Reliability Assessment and System Performance Improvement of ORV Sagar Nidhi Propulsion System

Diesel-electric propulsion system offers many advantages to research ships, viz. economical, environment friendly, reliable, ease of operation and control, optimal manoeuvering and positioning, low vibration and noise levels. ORV Sagar Nidhi is equipped with diesel electric propulsion. The propulsion power is provided by azimuth thrusters which are driven by frequency controlled AC motors. The ship has dynamic positioning system for station keeping and better manoeuvering. During a scientific cruise, starboard azimuth thruster motor tripped due to zero resistance in winding, thereby reducing the propulsion power. Because there is no redundant motor available, vessel completed the voyage with single thruster. As a result of motor failure, propulsive power of the vessel was reduced drastically and the voyage plan had to be altered to match the ship schedule which resulted in skipping many sampling stations. In this article, the possible cause of thruster motor failure was analysed and remedial action was taken to rectify the same. This article also provides different solutions to improve the reliability of propulsion system and minimizing the downtime of vessel.