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Thread: Calculating Weight of a Lead Keel

  1. #1
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    Default Calculating Weight of a Lead Keel

    What is the approximate range in pounds that a lead keel should weigh to support a 50 X 8 mahogany racing sailboat, while offering as little resistance as possible during racing?

    I have a German made sailboat built in 1914. The width of the keel is hard for me to measure but it is 15' long along the boat's hull and its depth (from hull to floor of keel) is 22" tapering to 6".

    I need a general idea so to calculate needs for having the boat moved.

    All thoughts are greatly appreciated.

    Thank you so much!

  2. #2
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    Default Re: Calculating Weight of a Lead Keel

    Lead weighs approximately 605 lbs per cubic foot. If you can calculate the volume of your keel, you should be able to get a pretty good idea of it's total weight.

  3. #3
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    Default Re: Calculating Weight of a Lead Keel

    Quote Originally Posted by Don Kurylko View Post
    Lead weighs approximately 605 lbs per cubic foot. If you can calculate the volume of your keel, you should be able to get a pretty good idea of it's total weight.
    Or 708 pounds or 722 pounds, depending upon where you look it up. I can't for the life of me find any reference to 605 pounds per cubic foot.

  4. #4
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    Default Re: Calculating Weight of a Lead Keel

    Thank you. The problem is how to measure the volume. The Height and Length are easy but the width is curvy. It appears to be about a foot wide at the widest point and about 6" at each end. However it tapers on every side from the widest section. Any ideas how to measure or estimated idea of how many cubic feet there might be?

  5. #5
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    Default Re: Calculating Weight of a Lead Keel

    My reference said 712 lbs. But how to measure width to figure the cubic feet?

  6. #6
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    Default Re: Calculating Weight of a Lead Keel

    I realize that there are specific ways prescribed for such calculations. I'm not looking for specifics. 15' along the hull and 22" from hull to floor tapering to 6" deep in front and 14" in back.
    Does 4 tons sound like too much? Or 2 tons sound too little? My husband had told me 2,000 lbs or 2 tons or was it 4000 lbs or 4 tons? He's no longer with us and I can't remember what he said.
    Thank you so very much!

  7. #7
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    Default Re: Calculating Weight of a Lead Keel

    Rough and dirty. guesstimates from the sizes given

    15' times 1.2 (14") times 0.67 (more than six inches and less than twelve) times 700

    8442 lbs - call it four tons. N.B. this could be a full ton out in either direction.

    AND THAT IS JUST THE BALLAST KEEL.

    If there is going to be a bill from any of these numbers - call a professional and get more accurate numbers.
    Even when they work, they don't work well. I blame engineers.
    The only thing engineers have done to the toaster in the last 80 years is make it disposable. I think it applies to a lot of things

  8. #8
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    Default Re: Calculating Weight of a Lead Keel

    Quote Originally Posted by Bob Cleek View Post
    Or 708 pounds or 722 pounds, depending upon where you look it up. I can't for the life of me find any reference to 605 pounds per cubic foot.
    Oops Typo! Actually should be 708 to 711 lbs per cubic foot, depending on whether it is scrap or pure. According to Chapelle at any rate.

  9. #9
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    Default Re: Calculating Weight of a Lead Keel

    Sorry, but these numbers don't work out to any reasonable amount of lead. The volume based on your estimates of size is just too great. If your husband gave a figure of either 2 tons or 4 tons, I would guess that its 4 tons for a boat of that size and age. With an average ballast ratio of 30% to 40%, that would place the boat displacement at about 13 tons or 10 tons which may be reasonable for such a boat. But that is only a guess.
    Tom L

  10. #10
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    Default Re: Calculating Weight of a Lead Keel

    Perhaps if you know the name of the racing class, or the vessel design would enable someone here to know, or find, the answer.
    (50 feet long x eight feet beam is a specialized craft and it probably has a high percentage of ballast (I wouldn't be surprised at 50% or even considerably more)

  11. #11
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    Default Re: Calculating Weight of a Lead Keel

    Yes, A good description of the vessel will give the folks here a better rough idea of what the keel weighs , rather than a bunch of math problems.
    50 percent or more was normal in the "old days" , not so long ago.

  12. #12
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    Default Re: Calculating Weight of a Lead Keel

    Quote Originally Posted by cklfmba View Post
    The problem is how to measure the volume.
    first you need a really big graduated cylinder. . .

    Quote Originally Posted by cklfmba View Post
    I need a general idea so to calculate needs for having the boat moved.
    If your marina has a Travelift, they may be able to weigh the entire boat for you, while its in the slings. . .
    Simpler is better, except when complicated looks really cool.

  13. #13
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    Default Re: Calculating Weight of a Lead Keel

    "If your marina has a Travelift, they may be able to weigh the entire boat for you, while its in the slings. . ."
    Yer common sense is killin me here

  14. #14
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    Default Re: Calculating Weight of a Lead Keel

    You need to measure the cross section area at each end and half way along its length. I assume that the section is a trapezoid, so the area will be the average width times the height. Make some calipers to measure the width at the top if you need to. You then use Simpsons Rule to work out the volume. To do this you add the area of the ends to four times the area of the mid cross section. Then multiply this sum by half of the length and divide by three. That is your volume. Multiply this by what ever density you believe and Bob is the relative of your choice.
    It really is quite difficult to build an ugly wooden boat.

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  15. #15
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    Default Re: Calculating Weight of a Lead Keel

    Skene's has a section on measuring ballast weight just in case you need further info.
    Jay

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