Rule 12 applies only when two sailing vessels are approaching one another so as to involve risk of collision, and neither is a power-driven vessel. The rule gives way based on which tack each vessel is on, and — when both are on the same tack — which vessel is to windward.
Different tacks
Rule 12(a)(i)Vessel A has the wind on her port side. Vessel B has the wind on her starboard side. Their courses will cross.
Vessel A (port tack) keeps out of the way of Vessel B (starboard tack). "Port gives way to starboard" is the easiest way to remember it.
Same tack, windward vessel
Rule 12(a)(ii)Both vessels have the wind on the same side. Vessel A is upwind (to windward) of Vessel B.
The windward vessel (A) keeps out of the way of the leeward vessel (B) — being upwind gives you more room to bear away, so the rule places the burden on you.
Uncertain which tack the other vessel is on
Rule 12(a)(iii)A vessel with the wind on her port side cannot tell for certain whether another sailing vessel to windward has the wind on her port or starboard side.
She must assume the other vessel has the wind on her starboard side and keep out of the way — Rule 12(a)(iii) resolves the ambiguity by placing the give-way duty on the vessel that is unsure.
This is just a fraction of what the app offers
Download Navitime free on iOS and Android for the full Advanced Navigation book collection, adaptive quizzes, flashcards, and mock exams — all fully offline.