COLREG / ARPA / AIS Bridge Rule 19(d)(ii) 🔒 Course / Premium

RV — Target Abeam Starboard (Rule 19(d)(ii))

A target is detected abeam on your starboard side (relative bearing ~090).

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Scenario briefing

A target is detected abeam on your starboard side (relative bearing ~090°). Rule 19(d)(ii): AVOID alteration of course TOWARD a vessel abeam or abaft the beam. A starboard alteration is therefore prohibited here. Consider a port alteration or speed change.

Applicable COLREG rule(s)

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

Key teaching points

Rule 19(d)(ii): avoid alteration of course TOWARD a vessel abeam or abaft the beam.
For a target abeam starboard: port alteration is acceptable, starboard is forbidden.
Speed reduction is often the safest action when targets are abeam — it opens CPA without geometric ambiguity.
Re-check CPA after the action — abeam targets can close quickly if their course curves toward you.

Common mistakes to avoid

Treating Rule 19(d)(i) as the only sub-rule — there are TWO prohibitions, and the abeam case is governed by (d)(ii).
Turning toward a CPA-closing target on the basis that "fog visibility is OK now". Rule 19 still applies.

Why it matters

A target abeam in fog flips the Rule 19 logic — Rule 19(d)(ii) now prohibits alteration TOWARD the target. With a target abeam starboard, you cannot turn to starboard. The available actions are port turn (allowed for abeam/abaft targets) or speed change.

Exam relevance

Rule 19(d)(ii) is the harder of the two fog prohibitions and a deliberate probe in STCW OOW and Yachtmaster Offshore orals.

Related scenarios

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