The mystery of a proper prop and terrible performance.

Discussion in 'Props' started by missinginaction, Jan 25, 2020.

  1. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    I didn't express myself very well. Those high back helm seats weigh 40 pounds each. The dink about 70. So it's 150 pounds for all three items, not that it matters. You have me thinking though.

    I know where the water line is. The boat's in the yard. I should be able, without too much difficulty, to calculate the volume of water the hull displaces. Long ago, in the late 70's I passed Calculus III. I don't remember a lot of it today but there are methods of calculating displacement when you don't have a scale. Might be a worthwhile winter project.

    We'll see.

  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    My pleasure, anything I can do to assist.

    However, without sounding like a broken record (showing my age with that comment), i simply cannot state clear enough, you need to know the actual true weight of your vessel and where possible, depending upon how you obtain the weight, the current LCG in the lightship condition.
    Everything starts knowing these values; without which it is pure speculation and assumptions that could all lead down the wrong track and wasted time/money.
    missinginaction likes this.
  3. 7228sedan
    Joined: Nov 2009
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    7228sedan Senior Member

    Glad to see the update MIA.
    I can certainly attest to the benefit of tabs, at least on mine. I cannot think that won't be the missing link to getting her over the hump! I definitely 2nd what Fall Guy recommends as well. Strip her bare as a test and add weight back as you go after the tabs are added.
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you have an accurate waterline, it is not too difficult to calculate the weight; just tedious. Divide the submerged volume into small sections and add them up. Multiply by the density of water ~64 lb/cu ft.
  5. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Yup. The smaller the sections the better the estimate. I remember finding the area under the curve in math class all those years ago. I'll have time to do an estimate over the winter. Based on my observation of the boat when it was recently under full throttle, I'll bet that she's not too far over 7,000 pounds. But the math will tell us.


  6. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    I've been told by people smarter than me that it's easiest to jack it up corner at a time, and weigh it that way. I didn't get to that, because I imagined the travel lift could tell me. Nope. Serenity was too light to get a good read, but then my problem was never going to be weight, it was always going to be hydrodynamic.
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