RRS Rules that Apply
Rule 10 applies if two boats are on opposite tacks, Rules 11 and 12 apply if they are on the same tack.
Rule 10 is the familiar Port and Starboard situation where the starboard tack boat will have right of way.
Rule 11 applies for the overlap of two boats, one of which is beating to the mark and the other has rounded the mark and is going downwind. The downwind boat is to windward of the beating boat and so must give way
Rule 12 applies when the two boats are not overlapped. They both need to stay clear of each other until an overlap exists then the leeward boat has right of way subject to rule 15 and 17.
Rule 15 says the boat acquiring right of way has to give the other, burdened, boat a chance to keep clear. ie: Leeward boat can't come up immediately after acquiring ROW through an overlap
Rule 17 says that when overlapped and within two boatlengths of another boat to windward, the leeward boat shall not sail above her "proper" course. The "proper" course was presumed to be the direct course to the mark but it could be whatever the fastest way around the course is so it could be not directly at the mark.