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birds mouth boom for bolger bobcat

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  • bobkehoe54
    i was wondering if any of the folks here who have built birdsmouth spars could help me figure out the diameter of my boom for my bolger bobcat......the gaff is
    Message 1 of 2 , Feb 3, 2002
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      i was wondering if any of the folks here who have built birdsmouth
      spars could help me figure out the diameter of my boom for my bolger
      bobcat......the gaff is easy, it's a square...the boom is another
      matter. It is specified as a 1-1/2" x 2-1/2" 13'-6" boom with
      stiffeners on it's sides. i would like to build it round by the
      birdsmouth method. how to calculate??? any idea's would be helpful
      thnx......bobk
    • Derek Waters
      Hi Bob Jim Michalak has a good essay on hollow spars, including calculations for comparing round and rectangular spars. (Feb 00). John O Neill wrote a two part
      Message 2 of 2 , Feb 3, 2002
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        Hi Bob

        Jim Michalak has a good essay on hollow spars, including calculations for
        comparing round and rectangular spars. (Feb'00).
        John O'Neill wrote a two part article on birdsmouth spars for Boatbuilder
        magazine. The Jul/Aug '01 issue has the calculations for elliptical section
        spars.
        Gregg Carlson has a neat program (available at www.carlsondesign.com) for
        calculating strip sizes for round birdsmouths.

        Although a birdsmouth enthusiast, I'm curious as to why you would build the
        boom this way.

        Cheers
        Derek
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