Pounding loads from waves and from hull flying, wracking and uneven distribution of bending loads due to waves, deceleration from one hull hitting something, rudder loads and local point loads are all taken into account as well as just the bending loads from either hull flying. The material properties are based on samples we have built and tested. Then there is a safety factor added for all the variables the engineer either cannot control or does not know about. Hence the cost, and the engineer is a lot lower priced than any other as I was his first client, he finds proas fascinating and he knows exactly how little extra information I need.
Rob, are the beam requirements based on the potential need to deal with 100% of the heavier hull (whichever that is - ww or lw) being fully supported out of the water? Are there further factors added such as wave action when the heavier hull is in the air or is there just a safety percentage added to allow for all other factors? If I remember correctly, for you, the action of the windward hull slamming back onto the water was an important consideration - but that was for your hiking platform.
> Assuming the mast is mounted in a hull, the overall boat weights are
> the same and it is a responsible design, the beams on a 60/40 proa
> will be the same as the beams on a 40/60 proa. They will be heavier
> than the beams on a 50/50 and lighter than the beams on a 70/30, a
> 30/70, a 20/80 or an 80/20, etc etc. The upper limit is if the
> windward hull is so small that it is submerged before the boat
> capsizes.