Tacking at windward mark to starboard

And the boats fitted all this in within the two hull lengths zone?

Wow.

OK, here goes.

@ Position 1

A is right of way boat (rule 12) entitled to mark-room (rule 18.2( b )).

B is keeping clear and giving mark-room.

@ Position 2

B is right of way boat (rule 11), limited by rule 15 (must initially give A room to keep clear).

A is still entitled to mark-room (rule 18.2( b )), sailing within the mark-room to which she is entitled and thus entitled to exoneration under rule 21 if she does not keep clear.

@ Position 3

When B, in tacking, passed head to wind, rule 18 ceased to apply (rule 18.1( a ) or ( b )), and A's entitlement to mark-room ceased.

B, having been the give way boat until she reached her close hauled course (rule 13) is now the right of way boat (rule 10), limited by rule 15.

So the only rules applying are rules 10 and 15.

@ Position 4

A keeps clear.

When, in tacking B passed head to wind,

·         she became the give way boat (rule 13), and

·         rule 18 again began to apply, and

·         because B passes head to wind in the zone, its rule 18.3.

When B reaches her close hauled course inside A:

·         she becomes the right of way boat (rule 11),

·         bound by rule 18.3( a ) to not cause A to sail above close hauled.

@ Position 5

Whatever B 'asks' for, she has no entitlement to room of any kind.  With rule 18.3 on, rule 18.2 does not apply (rule 18.3 stem) and B, becoming inside boat does not get an entitlement to mark-room under rule 18.2( a ).

In a rule 18.3 situation, if the fetching boat is above the layline, by any significant amount, it's going to be unlikely (although not impossible) that she will be caused to sail above close hauled in breach of rule 18.3( a ), even though she may need to change course to windward.  The test for rule 18.3( a ), first bit, is that she is caused to sail above close hauled, not just to 'head up'.

If it wasn't definite whether or not A sailed above close hauled, at the last point of certainty, she was not sailing above close hauled, so she should be taken to be not sailing above close hauled.

A is keeping clear, not sailing above close hauled.

B is right of way boat, not entitled to mark-room, not breaking rule 18.3.

No rules broken.