What is gear reduction ratio in typical outboard motors ?

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

  1. preventec47
    Joined: Jul 2016
    Posts: 22
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Atlanta, GA

    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
    Joined: Aug 2016
    Posts: 18
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: ID

    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
    Joined: Aug 2002
    Posts: 15,500
    Likes: 1,040, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,394
    Likes: 1,024, Points: 113, Legacy Rep: 702
    Location: Australia

    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
    Joined: Nov 2003
    Posts: 19,133
    Likes: 489, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    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
    Joined: Sep 2016
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SE MI

    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
    Joined: Aug 2002
    Posts: 15,500
    Likes: 1,040, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Which ones?
     
  8. hoytedow
    Joined: Sep 2009
    Posts: 5,812
    Likes: 374, Points: 93, Legacy Rep: 2489
    Location: North of Cuba

    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
    Joined: Jun 2009
    Posts: 1,302
    Likes: 273, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Suzuki
     
  10. gonzo
    Joined: Aug 2002
    Posts: 15,500
    Likes: 1,040, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Thanks, it is an interesting solution.
     

  11. Steve W
    Joined: Jul 2004
    Posts: 1,824
    Likes: 63, Points: 48, Legacy Rep: 608
    Location: Duluth, Minnesota

    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.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.