Sorry I don't know how to post a picture here but hopefully the explanation will do. 2 boats approaching top mark, both on starboard, overlapped, but neither is making the mark when they enter the 3 boat length circle. As they are on same tack, rule 18 applies as they enter - right ? But who is the inside boat ? WW boat is closer to the mark but LW boat is usually considered inside. They both have to tack to make the mark, does Rule 18 turn off when they tack ? If they both tack and stay overlapped, can the previously LW boat (now WW and definitely inside boat) claim room as if they had originally entered the circle on port ? If the overlap is broken as they tack, can the original WW boat deny room to the other boat ? As they approach the mark on starboard, does LW boat have any rights i.e. is it the inside boat ? Or can the WW boat sail right up to the mark and tack at the last second - effectively pushing LW boat past the mark on downwind side.