Prop selection

[JEllwanger]

17 ft fiberglass ski/pleasure with Johnson 1960 75hp. Current prop 10 diameter 11 pitch 3 blade aluminum. What effect does pitch up or down have on performance in general? I can tow a couple of kids on a tube without any trouble, but I may be looking for a little more top end when fishing.

 

[Navigator]

Re: Prop selection

What RPM does your engine turn at WOT (Wide Open Throttle)? You need to make sure you stay within the operating range as per the manufacturer.<br /><br />Expect a 200 RPM drop for each 1 inch increase in pitch. Ideally, you'd want to be at the high end of the range with the boat empty and the low end of the range when fully loaded. <br /><br />Run your boat fully loaded and then empty to get the RPM range and then you can see if changing the prop will help. If the current pitch is the best you can do, them you might want to consider a Stainless Steel Prop. An SS prop should give you slightly better top end because the blades do not flex as much as the aluminum.<br /><br />Worst thing you could do is "overprop". Then the engine can never reach its designed operating range. This will cause all sorts of issues and will eventually damage the powerhead.<br /><br />Good luck.

 

[JEllwanger]

Re: Prop selection

Thanks. I don't have any way of knowing what my RPM at WOT is, I have the original service manual and should be able to get the recommended RPM range, but I can't directly measure it under load. The plugs I took out were in good shape according to a local boat shop dude, so I am guessing the previous owner might have dialed it in reasonably close. The whole rig only cost me $1150.00, so if I even get a summer or two out of it I'll be happy.