Hi,I just replaced my prop with a 16 X 16 size, that I had from another boat. It has very wide blades. My engine specs say 4600rpm max. With an empty water tank, 1/4 tank of gas, on a cool morning, engine turned 4800rpm and 37.5 mph. With all the camper cabin canvas up I turned 4500rpm and just over 34mph. I have read that a 14.5 X 17 prop is a possible recommendation also. I am quite happy with this prop and is easily available. I can't try other props as there are no large marinas near by. And unlike the boating mags. say I don't think they would let me borrow props to try, unless I had bought a $50,000 + boat from them.Hope this helps.Argonaut Bill