The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

36 Fundamentals of Wood/Epoxy Composite Boatbuilding
these various loads. Typically, this meant placing longitudinal
planking on lateral ribs or frames. In a laminated
hull, by contrast, wood fibers run in all directions. No
single piece of veneer must take an entire load in cross
grain; instead, different layers share it. Because the
laminated hull is better designed to receive stress, it
requires less framing support than a traditional boat.
Laminating thus allows use of unidirectional material
to build an isotropic monocoque. Unanticipated loading
is far less threatening when a structure has strength in
every direction. Wood is lighter than other materials, so
a wooden hull can be thicker, for the same weight, than
a hull built of other isotropic materials.
Hot and Cold Molding—
A Historical Perspective
Laminating techniques depend on adhesives. Over
the years, methods and technologies used to laminate
boat hulls have, at least in part, developed around the
specific requirements of glues. Different adhesives
require different amounts of clamping pressure and
different cure temperatures. Some require tight fits,
while others can span voids. <strong>The</strong>se factors in particular
have determined the history of laminated hulls.
Early laminated hulls were made by hot molding, the
process by which most plywood is made today. This
technology developed rapidly during World War II
when steel was in short supply. Adhesives then available
required heat—often in excess of 300°F (149°C),
hence the name hot molding—and, frequently, 75 psi
of pressure to bond properly. Laminating was complicated
because large autoclaves were needed to provide
these temperatures and pressures. Capital investment
for pressure vessels and molds was very high, so hot
molding remained strictly within the economic range
of “big business.”
For 10 to 15 years after the end of World War II, some
leftover hot molding equipment was used in production
runs of various sizes and types of boat hulls. Luders 16
and Thistle class sailboats and small Wolverine outboardpowered
runabouts are examples of hot molded
laminated hulls. Just as the autoclaves and tooling
were wearing out, the fiberglass boat industry came
into its own with lower production costs and a more
marketable, seemingly lower-maintenance product.
Hot molded hulls couldn’t compete against this combination,
and soon the industry died out.
In the early 1950s, adhesives that required neither heat
nor pressure came onto the market. Hot molding
gradually gave way to cold molding. Cures could be
reached at room temperature with contact pressure, so
the expense of pressure vessels was eliminated. A
simple mold or form and staples were all that were
needed to hold laminated parts together as they cured.
Since a minimum number of tools and little capital
were necessary, small builders could practice the
laminating procedures that had been limited to large
enterprises.
While our hulls may be considered cold molded, we
prefer to think of them as laminated. Our methods are
a direct outgrowth of hot molding technology as it was
applied to both boats and aircraft during the World War
II period. WEST SYSTEM ® Brand epoxy, our contribution
to this string of developments, has no special
clamping or temperature requirements. Its gap-filling
capabilities are an advantage when clamping pressure
is limited, and, with this epoxy, careful fits are not of
paramount importance. Our wood/epoxy laminating
techniques can produce far better results and longerlived,
lower-maintenance boats than were previously
possible.
At the <strong>Gougeon</strong> <strong>Brothers</strong>’ shop, we have used three
basic wood/epoxy composite hull laminating methods:
the mold method, the strip plank method, and the
stringer-frame method. <strong>The</strong> mold required for each
method varies in complexity and, within each method,
endless variations provide flexibility in different situations.
Each method has advantages and disadvantages,
which are discussed briefly here. More detailed instructions
on each hull laminating technique follow in later
chapters.
<strong>The</strong> Mold Method
<strong>The</strong> mold method for laminated veneer hulls was
popular in the early years of wood/epoxy composites
but is used infrequently now. It is most broadly used
now in building custom, one-off racing boats using
advanced composite materials. A mold or plug is a
form over which to laminate veneer or plywood to the
desired hull shape. It provides a solid base on which to