The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

192 First Production Steps
image and a mirror image with any of the line transfer
methods. <strong>The</strong>refore it is necessary to use the original
half-mold as a pattern for the other half in order to get
the control sides on the same sides when you truss the
halves together.
Once the second halves are cut out, mark them for
control sides and number them. Check them against
the lofting or the original halves for accuracy and
numbering.
Assembling the Mold Frames
<strong>The</strong> two halves of a mold frame are held together with
a plywood gusset in the area of the keel and with a
spall. A spall usually spans the mold frame at the
highest waterline of the station. We find that it’s most
efficient to prepare these pieces in advance and bond
and mark as many as possible in a single operation on
the lofting floor.
You can make the gusset out of 1 ⁄4" or 3 ⁄8" (6mm or
9mm) plywood. Cut it out in the approximate shape
of the lower 12" (300mm) of the station. <strong>The</strong> gussets
should be of generous size so that they give plenty of
support. It is best not to place them up to the edge of
the mold frame, but to keep them an inch away from
the edges. You will eventually bevel the edges, and
there is no good reason to include the gussets in the
beveling operation.
Spalls are usually made of either 1" � 4" or 1" � 6"
(19mm � 89mm or 19mm � 140mm) boards, well
seasoned so that they will not shrink or swell at some
point after installation. Every spall must have one long,
straight edge, for in addition to functioning as bracing
members, spalls are applied so that one edge serves as a
set-up reference line. Although it makes no difference
in many cases, it’s usually better to place a spall with its
straight edge facing up in the set-up. This way, you can
set a level on top of it for reference and better see the
edge when you measure. Keep the ends of a spall in 1"
or 1 ⁄2" (25mm or 12mm) from the edges of the mold
frame so they do not interfere with the fairing of bevels.
<strong>The</strong> greater the distance a spall must span, the greater
the chances of its becoming unstable. Instability will
destroy its usefulness as a reference line. If the boat
you are building has a great deal of beam, you should
Figure 17-4 Fitting and assembling frames for a double chine
trimaran hull on lofted sections.
probably support the spall toward the center with
trusses running at an angle to the mold frame. An
alternative is to position the spall slightly away from
the reference waterline and to stretch a string across
the waterline marks. You can then use the string for
reference during setting up.
To truss the two halves of the mold frame together,
place the frames control side down on the lofting floor.
Only one half will fit into the body plan lofting. <strong>The</strong>
other half, being a mirror image, goes on the other side
of the lofting centerline. To locate this half in symmetry,
you have to measure the offset of the highest waterline
(the distance from the centerline to the body plan line)
and transfer it out in the opposite direction.
Make a tick mark or drive in a small nail and locate the
mirror half out to this mark. Also butt the two halves at
the keel.
<strong>The</strong>n apply the gusset to the non-control side of the
mold frames. Bond the gusset in place with thickened
epoxy, using screws, nails or staples as fasteners.
Recheck the position of the two halves, and then you
are ready to apply the spall. Before the spall goes on,
however, you must draw a line against which to align
the straight edge of the spall. Use two small squares
and place their edges sitting vertically on the waterline
on the lofting floor. <strong>The</strong>n use the spall itself as a
straightedge and push it gently against the two squares.
When it is in position, draw against the spall’s edge,
across the face of the mold frames. Use this line to
reposition the spall when you permanently install it
with adhesive and fasteners.