The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

302 Hull Construction Methods
Figure 25-15 Taping a keel fillet with the hull in temporary
frame supports (left). A folded hull with a deck jig in place
over the sheer (right).
Although strapping is better in most applications,
especially with larger hulls and masts, you can also use
light line to pull a hull into shape. Fasten screws into
both sheers every 2' or so down the hull, setting the
heads out far enough so you can wrap the line around
them. Thread a drawstring around two screws, one on
either sheer, and tie it with a rolling hitch. Tighten the
stringers up and down the hull by pulling on the knots
with steady and progressive pressure.
Supporting the Compounded Plywood Skin
Every hull needs some form of minimal framework to
distribute high load points over the hull skin, and the
framework systems that we have used to accomplish
load distribution have varied widely. Smaller boats,
such as the 18' (5.5m) Unicorn catamaran, rely on only
three bulkheads and several stringers to distribute loads
out over the 5 ⁄32" (4mm) plywood skin, sufficient
reinforcement for a long-lasting hull. As boats get
larger, however, they need more support for the skin
because the loads are increasing dramatically while the
plywood thickness may only increase a small amount,
for example, from 3 ⁄16" to 1 ⁄4" (5mm to 6mm).
Another factor that affects the amount of framework
needed for skin support is the stiffness of the skins
themselves. If you improve the stiffness of the skin, less
framework is needed. Coating the ply panels inside and
out with WEST SYSTEM epoxy will improve skin stiffness
a great deal. A step beyond this is to laminate 4 oz to
12 oz (135g/m2-410g/m2 ) glass cloth on both the inside
and outside of the developed plywood hull. Although
Figure 25-16 A folded 30' hull with sub-level stringers
laminated on the inside.
Figure 25-17 Struts and bracing for sub-level stringers in
a Tornado catamaran hull. Note the small plywood gussets
holding the struts to the stringers. Small plywood half frames
are being installed against the hull skin. <strong>The</strong>se frames will
be filleted to the skin. <strong>The</strong> centerboard case is the vertical
structure in the middle of the hull.