CALL UMP 17              

Rule 11, On the Same Tack, Overlapped
Rule 16.1, Changing Course
Rule 17, On the Same Tack; Proper Course

Question 1
Yellow and Blue, close-hauled on port tack, approach the layline near the windward mark. Yellow established her overlap from clear astern. Both sail beyond the layline and are clearly overstanding the mark. Yellow luffs, and is then forced to bear away to avoid contact. There is a Y flag. What should the call be?

Answer 1
When Yellow luffs it is clear that her only proper course is to luff in order to tack toward the mark. Yellow gives Blue room as required by rule 16.1. Yellow is then unable to sail her course without the need to take avoiding action. Blue does not keep clear and breaks rule 11. Penalize Blue.

Question 2
What would the call be if due to shifty winds and/or rough seas it is not clear whether the boats are overstanding the mark?

Answer 2
It is not yet clear that her only proper course is on the other tack. Yellow breaks rule 17 by sailing above her proper course (close-hauled). Penalize Yellow, unless as a result she falls astern. See also Call UMP 9.