Have been playing with the float shape for the last few nights. Im trying to pick how flat i want the bottom. the flatter the bottom the earlier it will plane but when the boat is lacking power ( Open 8.5's have a restricted sail plan) it will be pushing the extra wetted surface area though the water making it slow in light winds.a semicircle bilge has the smallest wetted surface area making it easily driven when not planing. Its hard trying to pick where on the spectrum will be optimum for your sailing conditions .
most of the new tri designs have very round bilges on the floats ( seacart 30 , seacart 26 , multi 23, exploder 25)

here is what i have created so far i like the look of it but i have a lot of fine tuning to get the hull shape correct
LCB will be between 56% and 58% and the LCB of the floats will be forward of the LCB of the main hull by around  300mm. the floats will be flat out planing hulls with wave piercing bows  and the main hull will be very round to reduce wetted surface area.

hello
i am hoping to design, build my own trimaran in my shed on a budget.
the boat will be designed to the New Zealand Open 8.5 class http://www.multihull.org.nz/
and will need to be competitive in the class, be built on the cheep and have room in the main hull for cruising.

now the fun begins