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

Rule 25 — Sailing Vessel Underway Lights

NIGHT. You see an approaching vessel showing: red & green sidelights; white sternlight (she is heading generally toward you and slightly past); NO...

🔒

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 see an approaching vessel showing: red & green sidelights; white sternlight (she is heading generally toward you and slightly past); NO masthead light at all. Optionally: two all-round lights at the top of the mast RED OVER GREEN. What type of vessel is this?

Applicable COLREG rule(s)

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

Rule 25(c) — 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 way viewed head-on (bow aspect) — COLREG Rule 25 night-recognition diagram — Bow

Sailing vessel under way viewed from her starboard bow — COLREG Rule 25 night-recognition diagram — STBD bow

Sailing vessel under way viewed from her starboard beam — COLREG Rule 25 night-recognition diagram — STBD beam

Sailing vessel under way viewed from her starboard quarter — COLREG Rule 25 night-recognition diagram — STBD qtr

Sailing vessel under way viewed dead astern (stern aspect) — COLREG Rule 25 night-recognition diagram — Stern

Sailing vessel under way viewed from her port quarter — COLREG Rule 25 night-recognition diagram — Port qtr

Sailing vessel under way viewed from her port beam — COLREG Rule 25 night-recognition diagram — Port beam

Sailing vessel under way viewed from her port bow — COLREG Rule 25 night-recognition diagram — Port bow

Key teaching points

Rule 25(a): sailing vessel underway shows sidelights and a sternlight, with NO masthead light.
Rule 25(c): optionally, two all-round lights at or near the top of the mast — RED OVER GREEN — to identify herself.
A sailing vessel under sail AND power is a power-driven vessel for Rule 23 — the sailing identifier disappears.
Day equivalent: Rule 25(e) — a conical shape, apex downward, where best seen, when sailing AND propelled by machinery.

Common mistakes to avoid

Searching for a masthead light and concluding the contact is a small power-driven vessel under Rule 23(d). Absence of masthead = sailing.
Confusing the red-over-green of Rule 25(c) with the red-over-red NUC pattern.

Why it matters

A sailing vessel under way shows no masthead light — that absence is the first identifier. Add to that the optional red-over-green masthead arrangement and the recognition is unambiguous. Watchkeepers who scan for masthead lights and find none must consider sailing vessel before any other category.

Exam relevance

Rule 25 lights are paired with Rule 18(a)(iv) priority in nearly every yachting oral; STCW OOW candidates must also know the optional Rule 25(c) lights.

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.