The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

260 Hull Construction Methods
ment. This method uses two opposing plywood pads
approximately 11 ⁄2" (38mm) square. Drill a hole approximately
the shank size of a number 8 screw on the pad
to be used on the outside of the first lamination, and
then drill a smaller pilot hole for a number 8 screw on
the pad for the inside. Put a number 8 sheet metal
screw with a washer through the outside pad through a
hole drilled in the gap between the two misaligned
edges of plywood to the inner pad, and screw both
pads up tight until the edges are aligned. (<strong>The</strong>re may or
may not be a gap present between the plywood edges
for misalignment to occur.) This is a foolproof solution,
but requires more time and energy than the staple
method, and we only use it when absolutely necessary.
With either method, use polyethylene sheet material or
wax paper between the plywood tabs and the edges to
prevent bonding between the two. However, even
without protection, it is not a particularly difficult job
to remove the plywood tabs with an offset chisel.
An attractive alternative to the staple and drill approach
in places where it does not take much force to align
panel edges is to hold the plywood scraps in place with
hot melt glue. Just apply a bead to hot melt to the scrap
plywood pad, press it in place at the same time making
sure the panel edges are aligned, wait a few seconds for
the hot melt to harden, and move to the next spot.
After the epoxy cures, a sharp chisel can be easily
forced between the plywood scraps and the hull
without damaging the hull. If you can get by with this
method, cleanup of epoxy squeezed out on the inside
of the hull is simplified greatly because the plywood
alignment pads are all applied to the outside of the hull.
Another factor affecting edge alignment is the width of
the plywood panel that is chosen. If a panel is too wide
for the amount of compound curve present in the hull,
the edges will tend to curl excessively between stringers.
This not only contributes to edge alignment problems,
but also can cause extra work when fairing up prior to
installing the second layer. <strong>The</strong> desire is always there to
use as wide a width as you can get away with so as to
save some labor in fitting time by reducing the number
of joints. However, with this method, it is better to be a
bit more conservative and use narrower panels than
you might choose for the mold or the strip plank
method. This might actually save time in the long run
by reducing the labor needed to align the edges and fair
the first lamination surface.
<strong>The</strong> first lamination of plywood is usually joined at the
centerline along the keel, but this is not necessary if it
would be advantageous—and the hull shape allows it—
to join in another area, such as at a bilge stringer. As
the panels run out at the transom, stem, and sheer
areas, allow a slight overlap of approximately 1"
(25mm) when trimming the ply so that you can
laminate subsequent layers slightly beyond the actual
hull. This will ensure good laminating pressure and a
lack of voids in the completed hull when the edges are
trimmed. Take extra care when bonding this first layer
to the stem, keel, and sheer. <strong>The</strong>se are the critical joints
in any boat: proper application of the first lamination to
these members is always important.
Cleanup
If you want to achieve a nice looking, natural interior
with the stringer-frame method of construction, proper
cleanup is extremely important and, unfortunately,
time-consuming. As plywood panels are installed over
the stringer-frame support system, you must clean up
the excess adhesive that exudes from the joints on the
interior before it fully cures. Again, we must emphasize
that the adhesive used should be thick enough so it will
not run down the stringers or the plywood skin as it
squeezes out from the joints because of the added
cleanup difficulties this causes. It is not necessary that
you remove the adhesive immediately; in fact, it is even
a little easier to remove after it has started to stiffen or
begun an initial cure. In this initial phase, the adhesive
gets considerably thicker, losing some of its ability to
adhere to other surfaces, and in this state it is easiest to
remove. If you allow the cure to go beyond this state,
removal of the adhesive becomes increasingly difficult
and is all but impossible when the epoxy reaches a
semi-rigid state. Depending on the temperature that
you are working in and the cure rates you are getting
with your epoxy mixture, you should plan your work
so that you clean up at given intervals during the
laminating process. If two or more people are applying
the plywood strips on the exterior surface, interior
cleanup can require the services of one person full time
to keep up.