COLREG / ARPA / AIS Bridge Rule 12(a) 🔒 Course / Premium

Rule 12 — Sailing vs Sailing

Clear visibility. You are under SAIL with the wind on your PORT side (port tack).

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Scenario briefing

Clear visibility. You are under SAIL with the wind on your PORT side (port tack). A SAILING vessel ahead has the wind on her STARBOARD side (starboard tack). Rule 12(a)(i): when vessels have the wind on different sides, the vessel with the wind on the PORT side shall keep out of the way of the other. You are therefore GIVE-WAY. Make a substantial alteration ( 20°) and achieve CPA 0.3 NM.

Applicable COLREG rule(s)

Rule 12(a) — 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 12 — Sailing vessel meeting sailing vessel — radar PPI with AIS targets — Bridge-simulator scene under COLREG Rule 12 — Sailing vessel meeting sailing vessel. Captured from the SkipperCheck COLREG / ARPA / AIS bridge simulator.

Key teaching points

Rule 12(a)(i): when each has the wind on a different side, the vessel with wind on her PORT side keeps out of the way.
Rule 12(a)(ii): when both have wind on the same side, the WINDWARD vessel keeps out of the way of the leeward vessel.
Rule 12(a)(iii): if a port-tack vessel cannot determine the tack of a windward vessel, she keeps out of the way.
"Windward side" is the side OPPOSITE to which the mainsail is carried.

Common mistakes to avoid

Applying racing right-of-way rules (RRS) instead of COLREG Rule 12. The two differ, and only COLREG governs the open sea.
Confusing the "same side" sub-rule — windward must give way, NOT leeward.

Why it matters

Sailing-vs-sailing right-of-way is the rule yacht racers think they know but routinely break in cruising. Rule 12 has three different priorities and they apply in a specific order — get the order wrong and the wrong vessel gives way.

Exam relevance

Sailing-vs-sailing under Rule 12 is a standard probe in RYA Coastal Skipper and Yachtmaster orals; the examiner expects the three sub-rules to be named in order.

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