Predicting speed for a given prop hp

Discussion in 'Hybrid' started by Stumble, Jun 10, 2016.

  1. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Due to a whole new crop of electric conversion threads I have been trying to find a way to predict the speed of a hull with a given amount of hp applied at the prop. Basically a spreadsheet where you can enter basic boat information and it will kick out an aproxamate amount of power needed at displacement speed for a standard monohull sailboat (the ability to predict a cat as well would be nice).

    Does anyone have something simple that can acomplish this?
     
  2. gonzo
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    gonzo Senior Member

    Any of the basic design books has that. Kinney, Gerr, etc. The power required is irrelevant of source. This nomograph works well.
     

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  3. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You took it from Nicholson's "Boat Data Book", right? :)
    It is one great book, one of the most odd ones I've had - but definitively very useful.
     
  4. gonzo
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    gonzo Senior Member

    Yes, I think that is where it came from. I've had that for years. It is surprisingly accurate.
     
  5. Stumble
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    Stumble Senior Member

    Gonzo,

    I appreciate the chart, but I have absolutely zero idea how to read it. Is there a guide to it somewhere?
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    That is the example. If you follow the lines. Start with the length and make a line crossing the displacement until it intercepts the right baseline. From that point, make a line intercepting the HP until it crosses the left baseline. From that point make a line to the B/D of the shape type of your boat. That last line crosses the speed line on the expected speed of the boat.
     

  7. Stumble
    Joined: Oct 2008
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    Location: New Orleans

    Stumble Senior Member

    Got it, thanks.
     
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