(This is an instalment in a series of blogposts about the ISAF Casebook 2009-2012 with amendments for 2010. All cases are official interpretations by the ISAF committees on how the Racing Rules of Sailing should be used or interpreted. The cases are copied from the Casebook, only the comments are written by me.)
(Case 42 has been deleted in the Casebook)
Rule 12, On the Same Tack, Not Overlapped
Rule 19.2, Room to Pass an Obstruction: Giving Room at an Obstruction
If an obstruction can be passed on either side by two overlapped boats, the right-of-way boat, if she chooses to pass it to leeward, must give room to the other. If the right-of-way boat chooses to pass it to windward, she is entitled to room to do so, and the other boat must keep clear. There is no obligation to hail for room at an obstruction.
Boats BL and BW, overlapped on the starboard tack, are overtaking Boat A, also on the starboard tack but moving more slowly. Rule 17 does not apply between BW and BL during the incident.
Does rule 19 apply between BW and BL as they overtake and begin to pass A? If so, which parts of it apply and when do they apply?
At positions 1 and 2, rule 12 requires both BL and BW to keep clear of A. Therefore, A is an obstruction to both BL and BW. However, A is not a continuing obstruction, as the last sentence of the definition Obstruction makes clear.
As BL and BW overtake A, BL may choose to pass A on either side (see rule 19.2(a)). When either BL or BW begins to pass A, provided that they are still overlapped, rule 19.2(b) will apply.
If BL chooses to pass A to leeward, rule 19.2(b) will require her to give room to BW, as inside boat, to do likewise if BW steers a course to do so.
However, BW is not required to take the room provided, and may pass A to windward, keeping clear of her under rule 12 and then rule 11. If BL chooses to pass to windward of A, then rule 19.2(b) requires BW to give BL room to pass A and rule 11 requires BW to keep clear of BL.
Rule 12, and later rule 11, require BL to keep clear of A.
Does BW have to hail for room to pass to leeward of A? If not, would BL risk disqualification by not giving room?
BW is not required to hail for room, although that is a prudent thing to do to avoid misunderstandings. Rule 19.2(b) requires BL to give room to BW if they both pass to leeward of the obstruction, whether or not BW hails for room.
The Right-of-Way boat (BL) has the right to choose not the keep clear boat. A misunderstanding many sailors struggle with. Only when it is clear that BL will pass to leeward, can BW go in and expect to be given room. Provided that there was an overlap and BL is able to give room from the moment the overlap is first established.
BL cannot move sideways, so if BW only gets an overlap at the very last moment, she’s taking a big risk.