Gas Generators. A significant amount of thought and development 

 is being given to systems which expel water from hard-shell containers with 

 a gas. It has been ascertained that air pumped from the surface to displace 

 water is not feasible at depths over 1 ,000 feet. Thus, most effort has been 

 concentrated in the development of gas generators. The Navy Underwater 

 Weapons Center (NUWC) has successfully conducted feasibility tests using 

 hydrazine fuel with a catalyst which causes spontaneous combustion (see 

 Reference 10, for example). The gas generator, mounted directly on the 

 buoy, provides a controllable decomposition of the gas and, consequently, 

 a controllable buoyancy system. 



At present, gas generating units have limited depth and load capabili- 

 ties. It may be concluded with reasonable confidence that gas generators 

 have not yet reached the stage of development that makes them feasible for 

 heavy lift. Moreover, considering the cost of the hydrazine and the dangers 

 associated with its use, there is some question whether they are even desirable 

 for the heavy-lift project. 



Metal Alloy Buoys. The addition of a mechanism for flooding the 

 metal buoys previously discussed is considered the most desirable of the 

 variable buoyancy systems and, therefore, the most desirable Of all sources 

 of buoyancy. 



Included in Reference 9 is a comprehensive examination of ring- 

 stiffened cylinders made of high-strength steel. The basic configuration 

 investigated consists of a series of cylindrical hulls of uniform size placed 

 end-to-end, the number of hulls depending on the buoyancy required. Each 

 hull can be flooded as necessary to decrease the buoyancy of the entire 

 string to the condition where the remaining unflooded hulls provide just 

 enough buoyancy to lift the entire system upward at an acceptable rate. An 

 important design input for the variable buoyancy system is the conclusion 

 reached earlier that the 3-1/2-inch diameter cable is a near optimum 

 compromise on a strength-diameter basis. 



One of the primary advantages of the cylindrical hull, modular-type 

 buoyancy system is that any load can be lifted with only one cable by simply 

 adding buoyancy units to the load. The uncertainties and possibilities of 

 cable entanglement are thereby eliminated. As an example, the 3-1/2-inch, 

 100-ton capacity cable can be used to lift a 600-ton load by first attaching 

 500 tons of buoyancy modules to the load. Once the load is placed on the 

 bottom, some of the buoyancy modules can be flooded, so the total downward 

 force on the cable is enough to prevent kinking and still less than 100 tons. 



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