The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

284 Hull Construction Methods
Figure 24-2 Load-bearing bulkheads can be made from two
pieces of thinner plywood with a framework sandwiched in
between. <strong>The</strong> bulkhead arrangement shown above handles the
main beam loads from a trimaran’s outriggers.
<strong>The</strong> second difference is in the use of chine logs, longitudinal
members which act as stringers for structural
support at the chine joint and are critical for joining
panels. In hard chine plywood construction, chine logs
provide enough bonding area for holding the panels
together and protect potentially vulnerable areas of the
hull. Chine logs should produce joints that are potentially
stronger than the plywood.
As Figure 24-4 indicates, there are many successful
ways to make chine joints. <strong>The</strong> sharp edges which
Figure 24-3 In this set-up for a hard chine trimaran hull, the
builder has installed the chines and is fairing the frames.
Hardwood
cap
Epoxy
coated
end grain
Spruce or fir chine
Plywood planking
Chine log
Fiberglass tape
Fiberglass tape
over the radius
Plywood sides
Figure 24-4 Details of typical chine joints.
Spruce or fir
chine log
“Funky”
trimaran chine
Spruce or fir chine log
Heavy laminated
plywood bottom
usually result from these techniques do however
obstruct hydrodynamic flow, and this is a major disadvantage
of hard chine construction. Rounding sharp
edges minimizes the problem, but requires innovative
joining techniques which can provide large radii
without compromising joint strength.
Some designs, such as the International Fireball dinghy,
have two chines, each with flatter angles, on either side
of the hull. <strong>The</strong>se tend to expose a large amount of end
grain on the overlapping plywood. <strong>The</strong> usual procedure
was to avoid exposing end grain on the bottom of the
boat, so the bottoms were put on last and the end grain
exposed only on side surfaces. End grain well encapsulated
in WEST SYSTEM epoxy has proven very tough and
resistant to abrasion. Chines in this type of hull do,
however, receive more abuse than any other parts of the
hull, and it may be worth adding glass cloth to more
vulnerable joint areas to increase abrasion resistance if
hard usage is expected. Glass tape, available in 3" and
6" (76mm and 152mm) widths, can be applied to
chines and keels without a great deal of extra work.