CALL UMP 19              

Rule 17, On the Same Tack; Proper Course
Definitions, Proper Course

Question
Nearing the end of the downwind leg, the boats are overlapped on starboard tack. Yellow has established an overlap to leeward from clear astern, is governed by rule 17 and is sailing her proper course. Soon her proper course will be to gybe for the mark. When must Yellow begin to bear away to gybe?

Answer
Yellow must begin to gybe at the time she would have borne away to gybe if she had been sailing with no other boat nearby. If she clearly delays beyond that time, she will break rule 17 by sailing above her proper course.