small outboard prop question

Discussion in 'Props' started by volkswagen50, May 14, 2010.

  1. volkswagen50
    Joined: Aug 2007
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Holstein, IA. USA

    volkswagen50 Junior Member

    On a small outboard motor, say 5-6 hp two stroke, whats the prop speed vs/engine speed? Are they geared down? Are 4 strokes geared different, I'm thinking that four strokes do not rev as high as a two stroke would at max speed.
    What does a small outboard like that turn for rpm??
  2. Jango
    Joined: Aug 2005
    Posts: 519
    Likes: 7, Points: 0, Legacy Rep: 63
    Location: Mid Atlantic

    Jango Senior Enthusiast

    I believe Max Motor speed for both the 2 stroke and 4 stroke is 4500 - 5500 rpm with 2:1 Gearing. i.e. Prop running half speed
  3. capt littlelegs
    Joined: Apr 2010
    Posts: 237
    Likes: 8, Points: 0, Legacy Rep: -67
    Location: England

    capt littlelegs New Member

    2:1 won't be far out, for example a Yamaha 30 is 1.84:1, the deciding factor is the crownwheel and pinion size in a slim gearbox.

  4. jonr
    Joined: Sep 2008
    Posts: 721
    Likes: 11, Points: 0, Legacy Rep: 57
    Location: Great Lakes

    jonr Senior Member

    Some of the 4 strokes I've seen rev a little higher than the equivalent two stroke.
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.