Cruising Catamaran

I am working on a design for a power catamaran that is intended for use mostly in shallow protected coastal waters with an occasional fair weather trip to the Keys or Bahamas.

It is LWL 30', Beam 11'-10", draft 1'-5" (full load) twin long shaft, 115hp 4 cycle outboards. Take a look at attached photo of scale model.

I am striving for max fuel efficiency at cruise around 16 knots. The current plan is for sawn frames at 32" o/c, 2x6 keelson, 2x4 bottom ribs and 2x3 side ribs with two layers of 1/4" ply, epoxied together with fiberglass exterior.

Can anyone out there help me or direct me to information to be sure this is adequate? I have tried Gerr, but results seem ridiculous, but I may be applying formulae incorrectly. Also not too sure about roll stability, and pitch causing prop cavitation in weather.

 

Photo didn't attach. I think operator malfunction occurred.