While some states are using only some technical solutions or are preparing to build full-fledged stealth ships, Sweden is already using several corvettes, designed with a view to reducing visibility to the maximum. Cornets of the Visby project ("Visby") are few - only five such ships have been built. Nevertheless, they combine a number of original measures that allow solving a number of combat missions with minimal risk of being detected.
The development of the Visby project was preceded by experiments designed to study stealth technologies and their prospects in the military shipbuilding business. At the end of the eighties, the Swedish industry built a Smyge skeg-type hovercraft. A small ship (full displacement of about 140 tons) allowed to determine the future of several new technologies, as well as to work out some elements of the appearance of promising warships. A large number of developments obtained during the Smyge project were later used in the Visby project.
In the early nineties, the Swedish Defense Ministry was going to create two ship projects at once: YSS (Ytstridsfartyg Större - “Big Warship”) and YSM (Ytstridsfartyg Mindre - “Small Warship”). However, shortly after the start of work, the projects were combined in order to save. Further work was carried out by Kockums in the framework of the YS2000 project (Ytstridsfartyg 2000 “2000's warship”). Later, the project received a new name corresponding to the name of the lead ship - Visby. Due to the merger of the two projects, the YS2000 ships had to perform a wide range of tasks: from the search for submarines and the attack of surface targets to the setting of minefields and patrol service.
The YS2000 / Visby project was completed in the mid-nineties. It used a number of new technologies, not only for Swedish, but also for world shipbuilding. In February, 1996, the laying of the lead ship, named Visby, took place. The ship was launched in the 2000 year and was on trial until 2005. Five new corvettes were laid from 1997 to 1999 year, however the construction of the last of them (Uddevalla) was soon canceled. In 2009, the second and third ships of the Helsingborg and Härnösand project were accepted into the Swedish Navy. Two newer corvettes, Nyköping and Karlstad, are still being tested.
Employees of the company Kockums managed to create the first in the world combat ship, fully using stealth technology. The corvette turned out to be relatively small: the total length of the 72 meter, the maximum width - 10,4 m, the draft - about 2,4 m. Thanks to the use of new technologies, the Swedish shipbuilders were able to reduce the weight of the structure. The full displacement of the lead ship Visby does not exceed 640 tons.
The main factor that made it possible to reduce the weight of the structure was the original composite material from which a number of important parts of the structure were made. As a base material for the manufacture of the hull and superstructure, a set of polymers reinforced with carbon fiber and vinyl was chosen. In the course of long-term studies, Swedish specialists managed to find a suitable composite for use, providing a light weight of the structure (twice as light as a similar structure made of metal), high rigidity and impact resistance. At the same time, one of the main reasons for using a composite material was its low reflectivity. The frame of the ship was assembled from metal parts.
The hull and superstructure of the Visby corvette are made in the form of a monoblock: the surface part of the hull smoothly passes into the superstructure without unnecessary details that can increase the visibility of the ship. The surface of the ship is a combination of mating flat panels of various shapes. The contours of the underwater part are made “traditional” because they do not affect the visibility for radar systems. A casing is provided on the tank of the ship, covering the artillery from radiation from the radar. In the middle part of the body is placed superstructure of characteristic shape. On the roof of the superstructure there is an antenna mast, covered with a radio transparent cover. The stern of the hull is reserved for a landing site about 20 meters long. All weapons systems as well as mooring equipment are placed inside the hull or superstructure and are covered with shields made of the same materials as the hull.
The internal volume of the hull of the Visby project ships is divided into eight compartments with watertight bulkheads. Cabins and cockpits of the crew, sanitary facilities, as well as a nasal diesel generator, hydroacoustic station and thruster are located in the three bow compartments. On the different decks in the fourth compartment there are a mess-room and a dining room, a galley with a storeroom, as well as the main command post. It is noteworthy that the premises of the officers' cabin are also used as an infirmary. In the volumes of the fifth compartment are various weapons systems and auxiliary equipment. In addition, in the fifth compartment is the control post of the main power plant and a tank for aviation fuel. In the hold from the sixth to the eighth compartments various equipment of the main power plant is located. The upper deck is reserved for torpedo tubes and the volume for the necessary armament. If necessary, a helicopter hangar can be equipped in the stern of the ship.
The main power plant of the Corvettes of the Visby project is made according to the CODOG system and uses several types of engines. In the sixth compartment there are two diesel engines MTU 16V 2000 N90 with a capacity of about 1770 hp. each. To reduce noise, the engines are mounted on damping devices. Diesel engines are used when driving at economical speeds on the order of 15 knots. To accelerate to maximum speed, the ship can use four Vericor TF50A gas-turbine engines with a total power of 16000 kW (approximately 21750 hp) installed in the aft compartments. With maximum engine power, the Visby Corvette can accelerate to 35 nodes. Sailing range - up to 2500 miles.
The torque of the engines through the gearbox is transmitted to the two jet propulsion KaMeWa 125 SII. At a speed of 15 knots, the water jet provides about twice the noise level compared to traditional propellers. Water jet helps to reduce the acoustic visibility of the ship. In addition, measures have been taken that reduce the visibility of the corvette in the infrared range. The exhaust gases of all six engines are discharged through a pipe in the stern of the ship, located as close as possible to the water.
The maneuverability of the ship is provided by swiveling nozzles of water cannons, as well as two rudders mounted behind them. The latter allow you to maneuver with greater efficiency at low speeds. In addition, a bow thruster HRP 200-65 is provided in the nose section of the Visby corvettes.
