B and Y are approaching a leeward mark to be left to starboard. When B reaches the zone she is clear ahead of Y. B bears away and at position 2 Y gains a leeward overlap. B maintains her course and a short time later Y needs to alter course to avoid her. Y protests. What should the call be?

Penalize B.

When B reaches the zone, rule 18 starts to apply and Y is required to give B mark-room, which she does. From position 2, B is windward boat and must keep clear of Y under rule 11. B fails to do so and breaks rule 11. The answer is the same if the boats are overlapped at position 1.

Mark-room includes room for B to sail to the mark, but because she is sailing below her course to the mark she is not sailing within the mark-room to which she is entitled and cannot be exonerated under rule 21 for breaking rule 11.