312 ENGINEERING EVALUATION 



access hatch was installed in the top of the hull amidship. This hatch was also of a submarine 

 type, 30 in. in diameter, and provided access to the Sealab II interior while in the water but 

 still on the surface. 



Entry Trunk 



A trunk 8 x 8 ft by 2-1/2 ft deep was installed below the hull around the main entry hatch. 

 Since the main entry hatch was to remain open at all times while Sealab Ii was inhabited, the 

 entry trunk was designed to provide a displacement volume to compensate for seawater pres- 

 sure variation caused by tidal action, in addition to the expected internal gas pressure fluctua- 

 tions. It was determined that the predicted tidal range of nine feet would cause a 2-1/2-ft ex- 

 cursion of the water level in the entry trunk. However, it was necessary to keep the gas volume 

 of the entry trunli (approximately six tons displacement) small so as to reduce the tipping 

 moment create by this increased buoyancy at the stern of the craft. Compensation by ballast- 

 ing from the si -face was not considered feasible. 



Shark Cage 



A protective enclosure of expanded metal was built around the entry trunk. Approximately 

 8 ft wide by 12 ft long, this enclosure provided a protected observation point or retreat in the 

 event that sharks were in the area. A dutch door, 4 ft wide by 6 ft high, was provided to permit 

 access if the lower portion of the door was embedded in the sea bottom. The lower foot of the 

 shark cage was made of chain to allow conformity with a possible uneven bottom. 



Support Structure 



The support structure was designed to provide a clearance of 6-1/2 ft between the hull and 

 the sea bottom. Bottom bearing plates (two each 3 ft x 18 ft) were installed to provide a maxi- 

 mum seafloor bearing stress of 300 psi. On-site tests of the seafloor had indicated a minimum 

 soil-bearing strength of 1300 psi. 



The use of leveling jacks was considered but was rejected because of their cost and the 

 time required to provide them. Site surveys indicated a maximum bottom slope of 5 percent 

 (approximately 3 degrees) and no need for such jacks. 



Spades were installed at each end of each bearing plate, so as to penetrate the bottom and 

 reduce the possibility of lateral movement. 



Hull Penetrations 



All hull penetrations for gas lines, water line, sanitary drains, and cables, were located as 

 near deck level as possible to minimize loss of atmosphere and flooding of Sealab II in the event 

 of external line damage. These penetrations were sealed by double stuffing tubes, or the pipes 

 were welded to the hull. Hull penetrations were optimally located to minimize the lengths of 

 high-pressure lines inside Sealab II. A 10-in. pipe was installed through the bottom near the 

 a:t'j_ end of the lab space to accommodate power leads for the outside diving lights and signal 

 leads for the benthlc lab, an underwater data multiplexing and telemetering system developed 

 by the Marine Physical Laboratory of the University of California. This pipe extended from 

 the horizontal centerline of the hull to a point 2-1/2 ft below the hull, so that the required ca- 

 bles could be installed upon removal of a pressure-tight bolted flange after habitation of Sea- 

 lab II. A 3 -in. pipe was installed inside the 10-in. pipe to provide shielding between the diving 

 light power leads and the benthic lab signal leads. Bilge drains with manually operated valves 

 were provided to allow draining the bilges overboard while Sealab II was on bottom. 



