Five boats were approaching a leeward mark dead before the wind. Four of them were overlapped in line with A nearest the mark. The fifth boat, E, was clear astern of A, B and C when those three boats reached the zone. When D came abreast of the mark and turned to round it, E became overlapped inside D. This occurred after E had already reached the zone and before D reached it. E rounded the mark behind A, B and C but inside D, which was able to give mark-room to E.

Was E entitled to mark-room under rule 18.2(a) from D?

Yes. Because E was clear astern of A, B and C when they reached the zone, she was required by rule 18.2(b) to give each of them mark-room. Between E and D, however, a different relationship developed. In order to leave room for the three inside boats with their booms fully extended, D had to approach the mark on a course that brought her abreast of it outside the zone. When E reached the zone, she was clear astern of D and D was still outside the zone. Therefore, rule 18.2(b) did not apply between D and E. When D changed course towards the mark, E obtained an inside overlap and rule 18.2(a) began to apply between D and E. E was entitled to mark-room under that rule, which D was able to give.