Top speed with 18hp Evinrude on 14′ aluminum

[garry-in-michigan]

OK – file the back side only of the leading edge of the propeller to bring it to a knife edge. Make sure all blades are the same to keep it in balance. Cut a yardstick into three pieces and stack them between the motor and transom. Make sure the motor is securely clamped, then check the speed. If it ventilates on turns. take one piece out. . . 😉
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[stephenspann27]

good idea on the yard sticks

[stephenspann27]

The prop is 9” diameter and 10” pitch. I’d like to prop it down a bit to handle more weight. I removed about 150lbs of weight from the boat and went from 15mph to 19mph. I think it was a difference of about 400RPM. Should I go down to a 9×9 or try a 9.25×7? I’m running about 4,450RPM in "light form and about 4k, to 4,100RPM in semi loaded form. Max hp is at 4,500 RPM, but max RPM is 5,0000.

[stephenspann27]

Bump…

[david-bartlett]

Stephen,
I have run about 6 different 18’s over the past 45 years. I have run most of those hours with a 9 X 9 prop and a few with a 9 X 10. All on 14 foot aluminum boats except for some use on a plywood 14 footer.

Unless you have a real light boat with a light load, I think you will be much happier with the 9 X 9.

The 18 is no racer but will go fast enough for what it was designed for. They don’t seem to like being overpropped.

JMHO.

[stephenspann27]

Thanks David, I’ll give the 9×9 a try.

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