I have a 15-4 Gheenoe with a Nissan 9.8 2 stroke short shaft. My cavitation plate is 2-1/2 inches below the bottom of the hull. I want to make a riser plate to bring the motor up. The question is, how high? If I build a riser plate (with no setback) can I raise the motor 3-1/2 inches so the cavitation plate is an inch above the bottom? On another similar question, if I build a jack plate, is there a rule of thumb that I can use that says for every X inches of setback I can raise the motor another X inches?