Jet-powered warship, built in KolkataWater Jet Fast Attack Craft

Kolkata: Think ship and one of the things that come to mind are propellors. On Thursday, the warship launched by Garden Reach Shipbuilders and Engineers (GRSE) at its Rajabagan dockyard has none. No, this wasn't an oversight. Fast Attack Craft (FAC) INS Tarasa is a kind of ship that doesn't need propellors. She uses an advanced technology called 'water-jet propulsion' that has several advantages over conventional propellors.

The 48-metre long, 7.5-metre wide ship has a displacement of 315 tonnes and can achieve speeds of over 35 knots. At lower speeds (12-14 knots), the FAC can cover a distance of 2,000 nautical miles without refuelling.

INS Tarasa, which was launched by Aruna Korde, wife of vice-admiral Jaywant Korde, controller of logistics, Indian Navy, is fitted with three water-jet propulsion systems powered by marine diesel engines, each of which can generate 2,720 KW of power. During fitting out, it will get an indigenous CRN-91 30mm gun.

"The ship will be handed over to the Navy after being fitted out and completion of sea trials. The INS Tarasa is an improved version of the FACs built by GRSE for the Navy in the past. She has an efficient hull form developed by the in-house design centre at GRSE and proved through extensive model testing. The hull form of this class of ships have excellent sea keeping characteristics and manoeuvrability. They are cost-effective, fuel-efficient, powerful and well suited for attack missions as well as other patrolling, anti-smuggling, anti-poaching and rescue operations carried out by the Navy. GRSE is on a growth path and we are committed to supply more advanced ships to the Navy and Coast Guard," said rear admiral (retd) A K Verma, chairman-cum-managing director, GRSE.

A jet propulsion system is similar to that of a water pump. It generates a propulsive force or thrust from the reaction generated by forcing out a stream of water through the rear end of the ship. Water jet units are mounted in the aft section of the ship's hull. Water enters the unit through an intake grid at the bottom of the ship and gets drawn through the inlet duct by the impeller which also increases the pressure or "head" of the water flow.

This high pressure water flow is then discharged through a nozzle as a high velocity jet stream. The discharge of this high velocity water jet generates a reaction in the opposite direction that is transferred to the ship's hull, propelling it forward. To make a ship move in reverse, the direction of the water jet is also reversed.

"This technology has several advantages. It provides precise steering control at all speeds and sideways movement of the vessel. It also provides high-efficiency astern thrust, making it possible to crash stop the ship, even at high speeds. There is less hull resistance as there are no underwater appendages like propellors. Ships using this system can operate in shallower draught and require less maintenance," a senior official said.