The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 22 – Stringer-Frame Construction 255
a little easier to sight along the hull because you are
dealing with a solid surface that offers more telltale signs
of humps and hollows that might be present. With the
stringer-frame method, the planing that you do on one
stringer or one frame affects a large surface area in
determining hull fairness. A good fairing batten and
careful eyeballing will help you to achieve good overall
fairness. Develop athwartship fairness by running the
fairing battens at diagonal angles, as well as right angles,
to the stringers. Check longitudinal fairness by sighting
along your permanent stringers. In any areas of possible
irregularity, clamp a large batten onto the offending
stringer to see if it is, in fact, bending fair according to
the batten. <strong>The</strong> favored tools for final fairing operations
are a small hand-held block plane, a smoothing plane
(keep both fine set and very sharp), and an 11" (280mm),
flat wood sanding block with 50-grit sandpaper.
I-Beam Frames
With the stringer-frame system, it’s possible to build a
permanent, I-beam-type frame. <strong>The</strong> benefit of doing
this is that it can greatly stiffen the hull locally while
taking up little interior space. This type of framing is
not usually required throughout a hull, but it can be
very useful in an area of hard curves. We sometimes use
it, too, for deck construction.
<strong>The</strong> I-beam frame has three parts: the load-bearing skin
of the hull, a core composed of lightweight wood
blocking, and an interior load-bearing lamination. <strong>The</strong>
blocking is inserted between stringers in the area of the
frame. <strong>The</strong> lamination, which is formed in place over
the stringers, is placed over stringers and bonded to the
blocking. <strong>The</strong> sizes of blocking and lamination can be
adjusted to handle anticipated loads. Because it is rarely
subjected to high loading, we usually saw the blocking
from low-density wood stock, such as cedar, spruce,
or pine.
One way to build an I-beam frame is to insert the
blocking between the stringers after final fairing of the
stringers but before laminating the hull skin. We suggest
fitting and bonding the blocking between stringers flush
on the interior and protruding enough past the hull
profile for easy fairing for the planking. If you wait until
after the hull is completed and then try to fit the blocking
from the interior, the job is much more difficult.
Blocking faired
to stringers to
accept planking
Planking
Stringers
Spruce or cedar
blocking, rough sawn
to shape and fit to
stringers
Blocking scribed parallel
to the planking and faired
to accept the laminated
cap for the frame
Figure 22-9 Making an I-beam frame by inserting blocking
between stringers.
We usually do not install any blocking until the set-up
has been finally faired. This way, we only have to fair it
into the stringers to which it’s attached. <strong>The</strong> blocking
should also be faired smooth with the stringers on the
inside surface to produce an even surface over which to
laminate the third part of the I-beam. We make up and
permanently install this piece before laminating the hull
surface. (See Figure 22-9)
A second way to form an I-beam frame is shown in
Figure 22-10. With this technique, saw a web frame
flush with the interior of the stringers, let the remaining
plywood serve as blocking, and add a laminated frame
to the interior. This will result in an I-beam that is
probably stronger than the original web frame but takes
up less room.
To make a plywood web frame into an I-beam, fit and
cut notches in the frame. <strong>The</strong>n saw starter cuts about
2" (50mm) long on either side of each notch. Start each
cut at the deepest part of the slot and run it parallel to
the planking towards the next stringer. When you have
finished laminating the hull, check the lines to be sure
they are parallel to the planking, and then use a keyhole
saw to connect them and cut away the excess frame.