ENGINEERING EVALUATION 313 



Variable Ballast 



The upper portion of the hull volume (3 ft deep by full hull length) was utilized for water 

 ballast. This volume was divided into three separate tanks (No. 1, forward; No. 2, amidships, 

 and No. 3, aft). A fourth tank was provided by the "conning tower," which also served as a 

 breakwater for the surface access hatch. The internal tanks were designed to withstand a 

 pressure differential of 15 psi across their flat bottoms. Internal ballast tanks were utilized 

 for several reasons: 



1. To reduce internal gas volume and consequently the total volume of helium required 

 for charging. 



2. To reduce the virtual mass of the entire structure in water by eliminating external 

 ballast tanks. 



3. External ballast tanks would have severely limited the field of view from the Sealab II 

 viewing ports towards the sea bottom. These ballast tanks were utilized to provide 



a. Adequate positive buoyancy for surface tow and systems checkout. 



b. Negative buoyancy for lowering and raising. 



c. Adequate negative buoyancy for necessary stability on bottom. A maximum negative 

 buoyancy of 13 tons was required to provide bottom stability in a maximum athwartship cur- 

 rent of 2 knots. 



Fixed Ballast 



Fixed ballast was provided by: 



1. Concrete inside the hull to deck level except in the entryway. 



2. Lead weights secured in the ballast tray underneath the hull. 



Lead pigs in ballast trays located fore and aft under the topside walkways were utilized to pro- 

 vide final fore and aft trim. 



Hull Insulation 



The insulation used in Sealab II was Navy "standard stock" submarine corkboard in one- 

 inch-thick boards. The coefficient of thermal conductivity (k) for this material at standard 

 atmosphere is 0.025 Btu/hr-ft-°F. The overhead was insulated with one inch and the hull sides 

 with two inches of this corkboard. No insulating material was utilized on the concrete deck 

 except carpet, since radiant heating cables were installed in the concrete. The thermal con- 

 ductivity (k) of helium is 0.090 Btu/hr-ft-°F, six times that of air. Since the insulating mate- 

 rial was to be permeated by the helium at the ambient pressure of approximately 102 psia, the 

 theoretical coefficient of thermal conductivity (k) for the cork insulation under ambient condi- 

 tions was calculated to be 0.100 Btu/hr-ft-°F. This value of k was then utilized to calculate 

 the expected heat losses in Sealab II, as shown in Appendix B. 



UMBILICAL CORD 



An umbilical cord provided the necessary utilities from the support vessel to Sealab n. 

 The original umbilical cord consisted of five components, providing: 



1. Alternate electrical power 



2. Communication circuits 



