Originally Posted by srm
How can P be required to keep clear of S AND S be required to give P mark-room? If you look at the definitions, those appear (to me) to be mutually exclusive requirements.

The two are not mutually exclusive. S must give P enough room at the mark so that P can sail the course without S having to take avoiding action. If S does not give P mark-room, and as a result S must act to avoid P, then S breaks rule 18.2(b) and P breaks rule 10. It is entirely possible for both boats to break a rule. In this instance, however, provided P is sailing within the mark-room to which she is entitled, she is exonerated under rule 21 for breaking rule 10 or 31.

I hope that helps,
Eric