While racing, boats AW and BL are approaching an obstruction that can be passed on either side. Both boats are heading towards the middle of the obstruction. At position 1, AW is clear ahead by a very narrow margin and on a track to windward of BL. At position 2, they have become overlapped with AW to windward of BL.

At position 1, AW is clear ahead and thus has right-of-way under rule 12. When the overlap between them begins, BL becomes the right-of-way boat under rule 11.

Rule 19.2(a) states that the right-of-way boat may choose to pass the obstruction on either side. How can we determine which boat has the right to choose in this situation?

At any point in time, the right-of-way boat at that moment is entitled by rule 19.2(a) to choose on which side she will pass the obstruction. Therefore, while AW is clear ahead of BL, she has the right to choose to pass the obstruction on either side. When the boats become overlapped, AW loses that right, and at that time BL has the right to choose.

When a right-of-way boat acts to implement a choice she has made under rule 19.2(a), she must comply with any applicable rules of Sections A and B. Rule 19.2(b) applies if the boats are overlapped. In that case, the outside boat must give the inside boat room between her and the obstruction, unless she has been unable to do so from the time the overlap began. Rule 21(a) applies while the inside boat is taking the room to which she is entitled under rule 19.2(b).