The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

12 Fundamentals of Wood/Epoxy Composite Boatbuilding
Wood has many advantages as a boatbuilding material.
It’s probably easier, less expensive, and more satisfying
to build a boat from wood than from any other material.
Wood is relatively easy to cut and shape and almost
everyone has some experience with it. It’s satisfying to
work with because it’s beautiful. Wood is readily available
and it costs less than steel, aluminum, or fiberglass.
Although lumber prices have increased, wood is still
comparatively inexpensive in terms of both its own
cost and the cost of tools to work it. Most importantly,
however, wood has physical characteristics that make it
ideal for boatbuilding. Its strength, stiffness, light weight,
and resistance to fatigue give wood advantages over
other materials.
While wood has many advantages as a structural material,
it also has some well-known disadvantages, most
of which are caused by the passage of water in and out
of its cells. Wood can rot. It shrinks and swells with
changes in moisture and temperature, and it loses some
of its strength and stiffness when its moisture content
is high. In the past, difficulties arose in constructing
boats with wood because of changes in the condition
of the wood caused by variations in moisture content.
As its moisture level increases, the wood changes in
dimension and loses some of its strength and stiffness.
<strong>The</strong> design of boats built of wood had to make allowances
for this instability.
To a very great extent, the use of WEST SYSTEM Brand
epoxy overcomes the problems previously associated
with wood construction. All joints in boats built with
the methods described in this book are bonded with,
and all surfaces encapsulated in, epoxy. In this way,
every piece of wood, inside and out, is covered with a
barrier coating of WEST SYSTEM epoxy through which no
significant amount of water or air can pass. As a result,
the moisture content of the wood is stabilized.
This stabilization means that the wood will shrink and
swell very little. <strong>The</strong> moisture level at which the stabilization
occurs and at which the wood remains ensures
a continuation of design strength and stiffness. Encapsulation
in WEST SYSTEM epoxy also prevents dry rot,
not only by stabilizing moisture content, but also by
restricting oxygen supply to the wood surface.
Since World War II, there has been tremendous
research and development in the field of epoxy and
other thermosetting plastics. Wood research had focused
on technologies and products suited to the construction
industry. We are among the few to work specifically to
develop a wood/epoxy composite material and the only
group to test it exhaustively, especially in high-cycle
fatigue. Our efforts clearly show that a wood/WEST
SYSTEM epoxy composite is one of the best structural
materials currently available for building boats when
strength and stiffness-to-weight are primary considerations.
Because of the superiority of the composite in
fatigue, wood/epoxy hulls are less liable to failure over
time and after hard use than hulls built of other materials.
We will explain why this is so in this chapter
and discuss WEST SYSTEM epoxy in greater detail
in Chapter 4. See Appendix B for additional data on
wood’s mechanical properties.
Engineering for Wooden Boats
Boats present unique engineering problems. <strong>The</strong>y
require an outer skin, which may or may not be loadbearing,
but which must withstand and deflect tons
of water. Boats must also survive the kind of high
point loads that occur during launching and hauling
out, or if objects are struck at sea. Even small vessels
have tremendous amounts of vulnerable hull and deck
surface which must be properly supported to retain
their streamlined shapes. Large sailing rigs may cause
torsion and bending in hulls that have inadequate shear
bracing. Finally, boats must survive these loads continuously
over many years. <strong>The</strong> overall task in addressing
these problems is the successful integration of proper
design, construction methods, and material choices.
Boats demand a material that is strong and lightweight.
It must also be stiff, as demonstrated by the ability to
resist deformation under load. Within certain limits, the
lighter and stiffer a boat is, the better its potential for
performance and durability. <strong>The</strong> less a hull weighs, the
faster it will move under a given amount of power. <strong>The</strong>
stiffer a boat, the better it holds its true shape and resists
“softening” or weakening through flex and fatigue. Boatbuilding
materials must retain their strength and stiffness
over time and after use, and the boat’s structural components
and construction method must be designed to fully
exploit the materials’ capabilities.
<strong>The</strong>se principles may be best understood by thinking of
a boat hull as a box beam enclosed by hull planking,