Mechanical engineering challenges in the development of deepwater ROV (ROSUB 6000)

A deep water work class ROV (ROSUB 6000) rated for 6000 m subsea depth has been developed at National Institute of Ocean technology, Chennai, India. ROSUB 6000 system consists of a free swimming ROV, tether management system (TMS), power container, control console container, Launching and retrieval system (LARS) and electro optical umbilical cable. Developmental work of ROSUB 6000 system started from March 2003. During the developmental phase and several depth qualification sea trials various kinds of mechanical engineering challenges were encountered. This paper enumerates the challenges encountered. Water entry is one of the major challenges in subsea systems. Water entry through pressure housings may be catastrophic, since pressure housings carries control electronics. Control electronics switches off when water entry alarm is given stopping all the ROV operations. Water entry in the pressure cases of ROV has happened several times. Each instance the reason behind the water entry was different. Failure of components like torque arrester in TMS deep sea winch and thruster frames were analyzed and suitable methodologies to avoid these failures are brought into the practice. Challenges in deck handling of ROV and TMS are weather conditions and tether twist during initial attachment of ROV with TMS. One another big challenge is the launching and retrieval of the system. Challenges due to rough seas, launching and retrieval system hydraulic system faults, operational human errors and their effects on the system components are recorded and reviewed to improve the system reliability. The importance of buoyancy corrections and hydraulic system maintenance were learnt during the various phases of lab and field testing of the deep water ROV.