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