down with negative buoyancy. This method provides a controlled and precise 

 method of placement but is hazardous should the tethering cable fail. A 

 module tethered at the bottom and winched down against positive buoyancy 

 provides the best controlled mode with maximum safety. A nylon or poly- 

 propylene rope should be used for the winching operation because of the 

 neutral buoyancy. 



Shore-Based Power Plant Deployment 



The emplacement of a shore-based power plant for an underwater 

 power system involves three phases of effort — namely, construction of the 

 power site, deployment of the power cable, and deployment of the load 

 module. Deployment of the cable would be initiated at the power site and 

 would end at the load module site at sea. Emplacement of the load module 

 at the bottom would be accomplished last. The power cable would be 

 connected to the load module while the module is on the surface over the 

 deployment site. This would enable the complete check-out of the power 

 system before the load module is submerged. Further, this method would 

 assure that the proper amount of cable had been deployed to place the load 

 module at the operational site. 



The cable-laying procedure is basically the same as used for submarine 

 power cables, except in deep water where a cable not capable of supporting 

 itself must be deployed using buoyancy devices. A bottom topography survey 

 is required to establish a cable route, to determine the correct cable length 

 required, and to locate hazardous areas. A cable-laying ship having the 

 required cable storage and handling capacities would be used for cable 

 emplacement. The cable would be layed seaward from the shore with the 

 surf and tidal zone section of the cable buried or placed in ducts 6 feet 

 below the low tide level. Bottom cable laying may be done from a ship 

 having spinal-wound cable tanks, providing the recommended cable tension 

 is maintained by the winches on the ship. Table 1 5 lists the cable-laying 

 capacities of ships which can be used for the cable emplacement. 



When the cable becomes so long that it can no longer support its 

 own weight, cable buoyancy must be provided. A state-of-the-art buoyancy 

 system that could be used to give maximum buoyancy control is 42-lb/ft~^ 

 aviation gasoline. Syntactic foam increases net buoyancy by 2% due to its 

 relative incompressibility and temperature independence. Aviation gasoline 

 decreases in buoyancy by about 8% at a depth of 20,000 feet due to com- 

 pressibility and temperature effects. 



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