Question
X and A are both close-hauled on port tack when X reaches the two-length zone of a port-hand windward mark. X is clear ahead of A. X luffs to tack around the mark, but the presence of A prevents X from tacking and X protests. What should the call be?

Answer
Because X is clear ahead when she reaches the two-length zone, A must keep clear of her until they have rounded the mark unless X passes head to wind. This applies even when A becomes overlapped inside X: A must still keep clear and has no right to room. However, if X passes head to wind, rule 13 applies and rule 18.2(c) no longer does. Also, while the boats are on opposite tacks on the beat, no part of rule 18 would apply.
X may therefore luff to head to wind and A must keep clear of X which she does. No penalty.