Two new Q&A's were published by the ISAF Q&A panel:
Q&A 2010 -011 about how to interpret overlap with one of the boats having a bowsprit overhanging the stern of the other boat.
Q&A 2010-012 about rule 18.3. One boat forcing the fetching boat above close hauled, after having been subject to rule 13 in the zone.
The principle in Q&A 2010-011 is used for umpiring. The point of last certainty dictates the decision. And that does not change until a next certainty is reached. The rule-book also uses the same principle in rule 18.2(d).
Now for those of you who want to do a little digging:
Suppose the boat with the bowsprit establishes an overlap to windward, then swings the bowsprit over the stern of the other boat until it has an overlap to leeward. Does the leeward boat have a rule 17 restriction? Can she sail above her proper course?
Q&A 2010-012 is pretty straightforward. The crucial words in the rule are: "causing the other boat to sail above close hauled". If that is the case it does not matter that the fetching boat already had to do that to round the mark or not. If the tacking boat was the cause, she breaks rule 18.3.