Well then, to keep it "Simple", change it to 'any spinnaker boat has right of way', period. Then in your scenario, C has right of way over both A and B, and A had just better get out of the way and B can tell A he's got to have room to keep clear of C.
I think giving absolute right-of-way to "any spinnaker boat" will be just as problematic. Imagine two boats sailing downwind. One is clear ahead and not flying a spinnaker. The other is clear astern with chute up. Do you really want to give right-of-way to the astern boat? What about two boats on opposite tacks going downwind? Which one has right-of-way? The starboard boat or the spinnaker boat?
I don't know the history of when and why the "Leeward boat has right of way" rule was written, but I'm guessing whom ever wrote it never envisioned a fleet of spinnaker cats coming downwind at nearly 20 knots...while one boat is going upwind yelling he's got "rights", as if the spin boats can hear him anyway, or can do anything about it, when the puff is on.
Rule 11 "ON THE SAME TACK, OVERLAPPED" derives from the IRPCS, which has roots back to before spinnakers existed and before catamarans were known, so yes, spinnaker catamarans were not envisioned. The basic premise is that the windward boat is most likely more maneuverable, given that the leeward boat may be blanketed.
If your fleet of spin-cats is sailing downwind towards one lone upwind boat... sail around him. It shouldn't be much more difficult than sailing around an anchored committee boat.
If visibility and escape are the problems, then what about a windward cat (flying a spinnaker) with a leeward cat (also flying a spinnaker) in his blind spot? Which one gets right-of-way? How is this situation any different if the leeward boat isn't flying a chute? Why should the rules be different?
No amount of fiddling with right-of-way is going to remove a boat's responsibility for maintaining a lookout. You must know what's in front of you, and plan for how to keep from hitting it.
Regards,
Eric
