Cable Rotational Properties . Because a cable is constructed with 

 helically-wound preformed wires, it rotates not onlv under externally 

 applied torsion but also under tension. The resistance to such loadings 

 varies, depending on the size, material and mechanical design of the 

 cable. The amount of torque-induced rotation is a measure of the tor- 

 sional stiffness, which is an important factor affecting the formation 

 of kinks in a slack cable. Cables having small torsional stiffness tend 

 to twist under torque and are easy to handle during coiling. Cables 

 with large torsional stiffness have high resistance to rotation and 

 would rather deform into a loop than rotate about its longitudinal axis. 

 Another characteristic of stiff cables is the ability to sDread torque 

 throughout its length, even when in coils. This redistribution of torque 

 within the tank may be responsible for the formation of kinks when the 

 cable is payed out. 



During deployment, the controlling factor is the tension-induced 

 rotation. Cable rotation occurs when the cable and payload are suspended 

 freely in the water. When the payload lands on the seafloor, slack occurs 

 in the cable. This reduction in tension causes the cable to untwist. 

 However, since both ends of the cable are now unable to rotate, the cable 

 deforms and twists into loops. As tension is reapplied, the twisted 

 loops form kinks. Because a slack line is necessarv to form these twisted 

 loops, maintaining a small cable tension (about equal to the weight of 

 the wire) is essential to prevent kink formation. Another method of 

 avoiding kink formation is to use twist-free cable. To provide satis- 

 factory results, the cable should be designed so that it will not rotate 

 under the expected range of tensions. 



There are three types of cables that can be considered to be nearly 

 twist free. The first is a double-armored cable designed so that the two 

 layers of armor produce an equal but opposite torque under a selected 

 working tension. The second type has a central strength cable which is 

 a torque-balanced wire rope. The torque produced by each individual strand 

 is balanced by the torque produced bv the lay of the rnne. The last type 

 of design uses the same principle of torque-balanced wire rope, but the 

 torque-balancing strands are now laid outside the electrical core as 

 armor. Some manufacturers advertise cables that rotate only 0.1 degree 

 per foot at 50 percent of the breaking strength. While toraue compensa- 

 tion is advantageous during cable deployment, the contrary is true during 

 shipping and loading. Such cable is difficult to handle during coiling 

 and uncoiling in a tank. 



Equipment and Hardware 



Cable Storage Equipment . A special feature of the cable tank is its 

 large volume; for example, the largest tank on C/P LONG LINES can store 

 2,000 nautical miles of 1 1/4-inch-diameter deep-sea armorless cable. 

 The minimum coil diameter is 10 feet. For each coil of cable in the tank, 

 a rotation of 360 degrees about the longitudinal axis is added to the 

 cable. The tank is effective for long lengths of armorless transoceanic 

 telephone cable (SD type) because the cable has a small central strength 

 member which provides little resistance to rotation. The cable packs 

 nicely in the tank without kinks. As the cable is payed out from the 



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