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Lofting of Perigee

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  • Don Douglas
    Happy Holidays to everyone! I have started lofting the lead keel section of Perigee. Currently I have 1050 lbs of clean lead from tire weights (need 1400
    Message 1 of 2 , Dec 24, 2007
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      Happy Holidays to everyone!

      I have started lofting the lead keel section of Perigee. Currently I
      have 1050 lbs of clean lead from tire weights (need 1400 lbs). So I
      decided to make my mold for the keel. I plan on lofting the lower
      center section around the lead keel and making mold patterns to strip
      plank the form for the mold. This strip planked form will get faired
      inside and re-inforced outside. I am only lofting sections 2-8 from
      the base to LWL. That omits 2 stem sections and 3 aft; 2 load lines
      and the sheer. Tight on space until after Christmas.

      Here is my dileema. I know the table of offsets will need some
      correcting and am ready for that. There were two points along the
      bottom of the keel that were out by 3/8". The batten does not lie
      and when drawn to the table of offsets, the line was very unfair.
      The half-breadth plan for waterlines 1, 2, 3 are fair as are the
      buttock lines 1 and 2 through this central section. So on to the
      body plan. Waterlines and buttocks here match up nicely but if I try
      to put in the diagonals...no luck, they are all out.

      I have rechecked my grid (fisrt time my waterlines were off by 1/4"
      so out with the paint and a new canvas), verified all vertical and
      horizontal measurements, verified the half-breadths and heights at
      waterlines and buttocks, etc. All the diagonals are out by at least
      1/2" or more. If I refer to the lines drawing from the plans, I am
      more confused. But I am not going to scale off from the lines to
      verify anything. Would probably cause more errors and I don't have a
      5/8" = 1' scale nor can I find one.

      Has anyone had this type of problem with Atkin's Table of Offsets on
      other plans? For me, I am rereading Chapelle and Vaitses, maybe I am
      missing something.

      May warmer days be in your forecast
      Don Douglas
      Colorado Springs
    • alankornhauser
      I have never lofted an Atkins design full-scale, but I have entered the offsets for a few flat- and vee-bottom designs into various computer programs. I ve
      Message 2 of 2 , Dec 24, 2007
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        I have never lofted an Atkins design full-scale, but I have entered
        the offsets for a few flat- and vee-bottom designs into various
        computer programs. I've found several clear errors in the offset
        tables from MotorBoating articles. I suppose the MotorBoating
        articles were produce on a pretty tight schedule, and the scaling off
        the lines drawings was not done as carefully as it should have been.

        I don't know about diagonals, since I haven't looked at anything
        round-bottomed.

        Since you are building Perigee, I assume you have the to-scale lines
        drawing. I suggest that you use the proper scale and check the table
        of offsets against the drawing. That is, after all, how the Atkins'
        got their tables of offsets. The lines drawing, not the table, is
        really the ultimate reference for the boat design.


        --- In AtkinBoats@yahoogroups.com, "Don Douglas" <douglashome@...>
        wrote:
        >
        > Happy Holidays to everyone!
        >
        > I have started lofting the lead keel section of Perigee. Currently
        I
        > have 1050 lbs of clean lead from tire weights (need 1400 lbs). So
        I
        > decided to make my mold for the keel. I plan on lofting the lower
        > center section around the lead keel and making mold patterns to
        strip
        > plank the form for the mold. This strip planked form will get
        faired
        > inside and re-inforced outside. I am only lofting sections 2-8
        from
        > the base to LWL. That omits 2 stem sections and 3 aft; 2 load
        lines
        > and the sheer. Tight on space until after Christmas.
        >
        > Here is my dileema. I know the table of offsets will need some
        > correcting and am ready for that. There were two points along the
        > bottom of the keel that were out by 3/8". The batten does not lie
        > and when drawn to the table of offsets, the line was very unfair.
        > The half-breadth plan for waterlines 1, 2, 3 are fair as are the
        > buttock lines 1 and 2 through this central section. So on to the
        > body plan. Waterlines and buttocks here match up nicely but if I
        try
        > to put in the diagonals...no luck, they are all out.
        >
        > I have rechecked my grid (fisrt time my waterlines were off by 1/4"
        > so out with the paint and a new canvas), verified all vertical and
        > horizontal measurements, verified the half-breadths and heights at
        > waterlines and buttocks, etc. All the diagonals are out by at
        least
        > 1/2" or more. If I refer to the lines drawing from the plans, I am
        > more confused. But I am not going to scale off from the lines to
        > verify anything. Would probably cause more errors and I don't have
        a
        > 5/8" = 1' scale nor can I find one.
        >
        > Has anyone had this type of problem with Atkin's Table of Offsets
        on
        > other plans? For me, I am rereading Chapelle and Vaitses, maybe I
        am
        > missing something.
        >
        > May warmer days be in your forecast
        > Don Douglas
        > Colorado Springs
        >
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