The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

298 Hull Construction Methods
snugly. In some cases you can force wires to the left or
right as you twist them to assist in raising or lowering
one panel edge against the other. <strong>The</strong> goal of this final
tightening is to snug the plywood panels against each
other and to line them up so that there will be no
humps and hollows along the keel line.
Occasionally, wire ties may be mutilated to the point
where you lose control of the plywood edges around
them. <strong>The</strong> best solution to this problem is to snip these
wires, remove them, start over with fresh ties, and hope
for better luck. Drill more holes and insert extra wires
in areas that are particularly difficult. If you have further
trouble, it’s more than likely that you did not put enough
radius on your edges and/or that a hump or hollow on
a panel edge is throwing alignment out of kilter.
Constructing the Keel Joint
When the keel edges of the plywood panels are in
position and any wires tightened, begin the process of
building a keel joint. We recommend that you plan to
manufacture the keel in a single day as this will eliminate
sanding between layers.
<strong>The</strong> composite keel joint is one of the most critical
parts of a compounded plywood hull. Although the size
and composition of keel joints vary from hull to hull,
basic installation procedure is very similar. Begin by
filling the V formed by the two panels at the interior
keel line with a fillet of thickened epoxy, lay in fiberglass
cloth or tape, and apply more epoxy and fiberglass
cloth. <strong>The</strong> epoxy structurally joins the panels and, at
the same time, serves as a core between the inner and
outer layers of fiberglass.
<strong>The</strong>re are no firm rules for the thickness and width of
composite keels, but the fillet should at least cover
protruding wires if you are using them so that you can
evenly apply the glass over a smooth surface. <strong>The</strong> size
of a keel joint, and especially its width, has a significant
effect on the shape of the finished hull, and it is a
rather rigid part of the structure, which for the most
part will not bend. If it is irregular, larger in some areas
than in others, it may cause bumps and hollows.
Variation of around 10% in the keel section is tolerable,
but any more than this will lead to unfairness in the
hull. (See Figure 25-9.)
Thickened epoxy
keel fillet. Make the
fillet large enough to
cover any exposed tie wires
and keep the fillet fair and
even from end to end.
Wet out fiberglass tape and
carefully position it on the keel.
Keep epoxy and tape evenly
spaced on each side
of the keel
centerline.
Figure 25-9 Building a composite keel joint.
Circular plywood
paddle for shaping
the keel fillet
Extending fiberglass
tape farther from
the centerline will
add fullness to the
underbody by stiffening
the plywood
panels.
Keep epoxy
off area outside
of the fiberglass tape
as epoxy will stiffen the
plywood and can cause unfair
spots in the folded hull.
To apply the initial keel joint fillet, add low-density
filler to epoxy to make a mixture that spreads easily but
resists sagging. Apply it as smoothly and evenly as
possible. <strong>The</strong> scribed lines on the interior of the panels
aid in maintaining a balanced fillet as well as in laying
the tape straight. Since leaning over the edges of the
spread-out panels to reach the middle of the hull can
be a bit difficult, we make several paddles, each resembling
the keel shapes we want at a given part of the
hull, and use them to remove any excess adhesive and
to smooth the joint.
Apply fiberglass cloth tape over the fillet when the
thickened epoxy mixture has partially cured. If you
wait until the epoxy has fully cured, you will have to
sand before applying fiberglass. Catching the fillet while
it is still pliable and malleable means that you can
simply smooth potential rough edges with layers of
glass cloth.
In manufactured keels, we usually use 9 oz (305g/m2 )
fiberglass cloth tape. This is available in various widths;
we keep a supply of 2", 3", 4", and 5" (50mm, 75mm,
100mm, and 125mm) rolls on hand for building
various sizes of keels. We typically install two layers of
tape on both the inner and outer keel surfaces of hulls
built with 5 ⁄32" to 1 ⁄4" (4mm to 6mm) plywood. Like the