Prop for lightweight 15.5 ft runabout / 40 HP outboard

Discussion in 'Props' started by Peter.D, Nov 10, 2014.

  1. Peter.D
    Joined: Nov 2014
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    Location: London

    Peter.D New Member

    Hi, what propeller would you suggest for lightweight plywood boat (about 550 lbs - boat+engine+fuel) with 40 HP Yamaha outboard engine? I'm currently using Solas - Amita 3, aluminum 3 blade prop with 11 diameter and 15 pitch and gaining speed about 30 knots. My expectations were about 35 - 40 kn...
    I was trying to use prop calculators like propcalc etc. and the resulting prop is 11/23. But this pitch seems to me out of the normal range... What prop should I try?
    My basic data are: 40 HP with max 5500 rpm, 2.0 gear ratio, 700 lbs (incl 1 man), 13 ft LWL, 35 kn required speed, C ... 170 (just guessing - between runabout and fast)
    => prop 11/23... ???
    Thanks for any suggestions.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    What RPM do you get at WOT?
     
  3. Peter.D
    Joined: Nov 2014
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    Peter.D New Member

    Don't know yet. I'll get tachometer by the end of this week so let you know afterwards. It seems that I gain max speed on cca half open throttle and then it doesn't accelerate anymore. I'll do more testing when I get tachometer and write back. Just to let you know - this boat has 7 deg deadrise - for flat water and trim is about 1-2 deg at full speed.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    That seems like an over-propped motor. The tach will let you know.
     

  5. sandhammaren05
    Joined: May 2009
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    Location: Texas & Austria

    sandhammaren05 Senior Member


    With 2:1, 5500 RPM, 36 mph, you need 15" pitch. The required diameter is 10". Solas produces bad designs if you want speed. Also, I once bought a Solas and the pitch was 2" less than advertised! I'd buy a Turbo or Stiletto, both designed by Jim Booe in Indianapolis. The company is still run by Jim's son but was bought by Yamaha. And forget aluminum.
     
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