What is gear reduction ratio in typical outboard motors ?

Discussion in 'Outboards' started by preventec47, Aug 14, 2016.

  1. preventec47
    Joined: Jul 2016
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    preventec47 Junior Member

    Maybe the ratio changes between mfgrs and among models with the
    same mfgr. I want to analyze my propeller performance and I have
    to know how fast the prop is spinning at different engine rpms.
    I am primarily focused for now in the range of 10 to 40 hp.
     
  2. Dieboat
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    Dieboat Junior Member

    From my research and based on zero real experience, the gear sets in outboard motors range between 1.47-1.92. It appears that the higher ratios usually correspond with more horsepower; my information comes from the manufacturers sheets of higher horsepower outboards.
     
  3. gonzo
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    gonzo Senior Member

  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I doubt you'll find 1.47:1 or close to it, back in the days before through-hub exhausts they were lower than now, but 2:1 is a pretty standard ratio today, with typically the ratio dropping as hp size increases.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Yeah, 2:1 is typical with 2:5 reserved for high thrust applications. Subtle variations do occur, probably just to be different, but 2.09:1 and 2.47:1 don't really count much in the big picture.
     
  6. theoldwizard1
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    theoldwizard1 New Member

    Some high horsepower outboard, especially 4 stroke, have gear reduction immediatly under the power hear at the top of the leg.

    This helps keep the foot more hydrodynamic.
     
  7. gonzo
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    gonzo Senior Member

    Which ones?
     
  8. hoytedow
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    hoytedow Carbon Based Life Form

    My Honda 9.9 has a gear ratio of 2.33 to 1. The prop turns once for 2.33 crankshaft revs.
     
  9. baeckmo
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    baeckmo Hydrodynamics

    Suzuki
     
  10. gonzo
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    gonzo Senior Member

    Thanks, it is an interesting solution.
     

  11. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    My Yamaha 9.9 high thrust has 2.92:1 reduction, about as low as I have seen, even Yamahas other high thrust offerings are not that low.
     
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