The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 19 – Keels, Stems, and Sheer Clamps 215
Shock loads from grounding and resultant
force on keel cause tension break in keelson
Grounding force
Figure 19-9 <strong>The</strong> effect of grounding on the keelson. Shock
loads from grounding and the resultant forces on the keel cause
a tension break in the keelson at the back edge of the keel.
keelson is relatively easy to repair by simply scarfing in
another piece in the area that has been fractured, and
the repair costs little in materials or labor hours. This is
a great savings when compared to the possible damage
that the hull itself might sustain without this arrangement.
(In two instances, large IOR boats that we have
built have had major groundings on rocks. In both
cases, the keelson concept worked beautifully, absorbing
most of the energy that was generated by the tremendous
grounding forces.)
Another structural advantage is that you can make the
lower keel itself much smaller than normal, permitting
laminated floors or ribs of the maximum size to pass
across the keel with the minimum amount of notching.
This provides excellent athwartship load distribution
and provides maximum usable headroom space in the
process. <strong>The</strong> keelson represents a very efficient use of
material and takes relatively few hours to manufacture.
Centerboard and Daggerboard Cases
Centerboard and daggerboard cases are, in effect, extensions
of the keel that provide a cutout for either a
centerboard or daggerboard to pass through. <strong>The</strong>y are
also points of extreme high loading, and it is very
common for damage and leaking to occur in these areas
of the boat. Because of this, you should carefully build
up the keel in the area in which you install a case. To
do this, you might make the keel much thicker at this
point, using more cross-grain plywood laminations to
provide added resistance to splitting. Because a vast
majority of the loading on a case is generated in the
front where the slot protrudes through the keel, this
area can become one of the highest load points in the
entire boat structure. <strong>The</strong>refore, you should make the
front of the slot especially strong to distribute this load
over as much area as possible.
Figure 19-10 illustrates our technique for building and
installing centerboard and daggerboard cases. Begin by
cutting a slot in the keel a little larger than the perimeter
of the case. Lightly bevel the slot, shaping it into a
wedge that tapers from a slightly wider top to a
narrower bottom. Insert the case into the cutout so that
it is flush with the bottom of the keel, plumb, and lined
up with the centerline.
Next, you must make sure that any epoxy you apply
will not drip immediately out of the keel/case joint.
Block the bottom of the case with a piece of wood or
tack a bead of epoxy along the joint line and allow it to
cure. We usually wrap thin plywood in plastic and
staple it to the keel, as shown in Figure 19-10, and find
that this not only prevents oozing but also helps to hold
the case in place. Because the plywood is wrapped in
plastic, it’s easy to remove when the joint has cured.
When the anti-drip device is positioned, pour an epoxy
mixture, slightly thickened with 404 High-Density Filler,
around the outer edges of the case to the full thickness
of the keel. Allow this to cure. To finish the case, apply
a cap and round over its edges. Fiberglass cloth can be
added as desired. We recommend that you apply it to
the corners where the boat and the case meet.
<strong>The</strong> method will result in a perfect structural fit
between the case and the keel, and this will effectively
transfer all loads to the keel. <strong>The</strong> chances of failure of
the joint between the case and the keel have been
minimized, so the possibility that the boat will leak
when it is in the water is greatly reduced.