A less costly concept for employing wood in buoyancy shapes is 
illustrated in Figure 44. Typically the compressive strength of timber per- 
pendicular to the grain is many times less than that parallel to the grain. 
For coast-type Douglas fir at 12% moisture content, for instance, the 
relative values-are 870 to 7,430 psi, respectively, a ratio of over 1 to 8 
(USDA, 1955). This suggests the fabrication configuration shown in 
Figure 44, in which the fibers are selectively oriented to take advantage 
of the anisotropy. This relatively inexpensive wood with minimum water- 
proofing of sheathing should be useful at least 12,000 feet in the ocean. 
Other even more advantageous arrangements could probably be developed. 
For one thing, it appears that some collective reinforcement should be pos- 
sible with suitable preferred fiber orientations, so that the measured stiffness 
in the complex structures would be greater than calculations based on indi- 
vidual components. This phenomenon is referred to as “jamming.” 
A recent development in buoyancy, not yet fully tested in a pressure 
environment, is described by Madden (1970). Figure 45 from that source 
shows closely packed spheres formed from brazed hemispheres in a possible 
replacement for the well-established honeycomb core material developed for 
industrial and aerospace applications. The material offers promise both as a 
buoyancy and a structural material. 
end grain 
end grain 
(typical of 
all faces) 
Figure 44. Composite wood buoyancy shape, with end grain exposed on all 
faces for greater strength. 
56 
