Hello, I have a 15 ft. 1972 Aluminum Starcraft with the open bow design. I'm not extactly sure of the model and I can't find a plate on it. It had what I assume was the original motor on it. A 50 hp Johnson. I've owned it for 3 years and the motor just went. The bottom cylinder is junk. My question is what is the largest hp motor that I can put on that boat? Thanks in advance.