2 layers of 18mm marine ply glued together then the whole transom area glassed in then the lot veneered over with strip planks that are 18mmx...
thanks guys the vertical sides of the tunnel are 2 layers of 20mm marine ply lapped to give strength length ways the rest like a laminated beam...
I'am building my dream a 8.5 mtr long x 2.4 mtr wide x 1mtr to 1.2 mtr high hull with 10 deg x 500 wide sponsons . with a 1 mtr wide tunnel...