Quick Keel Bolt Question

Discussion in 'Sailboats' started by LTDboatdesign, Jun 24, 2013.

  1. LTDboatdesign
    Joined: Oct 2010
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    Location: Bainbridge Island WA

    LTDboatdesign Junior Member

    I am calculating the number and size of keel bolts I will need for a boat i'm designing. What i'm wondering is if I use say 3/4in bronze and I have threads cut into it on both ends, can I still consider it a 3/4 in bolt or should I calculate the area remaining at the valleys of the threads. I am using Nevins rule of 1 sq. in per 1500 lbs of ballast.

    Thanks for the help.
     
  2. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Use the minor thread diameter. It's not so much the reduction in area, but the stress concentration at the thread root. So for 3/4-10 UNC 2A, minor dia is 0.6255; for 3/4-16 UNF 2A, minor dia is 0.6718.

    Remember to have at least 5 threads or 1 diameter engaged. Torque depends on what the internal thread material is. Also you should figure out the SM of the bolting pattern and look at the moment; really important for narrow fin keels without flanges.
     
  3. LTDboatdesign
    Joined: Oct 2010
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    Location: Bainbridge Island WA

    LTDboatdesign Junior Member

    Thanks, thats what I suspected, but its good to be reassured. Well written reply, thanks so much.

    Cody
     

  4. Petros
    Joined: Oct 2007
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    Location: Arlington, WA-USA

    Petros Senior Member

    this is normal to use the minor dia, plus a safety factor for the stress concetration, for bolts in tension. if the bolt is in shear than you use the full diameter assuming the full diameter is at the mating/shear interface. On a keel you possibly have both shear and tension, the one that dominates determines the size and number of bolts.
     
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