332 ENGINEERING EVALUATION 



In addition, a hydraulic pump could be installed to provide final trim, if necessary. This type 

 of system would be relatively fail-safe; loss of hydraulic fluid would only cause loss of trim, 

 since the rams at full extension or collapse still provide a safe mechanical connection. The 

 support or hold-down structure should be designed such that the height of the Sealab hull above 

 bottom is minimized if visual observation of the bottom from inside Sealab is to be a consid- 

 eration. 



Variable Ballast — In view of the problems encountered with the internal ballasting ar- 

 rangement, and in order to provide additional usable internal volume, an external variable 

 ballast system should be considered. The internal volume of the present ballast tanks could 

 then be utilized as additional equipment and stowage space. 



Hull Insulation — Since the cork insulation used in Sealab II functioned quite successfully, 

 it would seem to be the logical choice for use in Sealab HE. Other insulating materials are 

 available, such as urethane foams, which offer increased thermal efficiencies (2 to 1) over 

 cork at standard conditions. However, in the Sealab environment the theoretical efficiency of 

 the foam is only 13 percent better than cork. In addition, one must carefully consider the dis- 

 advantages of the foam, such as increased cost and possible toxicity. 



The Sealab hull could be insulated externally to eliminate the reduced thermal efficiency 

 caused by the Sealab atmosphere. However, some new problems would be encountered; the 

 material used must be relatively impermeable to water, must have the necessary compressive 

 strength to withstand the ambient water pressure, and must be relatively rugged to withstand 

 normal handling of the Sealab. 



The only insulation system which would seem to eliminate the effects of both the Sealab 

 atmosphere and the outside water would be a double-shell arrangement similar to the "vacuum- 

 bottle" principle. This system is considered not feasible from the standpoint of economic 

 considerations. 



Umbilical Cord 



The umbilical cord should be designed as a composite unit. The design should provide for 

 a smaller size, reduced weight, increased ruggedness, and self -buoyancy. A small reel should 

 be provided for storage and improved handling of the umbilical, and Sealab hull connections 

 should be provided to permit replacement of the entire umbilical when needed. A thorough re- 

 view of conductor requirements should be made so that an adequate number may be provided. 

 A generous number of spare condactors should also be provided for backup and nonessential 

 use. 



Systems 



Electrical System — As has been pointed out, the electrical system as a whole was very 

 satisfactory. It is recommended *hat the basic system be retained and that the following 

 changes be made. 



1. Replace the present thermal-magnetic circuit breakers with hydraulic -magnetic type. 

 These circuit breakers are commercially available but would require pressure testing and 

 possible modification of the hydraulic tube. This type breaker is not temperature sensitive. 



2. Install multiple plug strips along the top of all lab benches. Connect the plug strips to 

 existing circuits with portable cable and twist-lock plugs and receptacles. 



3. Redesign the interior lighting system to provide two levels of lighting, one for photog- 

 raphy and one for normal use. Quartz-iodine lamps should be considered, since they are ca- 

 pable of withstanding the ambient pressures expected. They can also be dimmed with com- 

 mercially available dimmers; however, tests will be required to determine the effect of the 

 helium-rich atmosphere on the bu'b temperature. The iodine cycle of the quartz-iodine lamp 

 will not function below a certain temperature. To prevent burning the vidicon tubes of the TV 



