Today’s rule is the last rule in Section B.
17 ON THE SAME TACK; PROPER COURSE
If a boat clear astern becomes overlapped within two of her hull lengths to leeward of a boat on the same tack, she shall not sail above her proper course while they remain on the same tack and overlapped within that distance, unless in doing so she promptly sails astern of the other boat. This rule does not apply if the overlap begins while the windward boat is required by rule 13 to keep clear.
Proper Course
A course a boat would sail to finish as soon as possible in the absence of the other boats referred to in the rule using the term. A boat has no proper course before her starting signal.
Clear Astern and Clear Ahead; Overlap
One boat is clear astern of another when her hull and equipment in normal position are behind a line abeam from the aftermost point of the other boat’s hull and equipment in normal position. The other boat is clear ahead. They overlap when neither is clear astern. However, they also overlap when a boat between them overlaps both. These terms always apply to boats on the same tack. They do not apply to boats on opposite tacks unless rule 18 applies or both boats are sailing more than ninety degrees from the true wind.
Rule 17 is talking to both the ROW boat and the Keep Clear boat. If you establish a leeward overlap from clear astern of a Windward boat, and within two hull lengths, then the Leeward boat may not sail above her proper course while that overlap continues and any part of her boat is within the two hull length. The Windward boat is always obligated to keep clear of the Leeward boat. However, the Leeward boat is limited to sailing at or below what would be her proper course in the absence of the Windward boat. Leeward’s proper course is a course she would sail in the absence of Windward to finish as quickly as possible. You must also be aware that if the overlapped boats were required to steer a course around other boats, the proper course for the leeward ROW boat could be very different from a Proper Course in the absence of other boats. There is an exception to the ROW requirement not to sail above her Proper Course, which is that the leeward boat may sail above a proper course, if as a result she sails clear astern of the Windward boat. A question that is often asked by the Windward boat is, can the the ROW Leeward boat force the Windward boat to pass head to wind. The answer is yes. If the Proper Course for the ROW boat on a beat to windward and is close hauled and is pointing higher than the windward boat can, as long as the leeward boat is sailing close hauled, the windward boat must keep clear. If keeping clear requires the Windward boat to tack, she must tact. A good way to tell if a Leeward ROW boat has sailed above close hauled on a close hauled proper course, is when her sails start luffing. Luffing sails are not the fastest way to sail around a course! It is important that the Windward boat understands that her one and only job is to keep clear of the ROW boat. If the Windward boat believes that the ROW boat broke a rule, protest her, but be sure to continue to keep clear.