ENGINEERING EVALUATION 315 



Provision was made to flood each tank space at its bottom, and all tanks were vented 

 through individual valves to a common manifold which led to a master vent valve. The mani- 

 fold was further connected to the main cylinder through a valve to provide pressure equaliza- 

 tion between any tank and the habitation space. The manifold was also connected to the entry 

 skirt to provide for blowing the skirt and equalizing the skirt with the habitation space. 



The weights and centers of gravity were calculated for all operational conditions, and a 

 surface waterline was established. After all gear was aboard in its proper location, Sealab II 

 was put into the water dockside, and the pig ballast under the topside walkway was adjusted to 

 attain the pre-established water line. 



With all ballast tanks dry and the entry skirt flooded and hatches sealed, Sealab II was in 

 condition to go to sea with buoyancy and stability as required for towing. On site, the conning- 

 tower hatches could be opened to allow final checkout of equipment. The conning tower pro- 

 vided the necessary freeboard to prevent flooding of the habitation space by wave action. Be- 

 fore the habitation space was pressurized with its atmosphere, the end tanks overhead could be 

 flooded. In this condition, buoyancy with hatches sealed was adequate to keep Sealab II afloat 

 while it was pressurized. With the end tanks full, all flood valves were to be closed and in- 

 ternal tanks were to be opened to the vent manifold, with the manifold open to the habitation 

 space. In this way, during atmosphere pressurization, no pressure differential would exist on 

 the boundary between the habitation space and the internal tanks. After pressurizing of the 

 hull to slightly below the final pressure, the conning tower could be flooded to give the system 

 negative buoyancy for lowering. Once on the bottom, the center overhead tank was flooded to 

 stabilize Sealab II on the bottom and allow blowing of the entry trunk. While the center tank 

 was flooding, its vent could be opened via the manifold to the interior; the vented gas then gave 

 the habitation space its final desired pressure. 



For return to surface after all hatches were sealed, provision was made for blowing the 

 center overhead tank and hoisting to surface. 



Electrical System 



Supply Voltage — The electrical distribution system used in Sealab II was 450 volts three- 

 phase and 208/120 volts three-phase with ungrounded neutral. The system had a total capacity 

 of 75 kva. Normal power was supplied from shore at 4160 volts three-phase by an underwater 

 cable. The 4160-volt power terminated in an underwater transformer bank and was stepped 

 down and supplied to Sealab at 450 volts three-phase. Alternate power for use in case of nor- 

 mal power failure was supplied from the support vessel at 450 volts three-phase through a 

 cable in the umbilical cord. Both cables entered the hull through pressure-proof stuffing tubes 

 near the bottom of the hull. Both supplies were connected to the main power-distribution panel 

 through 100-ampere three-pole circuit breakers. A mechanical interlock assembly was pro- 

 vided so that both supplies could not be used at the same time. Indicator lights on the main 

 panel indicated from which source power was available. 



Utilization Voltages — The electrical loads in Sealab II utilized the following voltages: 



1. 440 volts, three-phase 



2. 208 volts, three-phase 



3. 208 volts, single-phase 



4. 120 volts, single-phase. 



A transformer bank consisting of three 25-kva single-phase transformers connected delta-wye 

 supplied the 208/120-volt power. The transformer bank was installed in a gas-tight compart- 

 ment to prevent atmospheric contamination in case of transformer overheating. The hull 

 formed one side of the compartment and was left uninsulated to aid in cooling the compartment. 

 A fan was installed in the compartment to improve air circulation and provide additional cool- 

 ing. A remote -reading thermometer was also installed so that the interior temperature of the 

 enclosure could be monitored. The transformer bank and all equipment operating on 440 volts 

 were supplied from the main distribution panel. Three low-voltage power panels were supplied 

 from the load side of the transformer bank. Two of the panels supplied all of the 120 -volt 



