Will my prop be over pitched?

Discussion in 'Outboards' started by valvebounce, Oct 19, 2022.

  1. valvebounce
    Joined: Dec 2010
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    Location: manchester uk

    valvebounce Senior Member

    I have a 2000yr 25hp johnson with a 10" dia-13"pitch prop on it.
    The boat is a 14ft broom speedboat with a planing hull.
    As an estimate I would put the weight at 1800lbs (average weight with load)
    The boat is fibreglass.
    I am contemplating putting a 15"pitch prop on it.It would obviously take longer to get out of the hole,
    but I am wondering if it will still reach it's WOT speed.
    I am trying to avoid buying the wrong prop and wasting my hard earned cash.
    I am 50 miles from the sea,and over here in the UK there are definately no fresh water venues where there are no speed limits.I'm in Manchester UK,and all the rivers are restricted locally.
    The draft on the boat is about 7".Pointed bow with an almost flat stern.
    Anyone got any ideas?
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    What are the RPMs at wide open throttle (WOT) right now?
     
  3. valvebounce
    Joined: Dec 2010
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    Location: manchester uk

    valvebounce Senior Member

    Hi Gonzo,the revs are pushing 5500-5800 at full throttle.
     
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    bajansailor likes this.
  5. valvebounce
    Joined: Dec 2010
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    Location: manchester uk

    valvebounce Senior Member

    Thanks Gonzo,the outboard is a two cylinder.
    Looking at the chart the wot for a two cylinder should be 4500-5500.
    The engine has good compression and not a lot of hours on it.
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    In that case you could even go to a 17".
     

  7. valvebounce
    Joined: Dec 2010
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    Location: manchester uk

    valvebounce Senior Member

    Many thanks for your advice Gonzo
     
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