SECT. 5] DEEP-SEA ANCHORING AND MOORING 527 



bottoms of slopes exceeding about twenty degrees, and anchors with hooks, 

 flukes or grapnels must be used. 



The anchor must be designed so that stability to overturning is acceptable. 

 This requires a flat anchor with a low point of attachment. 



7. Fittings 



For moorings designed to last as long as possible, special shackles, insulated 

 by micarta sleeves to minimize electrolytic action in the mooring components, 

 have been used. The relative efficiency of such measures for this purpose is not 

 known exactly but it is apparent that, as a minimum, it prolongs the life of 

 connecting shackles by preventing abrasive damage to the protective zinc 

 coating. 



8. Performance 



A well-designed mooring of this nature will have a life of many months, 

 barring accident, in the conditions of the Central Pacific. Surface floats and 

 instrument strings can be exchanged without disturbing the basic mooring. 



By proper design, excursion (i.e. horizontal motion) ordinarily can be main- 

 tained at less than 10% of the depth, or about 1% if critically important, under 

 extremes of weather. Dip, that is vertical motion, can easily be maintained 

 below 1% of the depth. 



Cost of such mooring, exclusive of instrumentation and ship time, is about 

 $700 for mooring components and an equal amount for the surface float. 



References 



Bascom, W. N., 1953. A deep-sea instrument station. Scripps Inst. Oceanog. Rep., 53-38. 



Isaacs, J. D., James L. Faughn, George B. Schick and Marston C. Sargent, 1962. Deep- 

 sea mooring. Bull. Scripps Inst. Oceanog. Univ. Calif. In press. 



Isaacs, J. D. and G. B. Schick, 1960. Deep-sea free -instrument vehicle. Deep-Sea Res., 7, 

 61-67. 



