Ok ill try to include as much info as I can, im new to boats. My boat is an alumacraft 1442 flat bottom riveted jon, I have a 1980 evinrude 15 hp in good condition, but needs a prop. The boat is 230 lbs, so wieght is between 930 lbs max and probably 550 minimum for boat, motor, gear and people, I use the boat around 5000-7000 feet above sea level. It currently has a badly worn and chinked 9.5x10 prop, and with a total weight of 570 about, the best speed I got was 16-17 mph, bumping up to 18 once or twice on my gps, and with about 680 and with wieght shifted around for best speed we got up to 13 mph, and with a max load, we were down to about 6-7 mph, and I dont have a tachometer (need to get one) What I would like is a good estimation on size/pitch/3 or 4 blade, as to have a good prop mostly for higher speeds, and being able to reach the best top speed with the heavier loads. I dont go out much alone, so generally it will be in the mid to upper load levels, with seldom use in the lower end. I REALLY appreciate any information, this is a fun project my father and I are going in on. thanks again