Propeller sizing...

[Sean Herron]

Hello...

Just bought a used (120 hrs) 8 horse long leg Evinrude for my O'day 22 - it has a 12/8 prop on it and pushes me to hull speed at less than half throttle...

Guy I bought from used as kicker on a planing power craft...

Lots of wash on the rudder - motor on good bracket to starboard of rudder and prop rotates clockwise - when I open it up the wash gets ridiculous and some vibration sets in...

I mic'd the shaft - was never hit - I think going to a 10/7 will help and I have a dealer who 'just happens to have one on the shelf' - yeah for how long and why...

Smaller diameter - more rpms (better for motor) - mid pitch - good push...

Before I lay out for the prop what do you guys think...

Thanks in advance...

[artemis]

If you're up to hull speed at half throttle then you are not effectively using the HP you have - i.e., you've got too much for the size prop you're swinging.

I'd suggest using a larger diameter prop - if possible. This is the best way of "using up" HP. You'll then probably have to adjust pitch. David Gerr has some excellent prop calculations in his "The Nature of Boats".