518 ISAACS [CHAP. 24 



recording period of from a few hours to a few days. The instruments rise to the 

 surface at a pre-set time and are recovered. One such mooring is described by 

 Isaacs and Schick (1960) and its essentials are shown in Fig. 3. The ordinary 



,Recovery spar 



, Additional floatation 



Fig. 3. Free instrument vehicle and mooring. 



pay-load is about 25 lb, but additional loads in increments of 75 to 100 lb are 

 obtainable by adding further buoyancy in the form of rubber drums of gasoline 

 or diesel oil. 



3. Problems of Taut-Mooring 



The remainder of this discussion is concerned almost entirely with the taut- 

 mooring, for the reason that such moorings provide great potential for deep-sea 

 measurements and yet require the greatest discretion in their design and use. 



The primary intent of deep-sea mooring is to maintain a surface float in some 

 geographical position with the simplest effective system. 



The forces of relatively steady magnitude that tend to displace the system 

 are primarily the horizontal drag forces imposed on the components by wind 

 and current. These are principally applied near the surface. 



Intermittent impulsive or oscillating forces, both horizontal and vertical, 

 are imposed by the waves, and these forces dictate many of the design charac- 

 teristics of the system. The initial force available to the designer for resisting 

 the displacement of the system is almost solely shear force on the bottom 

 material (although other possibilities exist). 



The problem thus is to conduct the horizontal drag forces, principally near 

 the surface, some miles vertically so that they are resisted by the bottom shears, 



