Flotation calculations

Discussion in 'Wooden Boat Building and Restoration' started by Kaptin-Jer, May 12, 2012.

  1. Kaptin-Jer
    Joined: Mar 2004
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    Kaptin-Jer Semi-Pro

    Can someone give me a link that will help me calculate bouyancy? I was able to stuff 1,500 cu. ft. of foam into my boat and I
    Want to try figure how that translates into bouyancy.
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Buoyancy calculation are straight forward. So long as you use consistent units.

    For example.

    In SI units (which I use) the units of density or kg/m^3, or in words kilograms per cubic metre. So this means how much does a block of 1.0m x 1.0m x 1.0m weigh?

    So we can write this as the density = mass/volume.

    Once you understand this buoyancy calculations become easy.

    Fresh water has a density of 1000 kg/m^3. Which means one cubic metre of fresh water weight 1000kg. For sea water it is 1025kg/m^3.

    So if you have a material that has a density greater than 1000 kg/m^3, is shall sink, in fresh water. If it is less, it shall float.

    You may find this simple video link useful:
    http://www.ehow.com/video_4980167_calculate-buoyancy.html
     
  3. Kaptin-Jer
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    Kaptin-Jer Semi-Pro

    Thanks. Very helpful link. I might even learn something
     
  4. Kaptin-Jer
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    Kaptin-Jer Semi-Pro

    Oops 15 not 1,500.
     
  5. DCockey
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    DCockey Senior Member

    Sea water is approximately 64 lbs/cubic foot. Fresh water is approximately 62.3 lbs/cubic foot. The buoyancy will equal the weight of the amount of water displaced, so the if the 15 cubic feet of foam are fully submerged they will provide 960 lbs of buoyancy in sea water. But if the foam is not fully submerged then the buoyancy will be less.

    When the foam was added to the boat the weight of the boat increased so the additional weight needs to factored in.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Yep, I was about to jump all over Jer with what new, huge project he was tinkering with, you use 93,000 pounds of buoyancy foam.

    15 cubic feet of foam, is about 934(ish) pounds of buoyancy, less of course the weight of the foam. If it's the typical 2 pound pour in foam, then 900 pounds of floatation has been added.
     
  7. Kaptin-Jer
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    Kaptin-Jer Semi-Pro

    Thanks Par. You know the boat I'm building. It looks like I'm on the plus side of neutral. Not ready to share pics yet, but I'm on the down side of the build. Just have to add the pretty stuff like all the teak trim and teak deck (yes I added a foredeck) Still thinking about asking for your help in cutting a mast if I can't find one. I'll let you know.
    Jerry
     
  8. PAR
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    PAR Yacht Designer/Builder

    No sweat, just give be a yell.

    When preforming floatation calculations, think worst case if you have the internal volume for it. You'll want the crew, skipper, Fidel the wonder dog, the cooler full of beer and other important stuff, able to sit in the boat, while completely swamped, reasonably level and still have some freeboard left, so you can bail you brains out.
     
  9. Kaptin-Jer
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    Kaptin-Jer Semi-Pro

    Yep, did all the calcs and found out I have to leave the wife home.
     

  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    That's what soap operas are for . . .
     
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