I am confused by rule 18 and what defines the zone at the finish line. The question is in relation to whether a boat must give another boat room to cross the line (ie. finish). Rule 18.2 a and b seem to apply at finishes, so at the finish line of a downwind finish, would the "zone" be 3 boat lengths from the pin, the signal boat or the closest part of the line? Rule 18 applies between boats when they are required to leave a mark on the same side and at least one of them is in the zone.