Maareech in the Indian Navy
Those familiar with the famous Indian legend of ‘Ramayana’ would know about ‘Maareecha’, the rakshasa who transformed to a deer thereby enabling Ravana to abduct Sita. You see, ‘Maareecha’ was a decoy or an illusion. And it is quite fascinating of DRDO to come up with the right name ‘maareech’ for the Advanced Torpedo Defence System (ATDS). ‘Maareech’ was inducted into the Indian Navy in June 2020.
It provides a reliable defence mechanism against possible attacks by both vintage and modern torpedoes. This system is a detection plus countermeasures system. It can shield the vessel against multiple launches at the same target.
Recently an expression of Interest (EOI) with regard to Transfer of Technology (ToT) of Maareech ATDS has been released. The EOI is for Indian manufacturers with sufficient experience, expertise and willingness to undertake the role of Lead System Integrator (LSI). The LSI will serve as a single point of contact (SPOC) between NPOL, Kochi and the Indian Navy.
The beauty of Maareech is that it has the capability to automatically detect, track, alert and decoy the incoming acoustic homing torpedoes. Maareech as a system comprises of the following sub-systems:
- Hull Mounted SONAR
- Towed Array of SONAR and decoys
- Expendable decoys
- Tow cable
- Hydraulic Winch
- On-board electronics
- Software package
Hull Mounted SONAR
The conventional hull mounted SONAR forms a part of this system.
This sub-system comprises of various modules in a linear manner interconnected by underwater connectors. Each module has hydrophones array spaced as per frequency range called as the towed receiver array. Each module has ‘L/R ambiguity array’ capable of detecting and resolving the ambiguity of whether the torpedo is to the left or right. These modules have a ‘Towed decoy sub-module’ and a Fiber Optic conversion module (FOM) for telemetry.
The towed array modules have typical diameter of 78 mm and a cumulative length of 40 m. Their components are housed inside a flexible polyurethane hose. This hose is filled with a fluid. It is most likely to balance hydrodynamic pressure as well as to adjust buoyancy based on depth of operation. These modules are interconnected using electro mechanical connectors. This sub-system being in water is a part of the wet end sub-system.
The ship-borne expendable decoy system consists of a decoy launcher, an FCS and expendable decoys. There are 40 ship borne expendable decoys and these would be used first unless the worst case scenario of using the towed decoys becomes a necessity.
The towing cables are electro-optic mechanical cables. The electrical lines within are for powering the array whereas the fiber optic lines are for seamless data telemetry link between the array and onboard systems. These cables have strength members and steel armour to withstand hydrodynamic loads experienced when towing. The cable is extended through a winch system at the ship stern.
The steel armour and strength members facilitate load transfer to the winch system. The typical length of the tow cable is 500 m. Hence there is a sufficiently good range for adjusting the depth of operation. The advantage of such large length is to keep the vessel well clear off the torpedo impact range. The Tow cable is terminated to FOM at the towed array end and Winch rotor box at the winch end. The Tow cable forms a part of the wet end sub-system.
The hydraulic winch is for winding, unwinding and stowage of the array and cables. The entire winch system is designed for stowage of 500 m of tow cable and the towed array. The spooler system has auto and manual modes. It has adjustable arrangements for passage of tow cable and towed array. It can be engaged or disengaged easily.
The winch can be electrically operated during emergency. The operations of the winch are monitored and controlled through a winch Master control console right beside it. It has a Control Valve desk for hydraulic operation. The optic signals from the cable are converted to electrical signals through the opto-electrical conversion module.
The electrical slip ring helps in making the electrical connection from the control module to the winch. The Winch is equipped with a load sensing unit. This helps in quantifying the towing load on the winch and determines the torque of operation. Upto 8000kgf of line pull could be withstood by the winch whereas the maximum RPM is 18 RPM. The fairlead assembly helps in guiding the cable and prevents its lateral movement over the winch. This entire system has various interlocks and safety features to facilitate remote operation from SONAR room.
The data from the array sent via the fiber optic data link is processed by the OBE sub-system. Display cum processor cabinet houses the processing electronics and displays. The displays have multiple pages which can be changed based on operator’s requirements. It presents the sonar information in twin displays using state-of-the-art (HMI) Human Machine Interface schemes. It has Keyboard and Trackball interfaces. The OBE provides interfaces with the existing Hull mounted arrays as well.
The power supply for the OBE is adapted for ship supply through Automatic Changeover Switch and Isolation Transformer. Distribution of power supply and signals are done through various junction boxes fitted at different locations of the platform. The Hull mounted array Interface cabinet (HMA) extracts pre-amplified sensor data and converts it to Ethernet format for further processing at Display cum processor cabinet. The Ethernet links are used for Data and Control telemetry.
The SONAR data is recorded using the Digital Data Recorders (DDRs). It can replay pre-recorded data and even plug-in test data to the OBE for evaluation and training. The data from the OBE is interfaced with Fire Control System (FCS). This facilitates seamless triggering of expendable countermeasures. The motion of incoming torpedo is predicted using the Contact Motion Algorithm.
The system software resides on the on-board hardware modules. It implements advanced signal processing algorithms for torpedo detection classification and countermeasures in both active and passive mode.
How Maareech works
- The ship’s hull mounted SONAR gets an initial track of the incoming torpedo.
- The signal received by hull mounted SONAR is converted to optical signal and transmitted to the winch Master control.
- The electrical slip ring makes the electrical connection and the winch is then extended.
- The towed array of SONAR and decoys is submerged. The towed array then tracks the torpedo. It tracks the speed, direction and depth. It paints a track with an expected time and position of impact.
- The signals are converted to optical signals using the Fiber Optic Conversion Module. Then the optical signals are transmitted through the Fiber Optic lines to the display cum Processor cabinet of the OBE.
- The OBE being interfaced with FCS calculates the firing solutions. By using contact motion analysis, it comes up with recommendations for the CO to execute a decoy launch and navigate the course away from incoming torpedo.
- The decoy once launched overloads the seeker head of the incoming torpedo with a powerful acoustic signature.
- The incoming torpedo therefore treats the decoy like a much larger target and alters course away from the ship.
Use by Indian Navy
11 Indian Navy surface ships will be equipped with this complete home-made ASW suite. The rest ships will be equipped with only the dry end i.e without the towed array. One of the biggest concerns of the Indian Navy got cleared out thanks to this system from DRDO.
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