24. DEEP-SEA ANCHORING AND MOORING 



John D. Isaacs 



1. Introduction 



The following relates to mooring light devices in the deep ocean at depths 

 from 100 to 3000 fathoms, and is intended as an introduction to those planning 

 research approaches. For those who plan to design and install such deep-sea 

 moorings, a more elaborate treatment is available (Isaacs et al., 1962). 



This discussion is based on about eight years of deep-mooring experience at 

 the Scripps Institution of Oceanography from which, at times, as many as 

 thirty stations have been moored and maintained in large deep-sea areas. 



2. Historical Background 



The history of deep moorings dates back at least as far as 1888-1889 when 

 the U.S. Coast and Geodetic Survey Steamer Blake, under the command of J. 

 E. Pillsbury, carried out studies of the Gulf Stream. During these investigations 

 the Blake was anchored at several locations in depths to 4000 m. Subsequently, 

 other vessels were anchored in great depths in the North Atlantic and else- 

 where. Some vessels, including the Meteor, have been anchored in depths 

 greater than 4500 m for periods up to two weeks, and the Meteor was anchored 

 in 5500 m for two days. Although most of these efforts employed anchors 

 weighing 400 to 500 lb, the E. W. Scripps was anchored successfully in depths 

 of about 1600 m using a Danforth anchor of only 40 lb. 



Scopes (length of mooring rope : depth of sea) of 1.1 to 1.6 have been used in 

 the open sea and scopes of 2 to 3 have been used in anchoring in the strong 

 currents of the Gulf Stream. 



In recent years, a somewhat newer type of mooring has been introduced. 

 This is a "taut-mooring" developed at Scripps and described by Bascom (1953). 



Fig. 1 shows a more recent mooring of this type, designed by J. D. Isaacs, 

 R. P. Huffer and L. W. Kidd, that is adapted for use in any depth of water. 



Referring to Fig. 1, the station consists of (1) a dead weight on the bottom ; 

 (2) a mooring wire of high strength steel ; (3) a special float that provides high 

 tension in the line and which is submerged 15 to 100 fm below the surface; 

 and (4) a buoyant pennant connecting to the surface buoy, a skiff, which contains 

 the recorders. 



An equally satisfactory type of mooring with rather different applications 

 has been developed and used by Allyn Vine of Woods Hole Oceanographic 

 Institution (in litt.). This is shown in Fig. 2, which is self-explanatory. The 

 essential feature of this mooring system is the buoyant fiber rope of which the 

 lower half of the mooring cable is composed. This eliminates the need for a 

 submerged buoy. Where the instrumentation is principally for observations on 

 the surface, and where close station-keeping is not important, this type of 

 mooring has the advantages of simplicity and ease of installation. 



A third type of mooring is the free-moored instrument without a surface float. 



[MS received October, 1960] 516 



