That is tough to answer as it depends upon the boat, the horsepower, the ratio of the drive. We have on our blog and in our newsletter
(marinepartsexpress.com) a nice write up on prop sizing that might be useful.
Typically every inch you go up in prop pitch, you drop the RPMs by about 250 RPMs or so. Now if you are under propped now (you can get
up to wide open throttle very easily and/or bump against the delimiter that keeps the engine from overreving) then you can go with
a bigger prop. If on the other hand, you can’t up to the WOT (wide open throttle) RPMs then you could be over propped.
The key aspect to remember is that the prop size does effect the speed of the boat, but the bigger the prop (or the smaller the prop) doesn’t
necessairy mean the boat will go faster (or slower). It is all a balance of the variables.
If you send me the length, width and weight of the boat along with the ratio of the drive, I can put the data in my program and see what the program
recommends for prop size.
J. D. Neeson
Marine Parts Express
Toll Free: (877) 621-2628
International: (207) 882-6165
Fax (207) 882-9865
Our blog: blog.marinepartsexpress.com