what is the ideal RPM at WOT?

[mikeyzx2]

This question gets asked alot but it never pertains to my motor so I gotta know. It's a 1977 Evinrude 85hp, pushing a 17-foot Astroglass. The prop is 13 1/4 X 17, which means it's a 17 pitch right? Theoretically what RPM's should I be turning with that prop, and what should my motor be running at WOT? And what kind of MPH could I expect out of this setup? I'll be taking notes.......

 

[walleyehed]

Re: what is the ideal RPM at WOT?

the RPM will be determined by the weight and drag of the boat, as well as engine set-up, mounting heigth, Type of prop and altitude at which you operate, not to mention the general condition of the engine itself.<br />There is no "Theory" to what RPM it should turn....the "Theory" is how far the prop moves the boat fwd in one revolution of the prop.<br />WOT should be above 5500 and 5700-5800 would be a good target with a normal load.<br />"If" we are in the 5500 RPM range, your speed would be "close" to 38-39MPH...Just a guess figuring 12% slip, but we don't know that without a WOT reading from you.<br />Tons of variables here.