what size outboard for 14ft ply hydroplane

hi, i have just made a 14ft hydroplane from plywood and tyhe covered in fiberglass, the [plans i am following rate the hull to a 50hp engine, though i recon it would rip the thing apart with thrust and all the forces acting on the transom, not just the weight, thats been sorted. my mate and i sat on the transom when it was in the water and she sat fine, that was much more weight that a 50hp outboard, but the forward backwards and sideways forces must have some kind of negative effect , what size engine shud i use, and if u live in scotland, can u sell me 1 for a good price?