The boat that tacked in front of me can get to a close hauled course (and not be moving at all?) and then I would still have to avoid them?
Yes. The boat that tacked does not have to be moving, nor do her sails have to be set. Once she is pointing in the direction of a close-hauled course, her tack is complete.
I left the part out about how we were about to round A mark:
If the port boat tacks in the zone, then Rule 18.3 places an addtional requirement on her. Not only does she need to give the starboard-tack boat that is fetching the mark room to keep clear, she must also give that boat mark-room (if starboard passes inside) and not cause that boat to sail a course above close-hauled (if starboard sails above her). If the starboard boat has to sail above close-hauled, or is prevented from passing the mark properly, then the tacking boat breaks Rule 18.3.
I hope that helps,
Eric
