(3) Use more than one cable. However, it should be borne in mind 

 that each cable must actually be designed to withstand much more than an equal 

 share of the total load because of some adverse conditions that can readily oc- 

 cur. Also, the cables can be tangled, a situation which can lead to serious 

 problems. 



B. CONCLUSIONS AND RECOMMENDATIONS 



The static stresses due to the weight of the array and cable can be 

 taken care of by practicable cables . For a maximum depth of 20, 000 feet and 

 50- and 100-ton steel arrays, the maximum static stress in a steel cable of 

 three square inches metallic area is 100,000 and 130,000 psi, respectively, 

 when no buoyancy is introduced anywhere. For the same depth and a 15-ton 

 aluminum array (which in water weighs about 10 tons), the maximum static 

 stress in a steel cable of one square inch metallic area is 100, 000 psi. The 

 ultimate tensile strength of such cables is about 220,000 psi; therefore, these 

 cables can handle these stresses with a factor of safety of about two. However, 

 the above static stresses must be reduced, because higher factors of safety 

 (about 3) are usually required for such an operation, and in addition, there are 

 other stresses (d3niamic) in the cable. 



Static stresses can be reduced by increasing the metallic area of the 

 cable or by making the array and cable more buoyant. Since a large portion 

 of the static loading is due to the weight of the cable (the maximum length of 

 cable which can hold itself without any factor of safety is only 62, 000 ft), the 

 most effective method is to introduce buoyancy in the cable. An equivalent 

 way of effecting this is by using a tapered cable. 



Nylon type ropes are desirable in this respect, because they are 

 much lighter than steel ropes while their ultimate strength is just about as high 

 as that of the strongest steel ropes. The velocity of sound of nylon ropes is 

 also much smaller than that of steel ropes. With respect to the dynamic stres- 

 ses that can be induced by a rough sea, these two factors (small weight and 

 velocity of sound) render nylon ropes undesirable. Of course, the small modu- 

 lus of elasticity, characteristic of nylon ropes, is a favorable factor and can 

 probably compensate for the undesirable effects of the above two factors. In 

 any case, in this operation there are some environmental hazards which make 

 steel ropes preferable to nylon ropes . 



The effects (stress and array offset) of reasonable ocean currents 

 are negligible, provided that the vertical forces due to gravity minus buoyancy 

 are much larger than the horizontal drag forces due to the currents . This will 

 be the case in practice, because buoyancy must not be used to the extent of 



:artl)ur Sl.littlcJnc-. 



S-7001-0307 



