328 P. Mandel 
is to some extent compensated for by the compressibility of water. In relatively-thin-hulled 
shallow-depth submarines, however, the loss in volume represents a hull compressibility 
which is greater than the compressibility of the surrounding sea water. As a consequence 
the hull becomes less buoyant as it dives, which is an inherently unstable condition. Thus, 
a thin-hulled submarine that is neutrally buoyant near the surface must by some means dis- 
charge ballast at deeper depth in order to attain neutral buoyancy again at that depth. 
Contrary to this situation, the thick hull of the Aluminaut is less compressible than 
water. As a result the boat becomes lighter as it sinks. Thus theoretically it should be 
possible when it is desired to dive the Aluminaut to its operating depth to take in a precise 
amount of excess ballast so that the Aluminaut has negative buoyancy near the surface. 
Without further intake or discharge of ballast the boat should then sink slowly to its operat- 
ing depth where it will be in perfect equilibrium if the proper amount of excess ballast was 
initially taken aboard. 
Particulars are shown in Table 5. The density of water at 15,000-foot submergence is 
about 2 percent greater than its density near the surface. Thus an incompressible hull would 
gain about 2 percent of its near surface buoyancy at a depth of 15,000 feet. On the other 
hand, if a thin-hulled submarine such as are now designed for shallow depths could be 
designed somehow to accept 15,000-foot submergence, it would lose about 5-1/2 percent of 
its near surface volume at that submergence and thus lose about 3-1/2 percent of its near 
surface buoyancy. The Aluminaut pressure hull is closer to the incompressible hull in this 
respect and loses only about 0.5 percent of its near surface volume at 15,000-foot submer- 
gence. Thus, it gains 1-1/2 percent of its near surface buoyancy at 15,000 feet. However, 
the overall compressibility of the entire Aluminaut configuration is considerably greater 
than 0.5 percent, primarily because the pressure-equalized silicone fluid in the stern cap- 
sule is itself much more compressible than water. It is estimated that the compressibility 
of the entire Aluminaut configuration is about 1-1/2 percent; thus it gains only about 0.5 
percent of its near surface buoyancy at 15,000 feet. However, this calculation is believed 
to be too sensitive to subtle influence to be entirely depended upon, and must be carefully 
checked during the initial dive of the boat itself. 
Table 5 
Effects of Compressibility 
Ratio of Water | Ratio of Hull 
eee Density at Volume at Gain 
Compressibility of Hull Depth and Depth and or loss 
oN Water Density | Hull Volume | Buoyancy 
at Surface at Surface 
Incompressible hull 1% gain 
Incompressible hull 2% gain 
Hull as compressible as water 0 
Hull as compressible as water 0 
Thin hull submarine 1.5% loss 
Thin hull submarine 3.5% loss 
Aluminaut, pressure hull only 1.5% gain 
Aluminaut, entire configuration 0.5% gain 
