Posts: 3514
Location: Elk River, Minnesota | Hiya,
Sounds like your motor was over pitched to begin with using the 14 pitch as when you switched to the 12 you gained speed. My guess is your motor has a gear ratio of 1.85:1, so the 12 is probably good for just you, but would still be too much pitch for essentially 4 guys in the boat (with the 350 lb man).
Nothing is wrong with your motor...you just need a lower pitched prop for the boat when you load down. When you pitch up or pitch down in a prop, each inch of pitch is roughly worth 200 RPM. When you change diameter, each 1/4" is roughly worth 100 RPM. so...when you went down to a 12 pitch from your 14 (+400rpm) and went up in diameter 1/4" (-100rpm), you essentially gained 300 RPM overall. So...you gained some performance overall.
My suggestion: Get a 10 pitch propeller and see how that works. With the amount of weight you are trying to push, I would not be surprised if you are unable to get the boat to plane out... You are in a situation where I believe you are reaching the limits of the rig, and nothing but either a) a larger motor, or b) replace the entire rig are your options to gain performance with the kind of weight you are carrying.
Steve |
