I think that Jake is right on about why the rule is such. Image if you are the starboard boat and know you are about to be used as a pick? You have to be more than a little bit nervous. The upwind starboard boat is Queen Bee to all but a leeward boat on the same tack. Downwind they are almost Queen Bee, Princess maybe. They should not have to worry about the real possibility that there will be a boat coming over their stern because the rights are fuzzy.
There are three things that can happen at this intersection.
First is that the leeward boat can decide to tack to starboard. In this case the windward boat is obligated to tack due to obstruction.
Second is that if the leeward boat decides to go behind the starboard boat they are required to give room for the obstruction (starboard) to an overlapping windward boat.
Third is that the leeward boat goes behind and the windward boat tacks under starboard. Too many things can happen in this scenario if there are other boats in proximity. One respondent mentioned, there may be other port boats to weather that do not have time to get out of the way if this boat has to do a slam tack.
You have to consider the safest scenario of all. That is the way the rules are made.
Later,
Dan
Sorry, bit late into this one, but Dan has it nailed.
The windward port boat has rights to room to avoid the stb boat if the leeward boat decides to duck the stbd (and he must take it if he asks for it).
The leeward port boat has the right to ask the windward port boat for room to tack to avoid, but if he asks for it, he must take it. The port boats cannot use this situation to break a windward cover or boat pinching up under you situation. If you ask for room to avoid or tack then you must take it. If you ask for room to tack, you expect the other boat to tack almost instantly (within reason of course)
or call "you tack" and then the windward boat must avoid the (tacking onto) stbd boat; if the windward boat does not think this is appropiate(the calling for water to tack), they must still tack (or call "you tack") and then protest (don't have the case to hand). Ditto the leaward boat.
Now the only thing I cannot find is what happens if both boats call for "room to tack" and "room to avoid" at exactly the same time....... The must be a case somewhere on it !
