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Re: Small Sailboat Design Help Request (or Designed for Plywood)

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  • Bob Johnson
    Boats that are designed for plywood construction have surfaces that are designed as sections of cones, cylinders, or planes. These are the geometric shapes
    Message 1 of 1 , Oct 9, 2010
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      Boats that are designed for plywood construction have surfaces that are
      designed as sections of cones, cylinders, or planes. These are the
      geometric shapes that a sheet material can easily be wrapped around,
      bending in only one direction without twist. A design for traditional
      planked construction, even though it may have flat looking sides, may
      have considerable twist or change in angle from the transom to midships
      to the stem. Plywood does not twist readily. Some designs for planked
      construction may very well be built in plywood, with no twist or maybe
      just a little needed to get the ply to conform to the shape. Others
      may simply not be able to have a single piece sheet side bent and
      twisted to the needed shape. These are prime candidates for glued
      lapstrake construction using plywood planks.

      To try and see how suitable a given design might be for sheet plywood
      construction, look a whether or not the lines of the various sections
      remain parallel. A flat bottom almost always is and therefor can
      utilise sheet plywood. The sides may or may not. If they are parallel
      from stem to stern, then that indicates that the side is a section of a
      cylinder and can also easily be planked from sheet ply. If they are
      mostly parallel but not quite, then they may possibly be able to use
      sheet ply with just a little torturing at the ends. The easiest way
      to check is to build a model from card stock and see how much twisting
      is needed to make a flat sheet fit the shape of the side, but be
      careful because cardboard is much easier to twist than plywood.

      "Tortured" plywood construction was in vogue for a while in the
      popularization of the plywood/epoxy technique, where the ply was bent
      and twisted in multiple directions, but the results were not completely
      predictable from boat to boat as each sheet of plywood might take a
      slightly different curve. Strip or glued lap are much more suitable
      for complex shapes.

      Bob
      ---

      On Saturday, October 9, 2010, at 02:03 PM, AtkinBoats@yahoogroups.com
      wrote:

      > 1a. Re: Small Sailboat Design Help Request
      > Posted by: "r_mouradian" r_mouradian@... r_mouradian
      > Date: Wed Sep 29, 2010 9:17 am ((PDT))
      >
      >
      > I'm wondering if anyone can comment on what it means when one of the
      > Atkins designs is noted as being drawn for plywood construction.
      >
      > I have notcied that many of the Atkins skiff-like designs appear to
      > have flat, or non curved, sides when viewing the frames. But, only a
      > few are recommended for plywood. For example, Sunshine and Krazy Kat
      > look to be almost identical, but I am guessing that the actual
      > 3-dimensional shapes are slightly different and that Krazy Kat would
      > be harder to build in plywood?
      >
      > Regards
      >
      > Rob
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