Wouter-
In Michigan at the Cat Fight I attended there had been a lot of wind which had the whole "great lake" to build across and then steepen of course as they got to the other shore which is where the races were being held. They were more like the wakes from large powerboats than wind driven waves (IMO). At one point the wind actually got fairly light even though the waves were still high (to me- 3-4 foot but steep and short troughs) and this made it tough going upwind since it was hard to get the boat driving between waves and I wasn't able to fly a hull (figured out in Tampa I had way too much prebend and spreader rake so was running a really flat sail). Lots of pitching and tough to tack. Reaching was tough because the waves were such that one hull was at a crest while the other was in the trough then the wave sort of climbed between the hulls with the crest burying the tramp and beams (very slow trying to drag all that through the water). Downwind in the lighter air was fine but when the wind had been heavy it was crazy- bear up, get some speed start rocketing down the short wave surfing and then the lee bow would enter the wave ahead as the upwind stern "planted itself" in the wave behind and the hulls would try to suddenly slow down but the sails were still trying to go faster than the wave- Sort of would "submarine" through the wave ahead, as started to get clear would accelerate and surf into the back of the next one. The BIM 16 had the same "issues" in the conditions and chose not to fly the spinnaker since this only seemed to give our "twin hulled submarines" the "DIVE, DIVE!!" command. Except of course if one doesn't blow the ballast tanks (ie if the boat doesn't fill with water but stays full of air) the "periscope" with attached sailcloth quickly passes the rest of the "submarine" and the crew has to abandon ship.
It occurred to me once or twice that if one were to really "heat it up" and go wild basically trying to go very fast at a fairly high angle (for downwind- or even upwind for that matter) one might come out ahead of the "submariners" but maintaining the boat "wild" under these conditions while constantly steering over the waves was more than I was ready for at that time. (Heck, were "lucky" to get 2' waves on my local lake if the fetch is the entire lake!)

Kirt