If umpiring in that situation, one might, if at all, declare '15 good'; which is to say that the keep clear boat has room to change course in either direction without immediately needing to avoid contact with the ROW boat. So, technically 15 is complied with. However, 17 does apply and, in the situation described, the leeward boat may luff as she pleases, as long as, while she is changing course, she gives the windward boat room to keep clear.

Thanks Ant.
Ant Davey

Said Created: Today 13:30

Does not apply?

Writing up the findings, one may include 'Rule 17 applies' insofar as the overlap was established from more than 2 hull lengths to leeward, so luffing was permitted. Or, no, it doesn't apply. That would depend on what the leeward boat did after establishing the overlap.

Ant, you're stating that backwards.  You mean to say rule 17 does not apply -- that rule begins with "If a boat clear astern becomes overlapped within two of her hull lengths to leeward of a boat on the same tack," which is not true in this case.  I don't think protest committees should state rules that don't apply unless there's some issue with whether a specific rule applies or not. In this case, if the boats later converge and W is protesting that L sailed above her proper course, then I agree, the fact that rule 17 did not apply should be in the Conclusions.  

Surely it's like a number of situations: the rule applies, but has no practical effect. Same as starboard still has ROW over port when they're half a mile apart and not on a collision course.