> I mean ideally you would have a ww hull as narrow as the lw wouldn't  you?
> I fact why not a 15m ww hull as well?

That presupposes that longer hull = better. That isn't always the case. But it becomes a difficult issue to discuss when the objectives of the various parties aren't agreed upon.

When the HP is sailing full throttle the main hull is being lifted up, and the LW is being pressed down. So relative to drag, how dissimilar are their resistances. relative to longi stability, one can always ask the further question that while one could extend the WW hull waterline length would that weight, slight as it could be, be better spent extending the length of the LW hull which is the one getting tossed around by the rig and various drive action.

It is assume in the Multihull case often, that longer and narrower are always faster. That isn't true of all boats. Boats that are paddled can start to experience increased drag when they assume higher wetted surface areas. Another complex issues with lots of types. While this might not be an issue when heavily driven, I wonder if two equally long hulls will perform as well it light conditions.

There used also to be some stuff about how the proa hulls encounter waves, that suggested that shorter WW hulls where better. I leave that to those who are interested in making the case. What about shunting, is there any advantage there to a shorter hull given the different path it gets dragged through, and rocker.

There is also a lot of posturing on over and under length issues. What waterline length is the length for record, and for comparison purposes. is a Harryproa a 20+ foot boat with a 40' waterline, or a forty foot ama with a really short main hull. What features have been optimized to create what relative benefits.

There is also and aesthetic issue, that is hardly going to be controlling with this type. But proas have traditionally had the shorter WW hull. Presumably nobody cares about that. Most people haven't drunk the Kool Aid, and those that have are not going to be affected by traditional proportions.