Tony Mooney, of Sydney, Australia, sent me the diagram at right and asked how the rules applied at each position in it. Andy and Becky are running directly downwind on a leg from the windward mark to the leeward mark. The buoy shown marks the outer edge of an anchoring area, and the sailing instructions require boats to leave it to starboard. Therefore, the buoy is a mark according to the definition Mark.

Throughout the incident Andy is on port tack and Becky on starboard. Normally the defined terms clear ahead, clear astern, and overlap do not apply to boats on opposite tacks. However, since 2009, these terms do apply to boats on opposite tacks that “are sailing more than ninety degrees from the true wind” (see the definition Clear Astern and Clear Ahead; Overlap). Therefore, at all times Andy is clear ahead, Becky is clear astern, and the boats are not overlapped. So, you might well ask, “Which boat has right of way? Becky as the starboard-tack boat or Andy as the boat clear ahead?” The answer requires you to pay attention to the introductory “when” phrases in Rules 10 and 12. Rule 10 does apply because the boats are on opposite tacks. Rule 12 does not apply because, even though Andy is clear ahead and the boats are not overlapped, they are not on the same tack. Therefore, Becky has right of way, and she retains it throughout the incident.

Just afer Position 2, when Andy’s hull reaches the zone, Rule 18 begins to apply. Because Andy is clear ahead at that moment, Becky is required by Rule 18.2(b) to give him mark-room. According to the definition Mark-Room, Becky must give Andy space to sail a direct course to a position at which the mark is alongside the starboard side of his bow (Position 3). Then she must give him room to sail his proper course while “at” the mark. In this case, his proper course is simply to sail straight on towards the leeward mark. Andy is entitled to sail to the mark and then straight past it even if Becky must change course to avoid him while he is doing so. If Andy were to break Rule 10 while sailing to and past the mark in that manner, he would be exonerated under Rule 18.5.

When Andy is past the mark and on his proper course to the leeward mark¸ he no longer needs mark-room and so Rule 18.2(b) no longer places any obligation on Becky. However, Andy remains obligated under Rule 10 to keep clear of Becky. Andy should immediately take action to avoid breaking Rule 10. He could jibe, which would switch off Rule 10 and switch on Rule 12, giving him right of way. Or he could luff or bear away so that Becky could continue on her course with no need to avoid him.

In the situation described to me, Andy does not do either of these things. At Position 4, Becky’s spinnaker brushes Andy’s backstay. Andy breaks Rule 10 by failing to keep clear and if protested he would be disqualified. Both boats break Rule 14 by failing to avoid contact when it was reasonably possible to do so. As the right-of-way boat, Becky cannot be penalized for breaking Rule 14 unless the contact causes damage or injury (see Rule 14(b)).