suffice for surface plant mooring systems. Alternative methods would be to 

 grout the anchor into the bottom or use explosives to drive it in. The 

 advantages of these methods are high reliability and holding power that 

 is not directionally dependent. However, the state of the art in deploying 

 grouted pile anchors at depths of interest is not sufficiently advanced for use 

 on the surface plant mooring system. 



Table 8. Holding Power and Weight of Conventional Anchors 



Type of 

 Anchor 



Weight 

 (lb) 



Maximum Holding 



Power in Sand 



(lb) 



LWT 



LWT 



wedge block 



LWT 

 wedge block 



LWT 



wedge block 



EELLS 



4,000 

 6,000 



10,000 



25,000 

 8,000 



75,000 

 106,000 



175,000 



430,000 

 80,000 



Conventional anchors of the LWT wedge block design were selected 

 for the surface plant mooring system. An electronic device that can be 

 attached to the anchor is available to determine when the anchor has dug 

 into the bottom. 



Wire rope manufacturers and the petroleum industry are significantly 

 advancing the state of the art of undersea wire rope. Stainless steel wire rope 

 in underwater applications is susceptible to chloride stress corrosion. Stainless 

 steel ropes have failed as early as 4 to 5 months after deployment. Programs 

 to use plain steel and zinc-coated steel indicate that maximum deployment 

 time for these ropes is 3 years. Cathodic protection for deep ocean applica- 

 tions is developmental and not available. For purposes of the study, a 

 polyurethane-clad, three-strand, torque-balanced steel rope was selected for 

 a 5-year deployment life. Swivels must be provided for terminating the ends 

 of the wire rope so that end fixing can be avoided. Figure 14 is a conceptional 

 sketch showing a method for attaching a wire rope to a terminal swivel socket. 

 Many wire rope moorings are suspected of fatigue failure. Therefore, vibra- 

 tion dampers should be provided on the terminal swivel. 



43 



