i have a 1979 bassmaster 15 ft fiberglass boat with a 1979 mercury 80hp on it . i run a stainless 13 dia. 21 pitch and i get about 40 mph out of her. loaded down i only loose about 5 mph. she dosent run wide open rpm's but jumps out the hole and uses very little gas. i go through about 4 gallons on an all day fishing trip. i think this is about the best combination. i also pull the kids on a tube from time to time. hope this helps