Theoretical study on rotation of doubly layered torque balance cable

Remotely Operated Vehicle (ROV) uses long tether cable for power supply and signal communication between a ROV and its support vessel. However there have been many accidents on this tether cable, such as kink and disconnection caused by rotation of the cable. The tether cable is usually a torque balance type one with its strength members of inner/outer layer braided reverse direction each other. However, even if a torque balance of the cable is perfect, cable rotation occurs in most ROVs while paying in/out of a tether cable into the ocean. In this research, calculation method of strand track of a tether cable bent on a sheave was established, and the reason of the cable rotation was found to be the change of track length caused by bending of the tether cable on sheave, applying this calculation method. Comparison of the calculated results and measured data of JAMSTEC ROVs shows this calculation method to be very good to explain the rotation phenomena.