The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 23 – Strip Plank Laminated Veneer and Strip Composite Construction 275
Figure 23-12 Two stripper canoes built by Herschel Payne. Western red cedar and WEST SYSTEM epoxy were used for both boats.
<strong>The</strong> 15' (4.5m) model weights 32 lb (12.8kg) and the 18' (5.5m) model weighs 48 lb (21.6kg) .
planking with a bead and cove feature, which assists in
planking installation and alignment.
In the 1980s, we did some tests to evaluate the relative
effects of various weights and numbers of layers of glass
cloth, and to explore the relationships between these
and wood core thickness in terms of stiffness, ultimate
strength, and weight. More comprehensive tests were
conducted in 1998. Our results provide preliminary
suggestions on the best ways to build strength and stiffness
into stripper hulls.
Glass fabric is used in strip composite construction to
supply cross-grain strength to wood planking. In more
traditional methods, closely spaced ribs serve this
function. While two layers of cloth over 1 ⁄4" (6mm)
planking are sufficient to support a canoe, this schedule
is inadequate for larger hulls. Two approaches to
increasing strength and stiffness are adding extra layers
of cloth and increasing planking thickness. Our testing
indicates that, up to a certain point, adding more fiberglass
to a hull justifies itself by increasing strength and
stiffness disproportionately to the increase in weight.
Figure 23-13 shows data that compares four thicknesses
of cedar strip panels reinforced with various layers and
weights of woven fiberglass fabric. Data on three thicknesses
of marine plywood are provided for comparison.
This chart is intended to rank the various panel and
Panel thickness
cedar strip
Fiberglass
schedule
Weight
ounces/sq. ft.
Inches of
deflection
Pounds to
failure
3/16" 1 layer 4 oz 6.5 .85 162
3/16" 2 layer 4 oz 8.8 .82 309
3/16" 1 layer 6 oz 8.0 .73 214
3/16" 2 layer 6 oz 10.6 .90 500
1/4" 1 layer 4 oz 9.0 .45 150
1/4" 2 layer 4 oz 10.3 .70 375
1/4" 1 layer 6 oz 9.8 .49 221
1/4" 2 layer 6 oz 12.3 .58 450
5/16" 1 layer 4 oz 10.6 .43 188
5/16" 2 layer 4 oz 12.6 .66 499
5/16" 1 layer 6 oz 11.6 .48 300
5/16" 2 layer 6 oz 14.1 .44 500
3/8" 1 layer 4 oz 12.7 .42 250
3/8" 2 layer 4 oz 14.1 .66 675
3/8" 1 layer 6 oz 13.1 .32 298
3/8" 2 layer 6 oz 15.4 .51 823
marine plywood
5/32” 1 layer 4 oz 8.5 1.47 211
7/32” 1 layer 4 oz 10.9 1.01 325
1/4” 1 layer 4 oz 12.8 .79 429
5/32” no glass 6.9 1.60 45
7/32” no glass 9.1 1.20 149
1/4” no glass 10.7 .63 225
Figure 23-13 Stiffness and strength of panels reinforced with
various fiberglass fabrics vs. panel weight. Stiffness is shown
as Inches of deflection and strength is shown as Pounds to
failure.