Docking at the Chennai harbour for less than a week before embarking on its next voyage to the Central Indian Ocean Basin, Oceanographic Research Vessel, Sagar Nidhi is the pride of the National Institute of Ocean Technology (NIOT), Chennai. Commissioned for research in 2008, Sagar Nidhi helps NIOT in technology demonstration work on deep-sea mining and tsunami studies.

An ice class vessel, it can cut through thin ice of 40 cm depth, which helped in its last voyage up to the southern seas (69 degrees South) and is the first Indian vessel to have gone to Antarctic waters. The ship is the first of its kind in the country and has been used several times for launching and retrieval of remotely operable vehicle (ROV) and the nodule mining system, said Dr. M.A. Atmanand, Director of NIOT.

The most fascinating aspect is the ship’s dynamic positioning system (DPS) which keeps the ship in a fixed position at mid- sea. The DPS is a computer-controlled system which automatically maintains the position of the ship at mid-sea. It uses propellers, thrusters, and several sensors — position reference sensors, wind sensors, motion sensors — and gyrocompasses which provide information about the environmental forces acting on the ship. A global positioning system (GPS) picks up the ship’s position from a set of satellites and this is interfaced with the DPS and controlled using a master control. Based on the inputs from these, the system sends a signal to the thrusters and propellers to position the system as per directions from the master control.

With the DPS, even at sea-state 5 — when the wave height is 4–5 metres — the ship’s position can be fixed to within a variation of less than 50 metres. The wave height can go up to 10 metres, but scientific operations are normally not performed above sea-state 5. Often, the weather does not change so quickly, but if it does, operations may be halted if the aberrations are severe enough.

Ships that do not have a DPS can be manoeuvred only manually so that the position of the ship is fixed up to deviations of 200-300 metres. This feature comes in useful when deploying remotely operable vehicles, Tsunami alert systems etc, which require the ship to maintain a fixed position for a very long time. Sagar Nidhi’s DPS system often is put to work for 3-4 days at a stretch.

The NIOT scientists’ work on concepts to improve the reliability of the Dynamic Positioning System has won them the National Maritime Award for Technological Innovation, says Dr. Rajasekhar, Head of Vessel Management Cell, NIOT.

The cost of this DPS is about Rs.50-60 crores. There are perhaps 25–30 other ships in the world which have this good a DPS.

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