Section II – Conduct of vessels in sight of one another
Rule 12: Sailing vessels
(a) when two sailing vessels are approaching one another, so as to involve risk of collision, one of them shall keep out of the way of the other as follows:
(i) when each of them has the wind on a different side, the vessel which has the wind on the port side shall keep out of the way of the other;
(ii) When both have the wind on the same side, the vessel which is to windward shall keep out of the way of the vessel which is to leeward;
(iii) if the vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether the other vessel has the wind on the port or the starboard side, she shall keep out of the way of the other.
(b) For the purposes of this Rule, the windward side shall be deemed to be the side opposite that on which the mainsail is carried or, in the case of a square-rigged vessel, the side opposite to that on which the largest fore-and-aft sail is carried.