The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

188 First Production Steps
will be to arrange these legs so that they don’t get in the
way of each other. You can cut out the centers of mold
frames to allow bracing to pass through them, but you
cannot hollow out bulkheads. Instead, plan to run
diagonal braces for bulkheads through companionways
and other cutouts.
Another point to consider in the set-up you are
putting a bulkhead in is whether it protrudes above
the sheer (such as one that might form the back of
a cabin above the deck line). If so, the set-up will
have to be high enough off the floor or strongback
to leave room for this.
Many other items that can be included in the set-up are
smaller than a bulkhead and will only span a portion
of the hull perimeter. In these cases, you cannot allow
these pieces to substitute for an entire mold frame,
though it may be possible to build partial mold frames
that can provide complete support in conjunction with
a partial frame member.
Other considerations that are necessary if you are going
to install permanent structures in the set-up will be
discussed later in the chapter. First, however, will come
a discussion of mold frame construction.
Mold Frames
Our favorite mold frame material is particleboard,
also known as chipboard or pressed wood board. It’s
inexpensive, dimensionally stable, and has no grain. A
4' � 8' (1200m � 2400m) sheet of 3 ⁄4" (18mm)
chipboard is readily available because it is widely used
as subflooring in residential construction, and a single
sheet is usually large enough to make both halves of a
mold frame.
Mold frames may also be made of 3 ⁄4" (18mm) lumber,
4" to 10" (100mm to 250mm) wide. If you use stock,
you will generally have to cut station line shapes out of
several pieces and then join them together with
plywood gussets.
<strong>The</strong> main job of any mold frame is to hold the shape
of the boat. So long as it is strong enough to do this, a
dummy frame may be open in the center, like a large
horseshoe, or closed, with material more or less solidly
arranged across the station. Once structural considerations
are met, the only difference between frame
designs is that it may be easier to attach legs to solid
frames than to open ones.
Transferring the Shape
Unless a designer specifies otherwise, you will need
to cut out mold frames for every station in the lofting.
<strong>The</strong> shape of the frame for each particular station is the
shape represented in the body plan of the lofting. Some
designers may specify extra mold frames in areas of
acute planking curve. <strong>The</strong>se are usually referred to as
half mold frames and are located midpoint between
stations.
<strong>The</strong> body plan shows only a half shape of each station,
so you will have to cut out each station shape twice and
then join the two halves together to form the full
station. However, cut only half of each mold frame by
the line transfer methods we are about to describe.
Cut out the other halves using the original halves as
patterns. <strong>The</strong> reason for this will be explained later
under the subject of controlling edges. Whichever
type of frame you use, remember to subtract planking
thickness from your lofted station lines before transferring
them to your mold stock. It may also be necessary
to subtract the thickness of mold planking. <strong>The</strong>se
deductions from your lofting may be substantial. To
build a 1 ⁄2" (12mm) thick hull on a mold with 3 ⁄4"
(18mm) thick ribbands, you will use half mold frames
that are 11 ⁄4" (30mm) “thinner” than your station
lines—so pay close attention to the planking thickness
deduction procedure outlined in Chapter 16.
<strong>The</strong> trickiest part of making mold frames is transferring
the station line shape from the lofting floor to the mold
frame material. As far as we know, there are four ways
of doing this. One method of transfer is to loft the body
plan on a portable board and then saw the board up
into templates. Naturally, this won’t work if the station
lines cross each other or even if they are very close
together. We can only recommend this method if you
loft the body plan twice, giving one lofting to cut up
and leaving one for reference.
A second method is to use tracing paper through which
you can see the lines. Spread the paper on the lofting
floor and trace the station lines either freehand or with
a batten. <strong>The</strong>n move the paper to the mold frame
material and make pick marks through it onto the