help to design an 18ft inboard cat

[floydrob]

hi, i'm going to atttempt to build my own custom catamaran. i have a 60Hp inboard and limited space, so 18ft is as big as i can go. will do double skinned for strength and would like a small cuddy/cabin. just a pleasure craft, odd weekend away etc.
need to be able to use in relatively bad conditions as the weather here isnt all that great most times!.

my current idea is to have 2 hydroplaning hulls, with a raised bow and then a single shallow hull in the middle that will barely touch the water and rise out the water when on the plane. the engine will be situated midships for best balance and make it much easier to get up on the plane.
the cabin will be pretty low for a sleek sporty look with an aerofoil shaped roof. thats as far as i am at the moment.

any tips? ideas? plans i can work from for the hull?
thanks, robert