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.

🔒

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 €29.99/mo).

Buy Skipper Refresher — €99.99 Or get Premium — from €29.99/mo

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

Why it matters

COLREG knowledge is the foundation of safe ship handling. Most maritime collisions happen because watchkeepers either misidentified the situation, applied the wrong rule, or acted too late. This scenario lets you train pattern recognition + correct response under time pressure — the exact skill the rules are designed to support. RYA, Yachtmaster, STCW and most national exams expect you to apply COLREGs reflexively, not just recite them.

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.