Laboratory test and field evaluation of double armored electro-optical cable for the JAMSTEC/Deep Tow

The JAMSTEC/Deep Tow system was developed in 1992 and has a depth capability of 6500 m. In order to get color video images in real time, fiber-optic cable was indispensable instead of coaxial cable. After several tests and evaluation, an 8 km long electro-optical cable, which comprised of four electrical conductors and four single mode optical fibers, was manufactured in 1991. During the initial sea trials in 1992, the cable end was severely damaged by kinking at Sea State 4. The electro-optical cable was superior in elongation and torque balance to the coaxial cable. The kinks occurred by accumulating residual torque at the cable end, which was caused mainly by insufficient pre-tension in the factory. It was found that residual torque was apt to propagate toward the cable end with well torque balanced cable (armored electro-optical cable) rather than unbalanced armored cable such as coaxial cable. Practically, high rigidity is more important than good torque balance of the cable.