A syntactic foam material weighing 44 Ib/ft"^ in air was considered for 

 buoyancy floats. This foam is available and has well-established properties. 



Typical buoy configurations used in the study are shown in Figure 21. 

 Each of the configurations is shaped like a clam shell to minimize drag forces 

 on the buoyancy units. 



Figure 22 shows the support requirements for a representative number 

 of cables at their respective depths. The number of aluminum spheres required 

 for each float device is noted in Figure 22. 



Both the syntactic float and aluminum sphere float are considered to 

 be within the present state of the art and can be procured in a reasonable 

 time. Aluminum spheres were considered the most cost effective buoys for 

 the cable support system. 



There are two cable suspension configurations suitable for an 

 underwater power transmission system — namely, a taut line configuration 

 and a normal catenary configuration. A taut line configuration is shown in 

 Figure 23. One or more buoys are suspended along the cable length. The 

 total buoyancy of the buoys is greater than the displacement weight of the 

 cable so that a positive vertical force is generated along the cable. Attached 

 to the uppermost buoy is a pendant cable which is attached to the surface 

 unit. The uppermost buoy was placed at a 2,000-foot depth for all concepts 

 evaluated. 



When the surface unit excursion is at its minimum point, it was 

 assumed that the pendant cable is hanging essentially vertical, with one end 

 supported by the surface unit and the other end by the upper-most buoy at 

 2,000 feet. For a load module at a 20,000-foot depth, the length of the 

 pendant cable was postulated to approach 20,000 feet. With this length the 

 pendant cable would hang to about 1 1 ,000 feet when the surface unit is above 

 the load module. The minimum excursion point in an actual design must be 

 displaced a horizontal distance from the vertical centerline of the load module 

 to prevent the cable from entangling with the mooring legs or wrapping around 

 itself. 



A catenary configuration is shown in Figure 24. As noted, the 

 buoyancy units are spaced along the cable at discrete points to maintain safe 

 tensile levels in the cable armor. The surface unit excursion poses no serious 

 problem in catenary configuration. However, as the surface unit moves from 

 its maximum excursion point, the cable will abrade on the bottom. To pre- 

 vent this, a buoyancy unit must be installed so that at the innermost portion 

 of the excursion the total depth of cable is less than that of the load module. 

 With a load module at 20,000 feet, the surface excursion is approximately 

 18,000 feet. Allowing the innermost portion of the excursion range to be 

 directly above the load module, the buoyancy unit would be placed some 

 7,000 feet above the bottom. 



62 



