Can you move your boat back to where the transom is even or just hanging over a little? That way your new transducer wont hit the bunk because it needs to be about 3/8 of an inch below the transom. Go to Wal-Mart or dime store and buy some plastic type cutting boards and glue them together so they are about 1 inch in thickness. Cut them in the shape of your transom and mount it where it covers both sets of holes where the other transducers are. Then mount your new transducer about where the left transducer is now. That way you'll never have to drill in your boat again.