CASE 15        

Rule 12, One the Same Tack, Not Overlapped
Rule 13, While Tacking
Rule 18.1(b), Rounding and Passing Marks and Obstructions: When This Rule Applies
Rule 18.2(c), Rounding and Passing Marks and Obstructions: Giving Room; Keeping Clear: Not Overlapped at the Zone

In tacking to round the mark, a boat clear ahead must comply with rule 13; a close-hauled boat clear astern is entitled to hold her course and thereby prevent the other from tacking.

Question A and B are close-hauled on parallel courses nearing the windward mark with A clear ahead. A expects B, on fetching the mark, to tack to round it for the next mark. Instead, B holds her course, so preventing A from tacking. Has B the right to do this? Answer Yes. While A remains on port tack, B is required to keep clear by rule 12 and, when A enters the two-length zone, by rule 18.2(c) as well. Provided she keeps clear of A, B is entitled to sail any course she chooses, including holding her course. However, if A were to tack, then as soon as she passed head to wind, the boats would be on opposite tacks. Rule 18.1(b) states that rule 18 would cease to apply at that point. In addition, rule 12 would no longer apply, and rule 13 would require A to keep clear of B. RYA 1966/8