INTRODUCTION 



A kinked cable can jeopardize the performance of an undersea cable 

 system, which may contain valuable data and hardware. Repair of such 

 systems is costly and difficult (if not impossible in some cases). 

 Therefore, the cable components in such systems must be properly designed 

 to assure kink-free operation. Simulation of cable performance by use of 

 mathematical models can prove a valuable designing tool. Rotational 

 behavior and likelihood of kinking of a cable before its fabrication can 

 be predicted. 



After a cable is constructed, data on potential rotation and kink 

 formation are needed to develop proper procedures for handling the cable 

 during ship loading and deployment. 



In addition, it may be feasible to replace cable testing by 

 analytical predictions and thereby save cost and time. 



A kink in a wire rope or a metallic electromechanical cable may be 

 defined as a tight twist or curl resulting from rotation about the cable 

 axis. Usually, a kink will cause electrical failure or mechanical 

 damage or both. Preventing the formation of such undesirable deformations 

 is essential for successful cable deployment. 



Although the mechanism of kink formation in complex cables is not 

 fully understood, an appreciation of the kinking problem can be obtained 

 from a simple demonstration with a rubber band. Fix one end of a rubber 

 band and twist the other end until a kink is formed. Then apply some 

 tension and observe the kink being pulled out. Twist the rubber band 

 more and a kink will form again. This simple demonstration shows that a 

 kink will form at a critical twist or torque corresponding to a particular 

 value of tension. A wire rope or cable is an elastic body, and it is 

 reasonable to assume that there also exists a critical tension or a 

 critical torque for kinking as with the rubber band. The main difference 

 between a cable and a rubber band is the complex wire structure in the 

 cable compared with the homogeneous rubber material. 



Torque is needed to form a kink. Where does the torque come from? 

 The history of loading on the cable determines the amount of residual 

 torque. For example, when a payload is being lowered into the ocean, 

 end rotation may occur due to the weight of the payload or the payload 

 hydrodynamic movement. Torque at this time is zero until the payload 

 reaches the seafloor where the tension suddenly is reduced to zero. 

 Now, the rotation which occurred converts to end torque. Kinks form to 

 release this end torque. Therefore, for kink-free operation, torque- 

 balanced cable and slow lowering speeds are essential. However, this 

 rule of thumb is not adequate for operations requiring high reliability. 

 The criterion for cable kinking must be established and acceptable external 

 loadings specified to assure safe operation. 



