Using an Outboard Comparison site - hull weight question

Discussion in 'Powerboats' started by rwatson, Sep 6, 2014.

  1. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    I am using this terrrific web site
    http://outboards.findthebest.com/

    for finding the best power/weight performance on a project
    http://www.boatdesign.net/forums/boat-design/28ft-trailer-sailer-20-knots-under-power-51338.html


    It makes it really easy to find motors that have the right HP/weight combination.



    But, one of the selection options is called "Recommended Boat Weight"

    What do you think the implication of that option is ?

    Would using a motor on a heavier hull mean lower engine life, or what ?

    For example, if the theoretical calculations show the correct HP/Engine weight figures fit, are we just talking about slower acceleration times ? or are there more insidious side effects do you think.
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    A realistic assessment of what your cruise speed is going to be, would be the starting point in engine selection, imo. The actual weight difference between engines of similar hp would only be an issue if there is a peculiarity of the hull that makes it sensitive to extra weight at the stern, which would mainly be the case if the boat is relatively narrow.If your cruise speed was down around 15 knots, I would be looking at engines that turn larger diameter props than normal for the engine hp, which usually also involves greater gearbox reduction ratio. Whatever the case, the engine must be able to rev freely, well into the manufacturer's recommended range, with the propellor pitch selected. That way, regardless of the weight of the boat, you won't hurt the engine, even if the performance disappoints.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member


  4. rwatson
    Joined: Aug 2007
    Posts: 5,839
    Likes: 276, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

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