The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

278 Hull Construction Methods
Saw cut through
one belt & core only
Conveyor belting
or vinyl skins
Foam core
Figure 23-18 Custom sanding blocks can be made by
bonding flexible belting material to a wood or foam core.
Vary the core thickness and the saw cut spacing to adjust
the flexibility for various curved surfaces.
the same day. This may take two to three coats of epoxy
to accomplish. <strong>The</strong> fill coats can be applied as soon as
the previous coat of epoxy has cured to a firm tacky
state. This level of cure can take from one to four hours
depending on the temperature in your shop. After the
epoxy has cured, sand initially with 80-grit paper and
then with 120-grit paper until the surface is smooth
and dull. If you’ve sanded into the fiberglass weave,
apply additional coats of epoxy to seal these areas
before sanding again.
At this point, build a cradle. Unbolt the mold frames
and turn them sideways to free the canoe. Turn the
boat over and place it in its cradle. Sand the interior
with a disc sander and soft foam pad as well as with a
block where necessary. <strong>The</strong> flexible sanding block
shown in Figure 23-18 works well.
Apply fiberglass on the inside exactly as you did the
outside, with one overall layer and a second layer in the
flat bottom section. Ideally the inside of the canoe
should be glassed as soon as practical so that the
moisture content of the planking does not have time to
change. Increasing moisture content will lead to oilcanning
(loss of hull shape due to swelling wood
fibers). A 4%-6% change in moisture content on a thin
planked hull glassed on one side only could be disastrous.
Lay out the sheer clamp and trim it to shape. Laminate
gunwales and breasthooks. Double check the width of
the hull and install thwarts. <strong>The</strong>se are usually hung
from screws, which fasten up into the gunwales. Build
or buy seats to your liking, install them, and finish the
canoe as you would a strip plank hull.
Strip Composite Components
Strip composite construction methods can be used to
build many boat parts. One of the more interesting
applications is in building spars up to about 30' (9m)
long. <strong>The</strong> same technique may be used to build cabin
tops and other panels and components where design
considerations favor low weight and minimal interior
framing, or where heavy compound curvature
precludes the use of plywood.
In the past, solid masts were built by shaping a rectangular
piece of wood into an airfoil and then, if weight
was a problem, hollowing out the center. We suggest
that instead of building spars this way, you begin with a
male form which describes the shape of one half of the
mast, strip plank it, sheath it with glass, make a second
half, and then bond the two together. <strong>The</strong> resulting
spar is lightweight and can be designed to receive
specific loads. Because this type of construction has not
been widely used, we cannot recommend strip dimensions
and fiberglass schedules. Smaller spars will
probably require both high-density wood strips and
softwood. It is possible to taper the wall thickness and
section of a freestanding mast, but as with all other
aspects of strip composite spars, careful study must be
made to correctly address anticipated loading.