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  1. #16
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    Lake Coochiching, Ontario
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    All things being equal, which they never are, drag is proportional to velocity squared, so speed would be proportional to the square root of horsepower. Except that f=ma, so you need some extra power to actually accelerate to the higher speed. I'd still expect the square ratio to be closer than the cube ratio.

  2. #17
    Join Date
    Oct 2009
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    Gonzales, La
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    Quote Originally Posted by David View Post
    All things being equal, which they never are, drag is proportional to velocity squared, so speed would be proportional to the square root of horsepower. Except that f=ma, so you need some extra power to actually accelerate to the higher speed. I'd still expect the square ratio to be closer than the cube ratio.
    That's exactly what I thought a few years ago, before being corrected by someone on another forum.

    Drag force is proportional to speed squared. However, power is a function of force x speed, so speed gets in there one more time making it speed cubed. Here's a good read:

    http://phors.locost7.info/phors06.htm

    The actual equation is here, showing velocity cubed:

    http://www.gtechprosupport.com/support/AeroDragCalc.htm
    Last edited by engineermike; 11-10-2012 at 10:20 AM.

  3. #18
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    Nice!

  4. #19
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    Jan 2008
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    Hello
    I was lucky enough to have the oportunity to Check a 250HO on my boat.
    Top speed went from 70 to easy 76 mph but with a little difficult sea conditions!
    With better sea conditions i think that i could go to 77/79 mph.
    The only problem is that the 250HO is borrowed from a friend of mine so i have to take it out of my transom.

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