impede the natural action of the tether. Temperature extremes could damage 

 tethers if inadequate materials are used. For ease of handling, the riser 

 should be flexible enough to be coiled within a diameter equal to that of the 

 associated float. To ensure only minimal influence on float performance, the 

 tether termination assembly should be kept to about 10 percent of the dry 

 weight of the float (Johnson, 1977). 



b. Prototype Designs . The Naval Undersea Center investigated three dif- 

 ferent prototype tether termination assemblies, each using a 5-f oot-diameter 

 float with 3,000 pounds of buoyancy. 



(1) Ball and Socket Termination Assembly . In this tether termination 

 assembly concept, the ball was cast phenolic resin, and the socket was ultra- 

 high molecular-weight polyethylene. The materials were chosen for compata- 

 bility, noncorrosive characteristics, availability, toughness, and excellent 

 abrasion resistance. The phenolic balls are available commercially in a range 

 of sizes. The high density polyethylene with extreme abrasion resistance is 

 available for forming or machining the sockets. The riser material (tether) 

 is Sampson very low stretch, single-braid polyester rope (7/8-inch diameter), 

 which is relatively new commercially. 



(2) Booted Assembly for Wire Rope Riser . This concept uses steel 

 torque-balanced Amgal polyethylene- jacketed wire rope (1/2-inch diameter). 

 The riser is swaged into an open socket which supports all tensil loads. 

 Length of the swage is eight rope diameters, a figure proven over the years to 

 be optimal for swaged sockets. The slip-on boot is designed to control flex- 

 ure, so that under 4,000 pounds of tension the riser will have no curvature 

 with less than a 12-inch radius. A seal is provided by the boot to prevent 

 seawater from entering under the riser jacket. No part of the tensil loading 

 is supported by the boot. 



(3) Booted Assembly for Synthetic Rope Riser . Lane Instrument 

 Company, San Diego, California, specifically designed a tether termination 

 assembly of the booted type for use with synthetic rope. The Sampson very low 

 stretch, single-braid polyester rope was used as the riser because of its 

 nonhocking property. It is easy to handle, can be spliced quickly, and has a 

 high modulus of elasticity (less than 3 percent elongation at design load). 

 The riser (7/8-inch diameter) terminates inside the boot, using an eye splice 

 through an eyebolt, which in turn is threaded into the bottom plate of the 

 assembly. The threads are then locked with a setscrew placed along the margin 

 of the eyebolt and bottom plate threads, and the region is sealed with epoxy 

 to prevent corrosion. The boot design for this assembly was the same as was 

 used in the wire rope assembly; the boot was molded in place instead of being 

 slipped on. 



In February 1976, twelve of these tether configurations, using eight 

 1 ,200-pound-buoyancy and four 800-pound-buoyancy floats, were installed at a 

 test site off Imperial Beach, California. There were no failures after a year 

 in the ocean environment. These tests provided a good understanding of the 

 long-term effects of corrosion, fouling, tensil loading, tensil cycling, elon- 

 gation, and other similar forces. Little is known, however, which can help 

 predict the flexure life of a specific tether termination assembly for a given 

 set of operating requirements. Both laboratory and ocean testing are cur- 

 rently underway, and the results are expected to permit more efficient designs 

 of tether termination assemblies. 



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