The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 19 – Keels, Stems, and Sheer Clamps 209
therefore are usually more desirable, but they usually
have to get thicker to get wider. When trying to develop
sufficient bonding area at various station positions, you
will find that the flatter areas in the middle of the hull
permit the use of a thinner keel section, while the finer
bow area will require a much thicker keel section to
provide the same bonding area. Stems may have to be
two or three times thicker than keels because the sharpness
with which the planking joins the hull at the stem
limits bondable area.
When you have developed the keel shape at a few
stations, you can loft and fair the keel at all of the
stations on the lofting board. It is important to
remember that you need to subtract the cap thickness
from the outside lofted profile of the hull in order to
define the keel and stem profile. <strong>The</strong> stem is sometimes
difficult to project properly in the lofting. See Chapter
16 for a detailed discussion of this procedure. Chapter
16 also gives instructions for the development of all
stem dimensions.
Also lay out the area, usually near the forefoot, where
the keel and stem meet. A 10- or 12-to-1 scarf bevel is
needed for adequate strength, so the joint may be quite
long. Because its two parts may curve slightly, a
keel/stem scarf joint can be difficult to manufacture.
<strong>The</strong>re are no hard and fast rules about the direction—
stem over keel or keel over stem—the scarf should run.
After lofting the stem and keel, locate the scarf. <strong>The</strong>n
draw in the bearding line, which shows the inside
intersection of the planking and the stem or keel. Make
a pattern or template of the area where the stem and
forward end of the keel join. <strong>The</strong> easiest way to do this
is to use the nail method of transferring lines described
in Chapter 17. It’s best to pick up all pertinent profile,
sheer, scarf, station, and bearding lines at the same
time. Check all measurements and label all lines clearly.
Cut out the template and carefully trim it to the profile
shape on the lofting.
If you are planning to build your boat using the mold
method for laminating hulls, the process of installing
a permanent stem in your mold may involve a few
extra steps. An inner mold stem may be necessary. Loft
and shape this piece before you begin work on your
keel/stem unit, following instructions in Chapter 20.
Figure 19-2 <strong>The</strong> laminated stem for the proa Slingshot. <strong>The</strong>
extra blocking on the side of the stem is for the slight flare in
the bow. Note the set-up cable on the floor and the notch for
the cable in the stem at the lower left corner of the photo.
At this point, you should have a reasonably clear idea of
the shape and dimensions of the keel and stem, so you
can prepare stock to laminate the blank for the stem
and keel. You can laminate the stock to the exact thickness
desired, but you should always add a little extra
width to allow for trimming after the blank is
completed. While it is possible to save some stock by
varying the lengths, widths, and thicknesses of the
stock in the laminate, this is normally more complicated
than it’s worth because of the great amount of
planning and work involved in cutting out and properly
lining up all of the different size pieces. It’s more
practical to control the thickness of a keel or stem by
step tapering the wood along the length.
Make the keel and stem blanks a little longer than you
will actually need them. <strong>The</strong> scarf joint will use up some
of this surplus so plan for it. Since the forward tip of
the stem blank is usually fastened securely to the floor
or strongback in the set-up, extra stock beyond the sheer
line may be necessary. <strong>The</strong> keel blank should extend a
short distance beyond the transom to facilitate fairing.
Springback may complicate construction of both the
keel and the stem, and it can make proper alignment
difficult. In keels, springback can sometimes be so
slight that you can push the piece back into position.