L, M and W are sailing close-hauled on starboard tack. They are approaching an obstruction they cannot safely avoid without making a substantial course change. 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 20.2
(c) 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 20.2
and she shall respond accordingly.
Is M required to hail W for room to tack immediately after 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 20.2
(c) 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, and rule 20.3
permits her to do so even if, in the absence of L, M would not yet need to hail for room to tack. If she fails to hail for room, and as a result is unable to tack as soon as possible, she breaks rule 20.2
World Sailing 2009