diagram — Bow

Vessel not under command / restricted in ability to manoeuvre viewed from her starboard bow — COLREG Rule 27 night-recognition diagram — STBD bow

Vessel not under command / restricted in ability to manoeuvre viewed from her starboard beam — COLREG Rule 27 night-recognition diagram — STBD beam

Vessel not under command / restricted in ability to manoeuvre viewed from her starboard quarter — COLREG Rule 27 night-recognition diagram — STBD qtr

Vessel not under command / restricted in ability to manoeuvre viewed dead astern (stern aspect) — COLREG Rule 27 night-recognition diagram — Stern

Vessel not under command / restricted in ability to manoeuvre viewed from her port quarter — COLREG Rule 27 night-recognition diagram — Port qtr

Vessel not under command / restricted in ability to manoeuvre viewed from her port beam — COLREG Rule 27 night-recognition diagram — Port beam

Vessel not under command / restricted in ability to manoeuvre viewed from her port bow — COLREG Rule 27 night-recognition diagram — Port bow

Key teaching points

Rule 27(a): NUC vessel shows TWO all-round RED lights vertically, where best seen.
Rule 27(b): RAM vessel shows THREE all-round lights vertically — RED OVER WHITE OVER RED.
NUC and RAM both add normal lights for their size when making way (Rule 27(a)(ii), 27(b)(iii)).
Day equivalent: NUC = two balls; RAM = ball-diamond-ball.

Common mistakes to avoid

Confusing red-red (NUC) with red-over-green (sailing vessel optional under Rule 25(c)) — different patterns, different priorities.
Confusing RAM (red-white-red) with fishing (red-over-white) — the third red below is the give-away.

Why it matters

NUC and RAM both signal serious limitations on the vessel's manoeuvring ability — and Rule 18 puts them at the top of the priority list. The visual difference is the centre light: white in RAM (red-WHITE-red), absent in NUC (red-red). One letter, one light, very different vessel.

Exam relevance

Rule 27 NUC/RAM lights are a centrepiece oral question in STCW OOW and a regular probe in Yachtmaster Offshore exams.

Related scenarios

About SkipperCheck simulators

SkipperCheck offers two browser-based maritime training simulators:

ARPA · AIS · COLREG Bridge Simulator — 54 scenarios covering Rules 2, 5–10, 12–19, 23–30, 34 and 35.
VHF SRC Radio Simulator — 15 scenarios: voice Mayday, DSC distress, Mayday Relay, Pan-Pan, Sécurité, routine.

Both run in any modern browser, on desktop or mobile. No install, no plugins.