The transom ?? what do you intend for the splash well . Needs to be small and fast self draining . if a wave poops in the back you could sink the boat . 2 waves and you are history !! think long and hard . small splash well less water so wont weight the back of the boat down !,need to be just big enough for the motor and a small amount of clearance each side thats all . Could even bracket the motor and push it back far enough and have no splashwell at all would be even better will make the boat go better as well !!