The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 24 – Hard Chine Plywood Construction 289
Figure 24-8 Applying adhesive mixture before bonding a
panel to the framework. <strong>The</strong> panel lying against the framework
in the foreground will be scarfed in place.
If you are using 3 ⁄8" (9mm) or thicker plywood, you can
scarf in place on the hull without worrying about
locating the joint over a solid member. In situations
where you find that your sheet is only a few inches
short of a frame and that you will have to cut off a
substantial amount of material to retreat to the previous
frame, the ability to scarf anywhere saves a great deal of
plywood. Marking is simplified because the scarf
doesn’t have to be centered on a fixed point. Make sure,
however, that there is enough longitudinal support
between the two panels to keep them reasonably
aligned as you scarf.
Figure 24-9 illustrates two methods for scarfing
between frames. <strong>The</strong> first, for thinner plywood, is to fit
and bond blocking between stringers with the centerline
of the blocking lined up with the centerline of the
joint. <strong>The</strong> second is to apply a temporary blocking. For
this, use plywood thick enough to receive a staple. Cut
it to the approximate width of the joint and saw it to
length to fit between the stringers. Someone on the
underside of the boat should hold the blocking in
position while another person staples through the scarf
from the top.
<strong>The</strong> only difficulty with this method is that you need to
support the interior blocking adequately so that it will
receive staples, but not push so hard that you force the
scarf joint up and out of fair during the assembly
process. With thicker plywood, this isn’t too difficult,
but it can be a problem with thinner material. You can
minimize this problem by securing the scarf joint with
staples at the stringers, keel, chine, or any other solid
area before applying pressure on the temporary
blocking. One advantage of using the permanent rather
than temporary blocking system is that this blocking
can serve as a core over which you can manufacture a
frame in the completed hull. In this case, frame material
is laminated on the interior blocking surface,
completing a rigid, I-beam type frame system, as
discussed in Chapter 22.
When you have installed all of the panels in one section
of the hull and the adhesive has cured, you can remove
all temporary staples. We always remove the staples
from the scarf joints and usually from the chine and
keel because of the heavy fairing that may take place in
these areas. <strong>The</strong> next step is to plane off the excess
plywood smooth with the opposite chine surface so that
you can fit and install the next panel on the other side
of the chine to create a plywood overlap.
Temporary blocking, made
from plywood scraps, goes
in with flat side against
the scarf. <strong>The</strong>re should
be plastic between
the blocking
and scarf.
Chine log
or clamp
Stringers
Permanent blocking
between stringers to support
the scarf. This arrangement lends
itself to I-beam frame construction.
Figure 24-9 Blocking between stringers for scarfing plywood
in place.