(This is an instalment in a series of blogposts about the ISAF Case book 2009-2012 with amendments for 2010. All cases are official interpretations by the ISAF committees on how the Racing Rules of Sailing should be used or interpreted. The cases are copied from the Casebook, only the comments are written by me.)
Rule 12, On the Same Tack, Not Overlapped
Rule 13, While Tacking
Rule 18.1(b), Mark-Room: When Rule 18 Applies
Rule 18.2(b), Mark-Room: Giving Mark-Room
Rule 18.2(c), Mark-Room: Giving Mark-Room
In tacking to round a mark, a boat clear ahead must comply with rule 13; a boat clear astern is entitled to hold her course and thereby prevent the other from tacking.
A and B are approaching the windward mark which they are required to leave to port. They are close-hauled on parallel courses with A clear ahead. A expects B, when she can tack and fetch the mark, to tack to round it and head for the next mark. Instead, B holds her course as shown in the diagram and sails on well past the mark.
Has B the right to hold her course in this way and, thereby, prevent A from tacking?
Yes. While A remains on port tack, B is required to keep clear by rule 12 and, as A was clear ahead when she reached the zone, B is required by rule 18.2(b) to give A mark-room as well. Provided B keeps clear of A and gives A mark-room if A luffs (even if A luffs as high as head to wind), B is entitled to sail any course she chooses, including holding her course.
However, B is no longer required to give A mark-room after A leaves the zone (see rule 18.2(c)). If A were to pass head to wind, then at that moment all parts of rule 18 would cease to apply because the boats would be on opposite tacks (see rule 18.1(b)). In addition, A would no longer have right of way under rule 12, and B would become the right-of-way boat under rule 13.
One solution for Boat A to get out of this situation is to time his luff so that she will have enough speed to get head to wind next to the mark. Boat B will either have to luff and end up on the wrong side of the mark or bear down to behind A. If the latter happens boat A can safely tack while keeping clear.
Boat B bears off behind A. She’s not entitled to mark-room although she get’s an inside overlap in position 3. RRS 18.2(c), first part.
Boat B luff and finds herself on the wrong side of the mark. She can’t continue upwind to interfere with A, because A is already on the next leg and that means boat B would break rule 23.2.
She can also start pinching as soon as she’s entered the zone clear ahead to get closer to the mark that way. In both scenario’s boat B has to keep clear and has to give mark-room (until A passes head to wind_
Boat B slows down between 2 and 3 to go behind A. And A can continue as lead boat, although she has lost some speed in doing so. The one thing boat A must not do is pass head to wind before boat B has committed to go behind. Rule 18.2(c), second part, also states that mark-room is lost once the boat having mark-room passes head to wind.