Giving room at an obstruction (rule 19) requires overlap. Room to tack at an obstruction (rule 20) does not.

mini,

Any chance you can draw up a diagram of the situation? Would make things much more clear. In my reading of the situation, Boat 2 would be at fault for not giving boat 1 room to duck boat 3 (assuming they were overlapped after both tacked). I don't see any reason to penalize boat 3- they were a starboard tack boat.

The correct thing to do would have been for boat 2 to pass the hail up the line to boat 3, then boat 3 would have obligations as outlined in rule 20.