COLREG / ARPA / AIS Bridge
Rule 23(a)
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Rule 23 — Power-Driven Vessel Underway Lights
NIGHT. You observe the following lights approaching from ahead: two MASTHEAD lights in a vertical line (fore lower, after higher); RED sidelight on the...
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Scenario briefing
NIGHT. You observe the following lights approaching from ahead: two MASTHEAD lights in a vertical line (fore lower, after higher); RED sidelight on the left, GREEN sidelight on the right; white sternlight not visible (you are ahead of her beam); vessel appears > 50 m in length. What type of vessel is this?
Applicable COLREG rule(s)
Rule 23(a) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.
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.