Hmm. Wouter, what I THINK you`re saying is that if you widen a boat`s beam you put more load on the leeward hull in strong breeze, perhaps so much that the bouyancy of the leeward hull is not enough to support the additional load, so the whole hull starts to submerge, never mind the bow ?
So in order to take an existing design & widen the platform, first you would need to re-design the hulls to have more bouyancy in general, preferably with a healthy percentage of it up front, unless the hulls are very bouyant to start with. So in effect you start again, and design a complete new boat. There has to be a limit as to how much width you can put on an existing hull design. Making a Hobie 16 wider will only increase the distance you fly after that inevitable pitch-pole !

Steve