Missing of the ROV Kaiko vehicle - problem on the secondary cable

Kaiko has been the only full ocean depth survey system in the world since 1995. The Kaiko system comprises a launcher, the vehicle, primary cable, secondary cable, on board equipment and the R/V Kairei as a mother ship. In May 2003, the secondary cable of the Kaiko snapped during the 296th dive at a depth of 4675 m in the Nankai Trough, 130 km southeast off Cape Muroto on Shikoku Island, and the vehicle has been missing. The secondary cable of the Kaiko is an electro-optical cable, and its tension member is made of aramid fiber. It was found that the secondary cable snapped against a tension less than 400 kgf, which was far below the designed breaking strength of 3 tonf. The aramid tension members were investigated and found to have weakened by bending under extremely high hydrostatic pressure, and local fatigue of the tension members occurred at the cable termination near the vehicle.