The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 25 – Compounded Plywood Construction 303
Figure 25-18 Bonding resin-coated paper honeycomb panels
to the inside of a folded plywood hull. Sticks are providing
clamping pressure by forcing the honeycomb against both sides
of the hull. When this laminate has cured, 12 oz fiberglass
cloth was bonded to the interior side of the honeycomb core.
the addition of glass cloth will increase the weight of
the hull significantly, chances are you will find that the
hull skin is incredibly light, at this point probably not
comprising any more than 50% of the completed
weight of your hull. Thus, you may well be able to
afford the extra weight.
<strong>The</strong> main benefit of using glass cloth to stiffen the
plywood hull panels is that it applies easily and quickly
with effective results. Applying glass cloth on both the
inner and outer hull surfaces is especially effective with
3-ply plywood because it produces a 5-ply matrix after
the plywood skins have been formed, increasing strength
and stiffness significantly. When using glass, apply it
only to the interior of the hull at this stage, leaving the
outside to be glassed after the interior is completed and
the hull can be removed from the deck jig and turned
upside down. With the hull in that position, the outside
layer of glass cloth is much easier to apply.
Another method to stiffen all or part of a plywood skin
is to treat the developed hull as a mold and use it as a
form over which to laminate veneers or more plywood.
You can do this either on the inside or outside of the
hull skin, but it is probably more easily and effectively
done on the outside if the whole hull is to be covered.
Another interesting method that we have used is to
laminate a honeycomb material on the inside of the
compounded plywood hull, using a thickened epoxy
mixture for bonding. We then cover the honeycomb
with a layer of 12 oz (410g/m2 ) glass cloth to complete
a sandwich panel which has a high degree of panel stiffness
at a very light weight. <strong>The</strong> only difficulty with this
approach is determining how best to distribute high
load points over the interior of the hull skin with the
honeycomb in place. In the case of the trimaran outer
hulls shown in Figure 25-18, there were very few high
load points involved, so they were a natural for this
type of skin support. <strong>The</strong> beauty of the system in this
instance is that the honeycomb and the 12 oz glass
cloth were easily installed on the interior with few labor
hours and resulted in a skin that needed no further
support.
Before installing any framework or doing any stiffening
of the skin, make sure you are satisfied with the exact
shape that the hull has taken. If not, you can easily
make some modification of the shape at this point. For
example, you can squeeze the hull in at various points
or push it out at other points with temporary braces or
supports. <strong>The</strong> interior structure that you then build in
must be capable of holding these altered hull shape
positions without losing any hull fairness after you
remove the supports. At this point, you’re down to
“eyeball” boatbuilding because you have no body plan
or given set of dimensions to go from. If you are
building a hull you designed yourself, there are several
parameters that you can establish early in the game as
goals to shoot for in developing a given hull shape.
<strong>The</strong>se will be discussed later. If you are building from
plans (for example, a Tornado catamaran), there is
usually no guide to determine final hull shape other
than the initial instructions for construction.
Interestingly enough, however, the variation between
hulls built by different builders (as shown by the class
measuring templates) is surprisingly small in the
Olympic class Tornado.