Propeller sizing...

Discussion in 'Boat Design' started by Sean Herron, Oct 26, 2004.

  1. Sean Herron
    Joined: May 2004
    Posts: 1,520
    Likes: 32, Points: 58, Legacy Rep: 417
    Location: Richmond, BC, CA.

    Sean Herron Senior Member

    Hello...

    Just bought a used (120 hrs) 8 horse long leg Evinrude for my O'day 22 - it has a 12/8 prop on it and pushes me to hull speed at less than half throttle...

    Guy I bought from used as kicker on a planing power craft...

    Lots of wash on the rudder - motor on good bracket to starboard of rudder and prop rotates clockwise - when I open it up the wash gets ridiculous and some vibration sets in...

    I mic'd the shaft - was never hit - I think going to a 10/7 will help and I have a dealer who 'just happens to have one on the shelf' - yeah for how long and why...

    Smaller diameter - more rpms (better for motor) - mid pitch - good push... :?:

    Before I lay out for the prop what do you guys think...

    Thanks in advance...
     
  2. artemis
    Joined: Oct 2004
    Posts: 410
    Likes: 15, Points: 0, Legacy Rep: 267
    Location: USA

    artemis Steamboater

    If you're up to hull speed at half throttle then you are not effectively using the HP you have - i.e., you've got too much for the size prop you're swinging.

    I'd suggest using a larger diameter prop - if possible. This is the best way of "using up" HP. You'll then probably have to adjust pitch. David Gerr has some excellent prop calculations in his "The Nature of Boats".
     
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.