All five Visby corvettes initially had a common set of radio-electronic equipment. The three-coordinate radar station Ericsson Sea Giraffe AMB is used as the primary means of target detection. The characteristics of this radar allow you to search for targets and work in target designation mode. The station can detect small air targets like anti-ship missiles at a distance of 70-80 kilometers. To counter the enemy's electronic systems, ships are equipped with a multi-range EW complex.
The CETRIS C3 combat information management system (CICS) is based on two main subsystems: the Saab Systems 9LV mk3E armament control complex and the MAST information support system. All components of the information management system are based on modern digital components. For the convenience of transmitting orders and instructions on ships like Visby for the first time in world practice, a special electronic system has been applied. Any crew member, using a special terminal, can receive in electronic form all the documents to which he has access. A communication system with other ships and command is similarly constructed.
The latest Swedish corvettes can independently search for enemy submarines. For this, they are equipped with a CDC Hydra hydroacoustic complex. The complex includes a passive towed hydroacoustic station, as well as an active type station that is lowered and located in the hull. In addition, the ship carries several remote-controlled vehicles that can be used to search for submarines. Hydroacoustic complex collects information from all stations and transmits data on detected targets to the control system weapons. Of particular interest is the station installed in the forward part of the ship hull. Having a relatively narrow beam, it can be used to search for sea mines.
When creating a complex of weapons of corvettes of the type Visby, the authors of the project provided for the possibility of "specialization" of a ship to perform specific tasks. In this case, all ships carry several common weapons systems. Before the superstructure, a Bofors 57 mm Mk3 artillery mount is installed on the corvettes with an automatic 57 caliber mm gun. This gun is capable of firing at a rate of up to 220 shots per minute and hit targets at a range of up to 10-11 km. High-explosive fragmentation projectiles for the gun are equipped with a controlled remote fuse, which allows to detonate the ammunition at the right time and “cover” the target with fragments. This, in particular, compensates for the relatively small caliber of the gun. In the stowed position, the artillery installation is located under the shielding casing of composite materials.
The design features of the Visby ships allowed them to be equipped with various weapons, in accordance with the wishes of the naval forces of Sweden. So, the first four ships (from Visby to Nyköping) are intended to search for submarines and sea mines, and also must accompany escorts. In this regard, the corvettes carry universal torpedo tubes. This armament is located in the stern of the ship and in the stowed position is closed by guards that do not protrude beyond the hull. In the forward part of the hull, next to the artillery installation, there are eight Alecto jet-bombs, which can use anti-submarine and anti-torpedo ammunition. The control system of the Alecto complex, working in conjunction with the ship's BIOS, allows you to simultaneously repel torpedo attacks from two directions.
The fifth ship of the Visby type (Karlstad) has a different set of weapons. It is assumed that this corvette will detect and attack enemy ships, for which it carries the corresponding guided missile weapons. Instead of torpedo tubes in the stern of the ship, there are launchers of anti-ship missiles Saab Bofors Dynamics RBS 15 Mk2. The use of such weapons will allow the Karlstad corvette to attack enemy ships at a distance of 200 kilometers. In addition, next to the anti-ship missile launchers, it is planned to install the Saab Bofors Dynamics RBS 23 BAMSE anti-aircraft missile system with vertical-start ammunition. The use of this air defense system will help protect the ship from aviation and enemy missiles in a radius of 15 km. There is information about the placement in the rear part of the corvette automatic gun caliber 30 mm.
Anti-submarine Visby corvettes can carry one Augusta A109 helicopter with the appropriate electronic equipment. If necessary, the helicopter can land on any of the ships of the series, but the hangar is only available on three of them: Helsingborg, Härnösand and Nyköping. In addition to the helicopter, the ships carry fuel and ammunition necessary to destroy enemy submarines.
According to reports, the Visby corvette radioelectronic complex is designed in such a way that the crew can search and attack targets without including any emitters. If necessary, ships can receive external target designation. It should be noted that the decrease in radar, infrared and acoustic visibility has a good effect on the actual characteristics of the latest Swedish corvettes. A number of sources mention that modern radar stations in calm can detect the Visby ship at a distance of no more than 20-22 kilometers. For waves, the detection distance is reduced to 11-13 km. Thus, using passive means of detection, the corvette can gain a great advantage over the enemy. In addition, the stated characteristics of electronic systems and weapons suggest that the use of radar or active sonar station does not reduce the combat potential of the corvettes. Thus, the detection range of the Ericsson Sea Giraffe AMB radar and the firing range of Saab Bofors Dynamics RBS 15 Mk2 missiles near 200 km in theory allows the latter of the Visby corvettes to attack enemy ships before they can detect it.
In the spring of 2012, Saab completed the renovation and modernization of the lead ship for the Visby project, commissioned by the Swedish Ministry of Defense. During the upgrade, the ship received about 60 various equipment and weapon upgrades. In particular, the systems of detection and communication, anti-submarine weapons, as well as equipment designed to work with helicopters were refined. In 2014, it is expected to complete a similar modernization of other anti-submarine corvettes.
Despite its modest size and small number, Visby-type corvettes are among the most interesting and high-tech ships in the world. In addition, during this project, Swedish shipbuilders were the first in the world to create and build a series of warships with extensive use of stealth technology. The claimed features of the corvettes look interesting and attract attention. However, the combat capabilities of the five ships raise some questions. Over the past years, Visby project corvettes in the ranks of the project have participated only in exercises and have never been able to show their potential in real operations. However, in this case, they remain the world's first invisible warships.
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