I replaced the transom on my boat several years ago. Aluminum boat with 1 1/4" board in transom for strength. Welded new 1/8" metal for transom with 2 extra gussets at the top and 2 at the bottom. 1 1/2" aluminum angle across top of transom. Glued 1/2" and 3/4" marine plywood together for transom strength. 75 hp motor and no problems.
