COLREG / ARPA / AIS Bridge Rule 19(d)(i) Rule 8 🔒 Course / Simulator plan

RV — Target on Starboard Bow (Rule 19(d)(i))

Fog. Target detected on your starboard bow, forward of the beam. Rule 19(d)(i) forbids alteration to port. She is crossing ahead from starboard to...

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Scenario briefing

Fog. Target detected on your starboard bow, forward of the beam. Rule 19(d)(i) forbids alteration to port. She is crossing ahead from starboard to port: a substantial starboard alteration passes astern of her — or reduce speed.

Applicable COLREG rule(s)

Rule 19(d)(i) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

Rule 8 — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

📸 Bridge simulator scene

Captured directly from the SkipperCheck COLREG bridge simulator at scenario T = 0 — the moment the encounter begins.

SkipperCheck bridge simulator — COLREG Rule 19(d)(i) — Restricted visibility — target on starboard bow — radar PPI with AIS targets — Bridge-simulator scene under COLREG Rule 19(d)(i) — Restricted visibility — target on starboard bow. Captured from the SkipperCheck COLREG / ARPA / AIS bridge simulator.

Key teaching points

Rule 19(d)(i): port alteration is forbidden for any target forward of the beam.
A starboard alteration toward a starboard-bow target must be substantial enough to pass clearly astern, not just nudge.
A speed reduction is often the cleaner answer when the geometry is awkward (Rule 19(e), Rule 6).
Take action in AMPLE time — fog visibility means very short warning if anything goes wrong.

Common mistakes to avoid

Holding course "to let her pass on my starboard side". Rule 19 demands action; you are not the stand-on vessel.
A small starboard turn that closes CPA. The alteration must put you behind her track, not into it.

Why it matters

A target on the starboard bow in fog is the most counter-intuitive Rule 19 case — the rule forbids port alteration, but a starboard alteration draws you TOWARD the target. The correct answer is often a substantial starboard turn to pass well astern, OR a speed reduction.

Exam relevance

The starboard-bow-in-fog case is a probing variation in Yachtmaster Offshore orals — the candidate must reason aloud why starboard turn or speed reduction is correct.

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