How much faster will a 2" pitch change get me?

A 40ph Evinrude w/ 12.5x13 omc uncupped prop gave consistent 24mph on a 600lb fiberglass runabout fully loaded, 3/4 throttle with a tendancy to over-rev.<br /><br />Changing to 15" Hustler prop (cupped)and wondering what sort of speed increase I can expect. 2 or 3 MPH?

Re: How much faster will a 2" pitch change get me?

Could go slower. If you go too steep, the motor won't get up to good RPMs. RPMs mean horsepower. If you're running below the recommended maximum of 5500 RPMs, going steeper only lowers the RPMs more. You'd be getting less than 40Hp. <br /><br />I had a 60 Evinrude on a 15' trihull. With a 17p prop, I had good hole shot and good speed. With a 19p I lost the hole shot and only gained 1 or 2 mph. With a 21p I barely got it out of the hole and I lost speed.<br /><br />What kind of RPMs are you getting now? In general you'll gain or lose 200 RPMs with each inch of pitch change. Going from an aluminum to a stainless would offset that by about a 100. So going from a 13 aluminum to a 15 stainless should drop the full throttle RPMs by about 300.

Re: How much faster will a 2" pitch change get me?

Changing prop pitch one way or the other is always a trade off on one end or the other. (Nearly always).<br /><br />More pitch, less hole shot more top end,(As long as you are still in your top RPM range). less pitch better hole shot, (always) but you have to watch your upper RPMs).But you can go to far and suffer blow out.