Because of that (sound) advice - long ago, LTW will start a new series:
"The (pillow)Case of the Week"
I'll go through the ISAF Casebook 2009-2012 (including changes effective 1 January 2010) starting not at the beginning but at the end and work my way forward. I'll try to publish on Monday or Tuesday, so you'll have a whole week to keep it under you pillow and read it before the Sandman comes.
CASE 113Rule 20.1, Room to Tack at an Obstruction: Hailing and Responding
When a boat hails under rule 20.1 for room to tack, all boats that hear her hail and that will have to respond to give her that room must do so.
L, M and W are sailing close-hauled on starboard tack. They are approaching an obstruction and safety requires them to make a substantial course change to avoid it. The obstruction is not a mark. When the boats are in the positions shown in the diagram, L hails ‘Room to tack’ loudly
enough to be heard by both M and W. When L hails, it is clear that M and W must both tack in order to give room to L, and M does not have room to tack and avoid W.
Does rule 20.1 require W to respond to L’s hail?
Yes. When a boat that is not adjacent to the hailing boat has heard the hail, and will have to respond before the hailing boat is able to tack, she is a ‘hailed boat’ in the context of rule 20.1 and she shall respond accordingly.
Is M required to hail W for room to tack immediately after she hears L’s hail?
Yes, if W is not already responding to L’s hail. Because replying ‘You tack’ is not an option for M in this case, M is required by rule 20.1(b) to respond to L's hail by tacking as soon as possible. Therefore, if M cannot tack because of the presence of W, she must immediately hail W for room
to tack. If she fails to do this, and as a result is unable to tack as soon as possible, she breaks rule 20.1(b).