A typical single-leg flexible anchor also incorporates a weak link near the 

 anchor to permit recovery of practically the entire line in case the anchor 

 snags. 



The single-leg flexible anchor is used to secure a ship for relatively 

 short periods of time. The ship can drift considerable distances, conceivably 

 to any point in a circle where the center is directly over the anchor and the 

 radius is equal to 1 .3 times the depth. 



The liSNS Josiah W. Gibbs, a 2,800 ton vessel, has been anchored in 

 depths to 1 8,000 feet with a single-leg flexible system. In one instance the 

 ship, anchored in 18,000 feet of water, did not experience any discernible 

 drift in winds of 37 knots. The cable was 6x19 galvanized plow steel with 

 a wire rope core. Significant here is the fact that the anchoring system was 

 subjected to a thorough mathematical analysis — nothing was left solely to 

 experience. Unfortunately, there is nothing in the literature which reveals 

 whether this particular anchoring is typical; it would appear that it is not. 



Multileg Flexible Anchorage System. It is evident from the literature 

 that anchorage systems employing more than one leg are needed to achieve 

 a sufficient degree of permanency for surface vessels. Multileg systems are 

 fairly complex in shallow water and the complexity increases "at a geometric 

 rate with depth." (Reference 25, p. 4.15.) As of late 1965, the maximum 

 depth for a permanent installation of this type was felt to be in the neighbor- 

 hood of 500 feet. Little has happened since that time to alter this situation. 



A noteworthy example of a deep-mooring system is TOTO II. It is 

 a three-legged mooring in 5,500 feet of water. This installation is quite 

 involved and requires considerable amounts of time and support to 

 accomplish, in the TOTO 1 1 system, a cruiser size vessel can be held on one 

 heading and in position within a 50-foot radius. 



Bottom-Rest Anchorage Systems. Bottom-rest systems are negatively 

 buoyant structures that rest on the ocean floor. Offshore oil well rigs and 

 man-made islands are typical of structures of this type. At present, most of 

 these installations are in water depths of approximately 200 feet. It is 

 unrealistic to suppose that a bottom-rest structure could be employed for 

 this project. 



