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Thread: Prop selection for optimum cruising vs top end

  1. #1
    Member Maast's Avatar
    Join Date
    Mar 2008
    Anchorage, Alaska, United States

    Default Prop selection for optimum cruising vs top end

    After I boogered up my last prop I went and got a solas 17 pitch to replace my Yam OEM 17 pitch prop. I lost 500 RPM (dropped to 5k vs 5.5k) but my WOT speed is about the same (within 1 MPH)
    However, at my 4500 cruising RPM I've gained 5 MPH and my MPG seems to have gotten better, I can't tell for sure since I dont have a fuel flow meter.
    I'm pretty happy with the increase in speed and MPG at my cruising RPM but I'm worried I'm lugging the engine by being underpropped.
    On the other hand I never run WOT for more than a min or two, sucks too much gas.
    Also, I'm puzzled by the RPM change even though both props are 17 pitch.

  2. #2
    Member theultrarider's Avatar
    Join Date
    Mar 2009


    Props are alot like tires. Not all 12.5x35 inch tires will measure exactly that! Some 35's are closer to 33. Some 36. Same with your prop. You switched brands. Maybe even material too??? In either case, you should be able to reach your engines max rpm/redline when at wide open throttle with a normal load in your boat. This will give you your best all around operation. I am guessing your redline is 6000 and you are only getting 5000. That is not good. You will not that if you ever get in big water. You will be missing your bottom end hp where you need it the most.

  3. #3
    Join Date
    Apr 2006


    Don't let any notion or discussion of "propping for power" or "propping for speed" sway the fact that your engine needs to run at the top of its rpm range with a normal load. Any fewer rpms, and you are overpropped, simple as that.

    In stainless props, I've observed that the amount of cupping on the trailing edge of the prop blades can vary drastically from manufacturer to manufacturer. This can profoundly affect how the prop behaves. You might have lucked into a new prop with a heavy cup, and it's not letting your engine run as it should.

  4. #4
    Member atvalaska's Avatar
    Join Date
    Nov 2007
    camp-go-4-beer fbks

    Thumbs up

    put your "normal" weekend load in your boat....not your moose hunting load! If the maker of the motor sayz its to run 5000-5800 rpm at full speed...the prop u need will run the high end of (ie; 5600+rpm). If to much rpm lower pitch, if to little rpm raise the pitch. u can cup and uncup your own prop with a hammer and a little work, and see what that gets u.

  5. #5

    Default If it was that easy

    Boat loading, center of balance, trim all play a roll, there is no one factor, they all add up. sure prop has a big big roll, but same prop with added weight up front or back is going to act different.
    X-USGC Ballast Control Master


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