The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

250 Hull Construction Methods
plank methods, you notch them into all of the frames
and bulkheads so that they are flush with the outer
edges of these parts. Stringers are also let into the back
of the stem, with their outer edges flush with the faired
stem surface. Layers of hull skin are bonded to all of
these parts and help to join them.
Stringers for Stringer-Frame Construction
Stringers, like frames, serve two functions. <strong>The</strong>y, too,
form a reasonably substantial mold shape as the hull is
built and support it when it is finished. It’s difficult to
temporarily reinforce stringers for laminating, so mold
requirements supersede the requirements of the
completed hull. Chances are that you will end up using
more stringers than the structure actually needs in order
to have a decent mold. Stringers may, however, be
planed to smaller size after the hull skin has been
laminated.
<strong>The</strong> main requirement of a stringer is that it not bend
or deflect as veneer or plywood is bent around it during
laminating. To minimize distortion, we always set
stringers on edge, with the smaller dimension, or thickness,
touching the skin, while the larger dimension, or
depth, extends inward. A typical stringer for a 40'
(12.2m) boat is 11 ⁄2" (38mm) deep and 3 ⁄4" (18mm)
thick. We attach the 3 ⁄4" side to the skin and run the 11 ⁄2"
side towards the interior. This makes a T-section, which
gives the completed hull great stiffness and strength. If
the stringer was attached to the skin by its 11 ⁄2" side, it
would provide only about one third of the stiffness it
offers in the 3 ⁄4" dimension, and it would probably deform
during laminating. This might lead to an unfair hull.
Since you will be stapling veneer and plywood to the
edge of the stringer, it must be thick enough to permit
stapling without a lot of misses. Although it’s easy for a
staple to miss even a thick stringer and missed staples
can be removed before the next layer is applied, 3 ⁄4"
(18mm) is a practical stringer thickness for stapling. We
regularly, however, go down to 5 ⁄8" (15mm) with little
difficulty. Thinner stringers can be used, but may
require very time-consuming and exact measuring to
avoid misses.
Another consideration determining stringer size is the
ability of the stringer to bend around the most severe
curves in the hull shape. In certain situations, it may be
necessary to laminate stringers out of two or three pieces
to negotiate a curve. If so, use the set-up as a temporary
form on which to clamp and form the laminate until
the adhesive cures. <strong>The</strong>n remove the laminated stringer
from the set-up and prefinish it prior to reinstalling it
into the set-up. <strong>The</strong> laminated stringer has the big
advantage in that it is sure to be very stiff and will resist
deflection during the veneer laminating process.
Because of the variables involved, it is difficult to give
advice as to stringer size adequate to resist deflection
during laminating. Usually you can determine this for
yourself by creating a mock-up situation where you set
a given size stringer between two points that would
approximate the frame spacing. By bending some of
your laminate stock over this stringer, you can get a
general idea as to whether or not it will be adequate. As
a general guideline, a 11 ⁄2" � 3 ⁄4" (38mm � 18mm)
stringer is adequate for most laminating situations
when used on frame spacings up to 24" (600mm).
<strong>The</strong> next decision is the spacing of the stringer along
the frames. Initially it isn’t a question of how many
stringers are needed in the completed hull, but of the
minimum number of stringers necessary for proper
laminating to take place. Once again, the needs of the
hull structure and those of the mold are different.
<strong>The</strong> main factor that determines stringer spacing is the
shape of the hull itself. In areas with more curve, tighter
spacing of stringers may be needed to define the hull
shape properly, while flatter areas can rely on fewer
Figure 22-1 Rogue Wave’s main hull set-up with stringers
installed and ready for planking.