My 1975 18sf has a factory 20" transom. The guy I bought it from said I needed to raise the transom for sure. He had a Yamaha 100 four stroke on it and he had big issues with self bailing and following seas. I dont have a motor yet but I am looking at a 2004 Johnson 150(391 lbs. dry). I am redoing mine right now. I am closing in the transom and putting a bracket with 26" setback and a full platform on it. My drains are going out the sides of the boat in front of the full width transom box. This will put the drain holes about 15" or more from the stern. I am also going to raise the floor, but Im not sure how high I should come up with it
. I want it to self bail in a hurricane if possible. I hope with the full transom I wont have to worry about the following seas to much.