Blue and Yellow are both on starboard tack in the prestart. Blue is clear ahead and farther to windward than Yellow. From position 1 and onwards, Yellow holds her course and sails forwards, and Blue sails backwards without any course change. Just before position 3, an overlap is established and immediately thereafter there is a contact.

Both boats Y-flag. What should the call be?

Penalize Yellow. While Yellow is clear astern of Blue, she is required to keep clear under rule 12. Shortly before position 3, Blue has a need to take avoiding action and therefore Yellow breaks rule 12.

When Yellow becomes overlapped with Blue and acquires right of way, Blue has no possibility of keeping clear. Therefore, Yellow does not initially give Blue room to keep clear and breaks rule 15. Blue is exonerated under rule 21(a) from her breach of rule 11.

The fact that Blue is sailing backwards does not change the situation. Sailing forwards or backwards through the water is not an ‘action’ within the meaning of the second part of rule 15. Therefore, rule 15 requires Yellow to initially give Blue room to keep clear.