HP calculator for prop size, weight, gear ratio needed

Discussion in 'Powerboats' started by sdowney717, Aug 24, 2015.

  1. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    What I want to know is how much HP is needed for a specified speed say 20 knots, if you have

    Twin engines
    22 by 20 props
    boat weight 17000 lbs
    gear ratio 2.5 to 1
    buttock angle is 4 or 5

    I have yet to find a prop calculator to do that, they all want the engine HP and give you the prop size, I want to go the otherway, to calculate the HP needed to drive the prop.
     
  2. gonzo
    Joined: Aug 2002
    Posts: 13,528
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    Location: Milwaukee, WI

    gonzo Senior Member

    It will depend on the hull size and design. You don't have enough information.
     
  3. sdowney717
    Joined: Nov 2010
    Posts: 852
    Likes: 32, Points: 28, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Thinking of my own boat in particular, 37 foot semi displacement type lobster style hull with a skeg keel and twin engines.

    So I suppose it is 35 LWL and 12 foot beam, weighs 17000 lbs. skeg keel does not extend all the way to the stern.

    I see lots of calculators the can give you a prop size.
    http://www.vicprop.com/displacement_size.php
     
    Last edited: Aug 25, 2015
  4. Easy Rider
    Joined: Oct 2009
    Posts: 920
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    Location: NW Washington State USA

    Easy Rider Senior Member

    Call Michigan Wheel.
    They can be very helpful on the phone.

    Get into boatdiesel.com
     

  5. PAR
    Joined: Nov 2003
    Posts: 19,133
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

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