INS Alleppey, one of the six Ponchicherry class coastal minesweepers purchased from the erstwhile USSR in the 1970s, was on Friday decommissioned at sunset after nearly 35 years of service under the Western Naval Command. The vessel was home ported in Mumbai and is the last of the Pondicherry-class vessels.
- The Indian Navy had acquired a total of 12 boats from Russian — originally the Natya-class — between 1978 to 1988 in batches of six with the latter batch called as the Karwar class.
- The previous five vessels, INS Pondicherry, INS Porbandar, INS Bedi, INS Bhavnagar, and INS Ratnagiri were decommissioned between 2007 and 2012.
- Six of the Karwar class boats, including the INS Karwar, INS Cannannore, INS Cuddalore, INS Kakinada, INS Kozhikode and INS Konkan are meanwhile based at Vishakhapatnam with the Eastern Naval Command (ENC).
Function of Minesweeper vessel:
The function of the vessels is to clear civilian ports of sea mines airdropped or planted by opposing navies. Large and heavily armed, the boats are constructed out of U3 low magnetic steel so as not attract the sea mines themselves.
What are naval mines?
- A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines.
- These mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel.
- These naval mines were extensively used during second World War.
- Earlier Contact mines, moored contact mines were used, where these mines need to be touched by the target before they detonate.
- Now a days, advanced Influence mines are used, where these mines are incorporated with various sensors such as magnetic, passive acoustic or water pressure displacement caused by the proximity of a vessel. They detect the presence of a vessel and detonate when it comes within the blast range of the warhead.
How do Minesweepers work?
A sweep is either a contact sweep, a wire dragged through the water by one or two ships to cut the mooring wire of floating mines, or a distance sweep that mimics a ship to detonate the mines. This method was useful in case of contact mines or moored contact mines. Please see following picture.
Since now a days, influence mines are used, the minesweeper are designed to reduce the chances of it detonating mines itself; it is soundproofed to reduce its acoustic signature (acoustic signature is made up of Machinery noise, noise made by ship’s propeller and noise generated by the movement of water displaced by the hull of a moving vessel.) and often constructed using wood, fiberglass or non-ferrous metal, or is degaussed ( by installing electromagnetic coils into the ships and also helps the bias field to be reversed.) to reduce its magnetic signature.
After a failed bid by the previous UPA government in 2011 to procure Mine Counter Measure Vehicles (MCMV) as Kangnam Corporation — the South Korean company selected for its lowest bid — was found to have violated transparency procedures.
Current defence minister Manohar Parrikar asked the government-owned Goa Shipyard Limited to construct the vessels.