The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 25 – Compounded Plywood Construction 307
Figure 25-27 Construction on outriggers for a 35' trimaran.
<strong>The</strong>se hulls will now be coated and fiberglassed. See Chapters
13 and 15.
Figure 25-28 A Tornado catamaran folded up and inserted
into the deck jig. <strong>The</strong> exterior keel has been faired and taped
with fiberglass.
out the surface first with a light coating of epoxy. Apply
the glass tape dry, firmly setting it in position in the
epoxy. <strong>The</strong>n wet out the glass tape by adding more
epoxy, either with a roller or by pouring it on the
surface from a cup and smoothing it out with a plastic
squeegee. We usually wait for the keel line taping to
cure completely and then file or sand the glass tape
edges as smooth as possible. We then attempt to fair
them with putty, using low-density filler. If the exterior
surface is to be covered with a layer of glass cloth, we
wait to do this puttying operation until after we have
applied the fiberglass cloth. Other areas of the hull may
also need fairing. <strong>The</strong>se could include the scarf joints
and any hollows that may have developed.
<strong>The</strong> final stage of hull completion is the fairing of the
deck beams and installation of other deck structural
items such as longitudinal stringers. (See Chapter 27.)
Design Guidelines for Model Building
<strong>The</strong> process of designing compounded plywood hulls is
not very scientific. In fact, it’s probably more a combination
of art and common sense than anything else.
Because the compounded plywood method promotes
graceful shapes, we haven’t seen any really bad hulls
built using it, but that’s about the only encouraging
word we can offer.
<strong>The</strong> limitations of the compounded plywood system
demand high length-to-beam ratios—20-to-1 is not
uncommon—and high prismatic coefficients with no
sharp curves. <strong>The</strong>se factors add up to hulls that drive
easily through the water. <strong>The</strong> real design problems lie in
achieving enough displacement for a given hull length,
reducing the wetted surface to an acceptable minimum,
and arranging displacement throughout the hull for a
sea-kindly and maneuverable boat which sits correctly
on its lines when fully loaded. With compounded
plywood construction, you can’t always build what you
draw, so including all of these design considerations in
drawings is particularly complicated.
For centuries, model building has been an alternative to
designing boats on paper. Nathaniel Herreshoff refined
the technique, carefully shaping, testing, and reshaping
models until he was satisfied with a design and then
taking the lines off the models for lofting. We use models
for developing compounded plywood hulls because at
this point in the development of the boatbuilding
method, it appears to be the only practical way to
achieve accuracy.
By designing and building models on a scale of 1" to
the foot ( 1 ⁄12th scale), we have been able to project our
results accurately from the model phase up to full size
with very little error. We have built many models of a
given design, slightly changing various parameters of
each model hull until we finally achieved exactly what
we wanted. We then transferred the dimensions of the
model to paper and expanded it up to where we could
construct the full size version easily. Because of the