The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

282 Hull Construction Methods
and after construction, encapsulating the wood to stabilize
its moisture content and to protect it from the
harmful effects of moisture. We can produce very light,
stiff, strong, and long-lived hulls by using the bonding
and sealing qualities of WEST SYSTEM epoxy in combination
with good plywood and lumber.
Best of all, sheet plywood is probably the easiest and
fastest material to work with when building a hard chine
hull. <strong>The</strong>re are a number of reasons for this. For instance,
the lofting of a hard chine boat is greatly simplified
because most of its surface area is in a one-dimensional
plane. When lofting a hull that has compound curvature,
you must define all points on its surface; with a
hard chine hull, you only need to define the location of
the chine, keel, and sheer points on the lofting board.
This simplifies and greatly speeds up the lofting process
and enables you to develop a body plan in a fraction of
the time normally required for a typical rounded-hull
shape. In addition, the time needed to mark, cut, and
assemble mold frames or permanent frames is greatly
reduced because the process is much easier.
Frame Assembly
In other boatbuilding methods, mold frames are removed
when the hull is finished. In hard chine construction,
however, most frames stay permanently in the boat
because the flat planes of plywood hulls usually require
the support of substantial framework for adequate stiffness.
Although frames can be made of plywood, the
straight sections of hard chine hulls often make straight
stock a better choice structurally and economically.
Usually, we decide early in the project on a standard
size of frame material—1" � 3" (19mm � 63mm)
stock is typical. Two main factors that determine the
size of the frame material are the weight and size of the
boat, and the dimensions of the stringers and chines
that will be notched into the frames. A notched frame
must retain adequate load-bearing capacity. For example,
if you are going to set 11 ⁄2" � 3 ⁄4" (36mm � 18mm)
stringers on edge into 3" � 3 ⁄4" (75mm � 18mm) frames,
you can only count on 11 ⁄2" of the frame material to be
load-bearing until the outer skin is applied. You will
have to decide whether the 11 ⁄2" of unnotched frame
stock is adequate for your particular situation.
After you have decided on a standard dimension for the
frame material, prepare enough of the desired stock to
make all of the frames in the boat. In many cases, you
can save time by rounding over (or “radiusing”) what
will be the interior edge and then sanding and
precoating all of the frame stock before it is sawn and
assembled into frames. In some cases, however, it may
be easier to perform these finishing operations after you
have assembled the frames.
All the frame joints which will meet either at a chine or
keel must be at least as strong as the timber stock that
is being joined. A joint system that we have used with
great success consists simply of butt fitting the two
pieces of timber together and then covering each side of
the frame with a gusset of plywood. Orient the grain of
the gusset so that each ply crosses the joint at a 45°
angle, thus giving maximum strength. For accuracy, this
assembly is best done in a two-step operation. First, cut
the frame stock to proper size and take care to fit the
individual pieces of the frame together, using nicely
fitted butt joints as the only contact between the
individual pieces.
To ensure accuracy, temporarily position the pieces on a
developed full size body plan from the lofting floor or a
full size frame pattern that has been transferred to
either paper or Mylar. Use the full size lines as guides
to lay out the frames. When you have fitted all of the
individual joints to your satisfaction, insert wax paper
or a thin polyethylene sheet under the edges to be
joined to prevent any bonding with the surface on
which the fitted frame stock is resting. Coat the butting
edges of the frame pieces with adhesive and reassemble
them on the body plan surface. Hold the frame pieces
in perfect position using small nails (around the
perimeter) or weights until the adhesive cures.
Frame
joint at
chine
Sheer clamps or battens
Stringers
Blocking for gusset,
if necessary
Plywood gussets
on both sides of
the frame
Bottom
frames Keel Limber holes
Figure 24-1 Typical frame assembly showing gussets, filler
blocking, and the position of structural members.
Side
frames