Visby Design
The Visby corvettes are designed to handle all types of naval mission, including mine clearance, antisubmarine warfare (ASW), surface combat, marine surveillance and the protection of commercial shipping. The Visby corvettes are designed for inclusion in the new rapid-reaction force. Their stealth technology makes them difficult to detect with radar and other advanced forms of detection. Everything can be seen and heard from the bridge, while the vessel itself remains undetected, offering multiple tactical benefits. The vessel can also de-activate its stealth mode, if it wishes to demonstrate its presence, and then reactivate to 'vanish' again. The Swedish Navy has always operated in the littoral and is highly specialized in the necessary techniques. Of course, there are many littoral zones across the globe, through which exports and imports must be shipped from and to the world's large and growing ports. In a post 9/11 world, this is precisely where the threat lies. A well-planned terror attack could have devastating consequences.
The Visby is designed to minimize all signatures - optical and infrared signature, above water acoustic and hydroacoustic signature, underwater electrical potential and magnetic signature, pressure signature, radar cross section and actively emitted signals. The difference in detection range between an ordinary vessel and Visby creates a considerable zone where the Visby can see but not be seen.
It had an unusual architecture of flat panels with wide angles of slope with the application of radar absorbent constructional materials (composite plastic), which was necessary to decrease the thermal and infrared signature on several points. The weapon was completely stowed away flush inside the bulkheads and the hull, which was necessary again to meet low-signature requirements, even the turret installed outside the artillery mount had a low-signature design made of radar absorbent materials fitted with a retractable gun tube. The mooring equipment and aerial posts have the same layout, — the features which usually increase the electron paramagnetic resonance (EPR).
The hull is designed on stealth principles with large flat angled surfaces. Every feature that need not necessarily be located outside the hull has been built in or concealed under specially designed hatches. The gas turbine exhausts have been concealed in hidden outlets close to the water surface at the stern of the vessel.
The vessel is built of sandwich-construction carbon fibre reinforced plastic (CFRP). The material provides high strength and rigidity, low weight, good shock resistance, low radar signature and low magnetic signature. The material dramatically reduces the structural weight (typically 50% of a conventional steel hull). This results in a higher payload carrying capability, higher speed or longer range.
The vessels have been equipped to be able to cooperate with other parts of the Armed Forces that occur in the maritime area, such as the air force, coast guard, civil protection, customs, police and civilian shipping. The Visby corvettes will also be able to behave in particular as a good management of resources for long-term efforts at sea. All missions are supported by CETRIS - the real-time command, control, communication, intelligence and interoperability system (C4I2). The system is modular and open, and allows for integration of future technologies, without expensive changes.
The Visby is designed for the installation of a surface-to-surface missile (SSM) system. On the Swedish version, eight SSM (RBS15 MkII) can be fully integrated into the hull and covered with smart rapid hatches. The MCM system consists of a combination of extremely low signatures, sensors and weapons, and very high shock resistance. For detecting and classifying mines, the Visby uses ROVs (remotely operated vehicles). A powerful sonar system is used to detect, locate, classify and supply real-time target data to the weapons. In addition, the sonar-equipped ROV-S can be launched for surveillance and classification of targets. The Visby is equipped with wire-guided, homing 40 cm torpedoes. A submarine can also be attacked with an ROV-E or the brand-new 5" ASW multiple rocket system.
The Visby is equipped with a combined diesel or gas (CODOG) turbine arrangement for high speeds and two diesel engines for low-speed. The engines are connected to two gearboxes, driving two waterjet propulsors. The engines provide a maximum speed of 15 knots for long duration and 35 knots for short duration. The ship has bowthrusters for harbour manoeuvring.
The 600 ton Visbys are multi-role vessels including mine warfare, anti-submarine warfare, surface warfare, maritime surveillance and maritime security. However, and they are not able to strike-down helicopters in a hanger as planned. Tests had shown that the ships can operate a lightweight (2-3 ton take-off weight) helicopter such as the Agusta Westland A-109M helicopter (Swedish designation HKP 15), for limited periods, lashed to the helicopter platform, although this compromises the ship radar and heat signatures. The helicopters are part of the Visby's anti-submarine capability using a sonobuoy transmission and processing system acquired from the Spanish company SAES, which is now supplying the ships with the SDL-SS relay and sonobuoy processing systems that receives acoustic data from sonobuoys launched from the ship itself and includes a ship-ship link as well as satellite communication capabilities.
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