COLREG / ARPA / AIS Bridge Rule 18(a)(iv) Rule 16 ✓ Free demo

Power-Driven Gives Way to Sailing Vessel (Rule 18(a)(iv))

AIS identifies the target as a sailing vessel (badge "S"). You are a power-driven vessel Rule 18(a)(iv): a power-driven vessel under way shall keep out...

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Scenario briefing

AIS identifies the target as a sailing vessel (badge "S"). You are a power-driven vessel Rule 18(a)(iv): a power-driven vessel under way shall keep out of the way of a sailing vessel. Take early and substantial action, CPA 1 NM in open water.

Applicable COLREG rule(s)

Rule 18(a)(iv) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.

Rule 16 — 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 18(a)(iv) — Power-driven gives way to sailing vessel — radar PPI with AIS targets — Bridge-simulator scene under COLREG Rule 18(a)(iv) — Power-driven gives way to sailing vessel. Captured from the SkipperCheck COLREG / ARPA / AIS bridge simulator.

Key teaching points

Rule 18(a)(iv): a power-driven vessel under way shall keep out of the way of a sailing vessel.
Exceptions: Rule 9(b) (sailing vessel shall not impede a vessel constrained to a narrow channel) and Rule 10(j) (TSS).
A sailing vessel under both sail AND power is a power-driven vessel under Rule 25(e) — the priority disappears.
Take early, substantial action — a bold starboard turn to pass astern is the textbook response.

Common mistakes to avoid

Holding course toward a sailing yacht "because she should keep clear of me — I'm bigger". Bigger doesn't change the rule.
Crossing ahead of a sailing vessel at close quarters. Rule 18 + Rule 16 demand early action that passes astern.

Why it matters

Rule 18(a)(iv) is one of the most-forgotten rules among recreational motorboaters — a sailing vessel under sail outranks a power-driven vessel, period (subject to the narrow channel and TSS exceptions). The rule's practical importance grows with mixed-fleet waters like the Solent, the Adriatic and Long Island Sound.

Exam relevance

Rule 18(a)(iv) is examined in nearly every recreational and commercial COLREG oral — examiners often combine it with a Rule 25 light-recognition question at night.

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