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Thread: Prop help

  1. #1

    Default Prop help

    Hi guys, me again asking about our 25 hp 4 stroke Yamaha.
    Thanks for the help with my oil change question. Now I've got another one:
    I have 2 aluminum props for the boat (16' Xpress jonboat).
    The boat currently has the 9-7/8 x 9 prop on it.
    The extra prop I have is the 9-7/8 x 10-1/2.

    What's the difference and which one will give me better holeshot & top end?
    We're loading the boat with 3 big ugly guys (all over 200 lbs.) and a bunch of stuff (rods, 11 gallons gas, cooler, etc.) Which brings me to another question:
    How come they don't make boats big enough? With the boat on the trailer and cleaned out, looks likes there's loads of room in there!
    Thanks,
    Jim

  2. #2

    Default Both

    The 9 will give you hole shot, and the 10.5 will give you top end. The problem is you sacrifice one for the other.
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  3. #3
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    Default

    Quote Originally Posted by Big Jim View Post
    Hi guys, me again asking about our 25 hp 4 stroke Yamaha.
    Thanks for the help with my oil change question. Now I've got another one:
    I have 2 aluminum props for the boat (16' Xpress jonboat).
    The boat currently has the 9-7/8 x 9 prop on it.
    The extra prop I have is the 9-7/8 x 10-1/2.

    What's the difference and which one will give me better holeshot & top end?
    We're loading the boat with 3 big ugly guys (all over 200 lbs.) and a bunch of stuff (rods, 11 gallons gas, cooler, etc.) Which brings me to another question:
    How come they don't make boats big enough? With the boat on the trailer and cleaned out, looks likes there's loads of room in there!
    Thanks,
    Jim
    The first number is the diameter of the prop and the second is the pitch. The pitch refers to the distance traveled forward during one complete revolution.
    So your 9" pitch will travel 9" while the 10.5" will travel 10.5", theoretically. This does not account for any prop slip. To answer your question, if the props are both the same diameter, the lower the pitch, the greater the hole shot. And your 10.5" pitch prop will give you better top end. To see which prop works better for you you need to know your wide open throttle RPM's with your given load. Yamaha wants it to be in the upper half of the recomended range, so if the recomended range is from 5000-6000rpm you should be running at 5500+ rpm's with a full load. Less than that and you will be lugging the engine. Hope this helps.
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