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Thread: Yamaha 25 prop question

  1. #1

    Default Yamaha 25 prop question

    We've got a 25 Yamaha 4-stroke on a 16' jon. I have 2 props for it; one is a 9-7/8 x 9 and the other is a 9-7/8 x 10-1/2. Which prop/pitch will give me better top end? Last year we ran it with the 9" pitch with the boat loaded with stuff and 3 big guys and it ran okay. This year there's only 2 of us and won't be so loaded.

  2. #2
    Member SusitnaAk's Avatar
    Join Date
    Feb 2007


    I think the high no# the more speed, I know when you lower the No# More weight , Front no# diameter tail,No# pitch is what i,m talking about. Give a Boat shop a call Make sure, hopes this helps

  3. #3

    Default Understand Props
    should help,
    diff pitch for loaded or not
    Diff for HP to Boat weight ratio's

  4. #4

    Default Hey Piranha,

    Thanks for that link! It really helped me understand what I was looking at doing; only problem is that the 25 has no tach, so I don't know if we're even in the right RPM range with either prop. Hmmmmm....
    I saw a link a while back to Cabela's that had a small external mounted RPM meter for any small engine; I'll check into that and see if I can get this rig dialed in.
    One more question: the way the motor is mounted on the transom, the cavitation plate is about 2-3" lower than the bottom of the boat; is that correct?
    Thanks again,

    Just ordered the Tiny Tach from Cabela's; I'll post how everything works out!
    Last edited by Big Jim; 07-21-2008 at 13:36. Reason: added info

  5. #5
    Member MARV1's Avatar
    Join Date
    Jul 2006


    Cavitation plate should be flush or 1/2" lower than the bottom of boat. Raise the motor up and you'll gain in speed a bit.
    The emphasis is on accuracy, not power!


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