The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

266 Hull Construction Methods
Strip composite construction is another variation of
strip planking. Strips are joined as with the previous
variations, but all cross-grain reinforcing is done with a
layer, or layers, of fabric, bonded with epoxy on the
inside and outside. This results in a stiff, strong, often
frameless, lightweight structure. With single layers of
fabric, the epoxy and fiberglass cure clear, allowing the
wood’s natural beauty to show. Popular examples of
strip composite construction are stripper canoes. <strong>The</strong>y
are usually built of 1 ⁄4" (6mm) thick cedar strips,
planked over temporary frames, with 4 oz (135g/m2 ) or
6 oz (200g/m2 ) woven glass fabric inside and out.
Though used most often for smaller boats, strip
composite construction is not limited to small craft or
to standard boat shapes. Larger custom racing craft may
be constructed this way. For example, the Formula 40
trimaran Adrenalin used unidirectional carbon fiber
reinforcing laid at 90° to the 3 ⁄8" (9mm) thick cedar
strips.
<strong>The</strong>re are many variations of reinforcing materials and
many choices of strip composites. When higher density
materials such as mahogany, cedar, and pine are joined,
they contribute to the structure and are considered an
“active core.” <strong>The</strong>y provide tensile and compressive
strength along the grain, as well as shear strength
through their thickness. Such a core may require
minimal reinforcement, depending on grain strength
and how the composite will be used. In contrast, a
lower-density core (such as foam strips) provides shear
strength but does not add longitudinal strength or
significant compressive strength.
Setting Up for Strip Planking
With strip plank construction, just as with the mold
method, we use 5 ⁄8" (15mm) particleboard as temporary
mold frames to define the shape of the hull. Set up the
frames as described for the mold method and then
cover them with strip planking. <strong>The</strong> only difference is
that extra care must be taken to be sure that the bevels
on the frames are correct. Hard spots may dent the
planking as it is bent over the frames, and this damage
can be visible in the interior.
Decide temporary mold frame positioning and spacing
during lofting, taking into account the locations of
stationary bulkheads, framework, and any other
internal items which might interfere with a chosen
temporary frame location. Usually, setting up a permanent
bulkhead means that you can eliminate a
temporary frame, but sometimes a bulkhead is situated
between two temporary frames and too large a gap
would be left if either were removed. <strong>The</strong>refore, early
on, coordinate the locations of the permanent structural
members which can act as mold frames with the
locations of the temporary mold frames so that you can
provide proper support for the strip planking process
with the least amount of set-up.
Planking thickness and the shape of the hull determine
the standard spacing between mold stations. For 1 ⁄2"
(12mm) thick planking, a 16" (400mm) span between
stations is about maximum. Frames that will be covered
with 1" (25mm) thick planking might be as far as 30"
(760mm) apart. Average spacing for 5 ⁄8" to 7 ⁄8" (15mm to
22mm) planking is 18" to 24" (460mm to 600mm).
With any hull, there may be areas of tight, sharp curves
which cannot be properly defined by the general station
spacing. We usually insert half frames between two
normally positioned frames in these areas. If there aren’t
too many sharp curves, this is much quicker than
decreasing the standard frame spacing throughout the
hull to accommodate one area of sharp curves.
With strip plank construction, the keel, stem, and
transom are always included in the set-up to become
part of the permanent hull. This means that you will
have to make provisions for notching the keel and stem
into the temporary mold frames as well as into
bulkheads and laminated frames which may also be in
the set-up. Hold the keel and stem temporarily in place
to each temporary mold frame by inserting a screw
through a small block that is attached to the side of the
temporary mold frame just underneath the keel or stem
area. <strong>The</strong> screw holds the keel or stem snug against the
temporary mold frame until the lamination process is
complete. You can then remove these screws easily
when it is time to remove the temporary mold frames.
Permanently position and attach the keel and stem to
bulkheads, frames, or any other permanent interior
items, using epoxy held in place with alloy wood
screws of proper length.
A permanent or temporary sheer clamp must be
included in the set-up so that the planks near the sheer
can attach to it, especially if the planking will run out