Conclusions. The limited load capacity of the largest cable feasible 

 for this project, combined with the necessity of using a multicable approach, 

 has relegated the cable suspension systems to a position inferior to pipe string 

 systems. Probably the greatest drawback is the high degree of uncertainty 

 that must be assigned to cable systems in general. The low fatigue life of 

 cable, the possibility of cable entanglement, and the precise control required 

 during an operation all help make the nature of cable systems unsure. 



Buoyancy Systems 



The surface-independent systems require that an external source of 

 buoyancy be added to the load. The buoyancy-assist cable systems are also 

 dependent on some source of buoyancy to help reduce the tensions in the 

 cable(s). Hence, an important part of this study was the investigation of 

 sources of buoyancy. 



There are two types of buoyancy systems: variable and nonvariable. 

 The buoyancy of the variable systems can be adjusted to a predetermined 

 value and can continually compensate for changes in water density and 

 temperature as the lifting and lowering operations take place. There is no 

 provision for changing the buoyancy of the nonvariable systems once the 

 operation begins. Both types of buoyancy sources are discussed in detail in 

 Reference 9. Also presented in this reference are the results of a thorough 

 analysis of buoyant-assist cable systems. 



Nonvariable Buoyancy. There are four possible approaches to 

 supplying a nonvariable buoyancy source to the load: 



1. Syntactic foam 



2. Hollow buoyancy objects 



3. Liquids in containers 



4. Metal alloy pressure vessels 



For the last two concepts, relatively minor changes in the design would 

 provide a variable buoyancy system. 



Syntactic foam is a composite of small hollow spheres (usually glass) 

 in an epoxy resin binder. The formulas for the better syntactic foams are 

 proprietary information. Syntactic foams can return 0.6 pound buoyancy 

 per 1 pound of foam, and can be used in depths up to 20,000 feet with little 

 or no loss of buoyancy. They are, however, expensive; a cost of $5 to $6 per 

 pound of foam is not unusual. Disregarding cost, syntactic foam is a most 

 attractive nonvariable buoyancy material. 



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