How would you decide this?

Dave Perry’s 100 Best Racing Rules Quizzes highlights specific aspects of the racing rules in a fun format designed to help you become more familiar with The Racing Rules of Sailing. Here is one of the quizzes:

Quiz 39
Boats PI, on port tack, and SO, on starboard tack, are sailing dead downwind bow to bow approaching a leeward mark to be left to port with PI on the inside. When a length from the mark, PI bears off slightly so that she can round the mark leaving it to port without touching it. The booms of the two boats make contact with no damage or injury. SO hails, “Starboard!” and PI hails, “Room!” Both boats hail, “Protest!” SO rounds the mark behind PI. Neither boat takes a penalty.

You are on the protest committee…how would you decide this? Answer below.

Quiz 39 Answer:
Boat SO is disqualified. When Boat PI reached the zone, the boats were overlapped. Boats on opposite tacks are “overlapped” when rule 18, Mark-Room, applies between them or when both boats are sailing more than ninety degrees from the true wind. In this case, rule 18 applied between them and they were both sailing more than ninety degrees from the true wind.

Rule 18.2(a)(1), Giving Mark-Room, requires an outside overlapped boat to give the inside boat mark-room, which is the space the inside boat needs to sail to and around the mark in a seamanlike way (see the definitions Mark-Room and Room). SO failed to give PI that space and broke rule 18.2(a)(1).

PI broke rule 10, On Opposite Tacks. However, as she was sailing within the mark-room to which she was entitled, she is exonerated (freed from penalty) by rule 43.1(b), Exoneration, for her breach of rule 10.

It is possible that both boats could have avoided the contact, in which case each broke rule 14, Avoiding Contact. But because SO was the right-of-way boat and PI was sailing within the mark-room to which she was entitled, they are each exonerated by rule 43.1(c) as the contact did not cause damage or injury.

Source: US Sailing