Terry, did the rudders feel heavy when this happened? I've had mine stall out when trying to bear off quickly in a puff (going downwind) but no problems going upwind. A quick wiggle of the tiller (unload the rudders) will re-attach the flow.

I have also had them cavitate but only on a blast reach, going very fast on one hull. It felt like I had hooked a trash bag with the low rudder but when I looked down there was just a huge air bubble where the rudder was, it was hard to move the tiller, I had to ease the main, slow down a little to get the flow back on the blade. This would also happen on the I 20 first generation rudders quite a bit.