Project 1239 Sivuch
Dergach / Bora class
Guided Missile Corvette
The Project 1239 Sivuch small missile air cushion ship is primary intended for coast defense operations. These very large surface-effect ship corvettes have proven mechanically unreliable. Completion of these units was much-delayed and they probably are not effective combat units. Two vessels have been built by the plant for the Russian Navy according to this project: «Bora» (1989) and „Samum“ (1999). The two ships were in service, with a future series intended for Black Sea/Baltic Fleets of Russian Federation.
The key design feature of this hydrodynamic configuration is an air cushion that separates the hull from the water surface, combined with maintaining contact with the water surface by means of sidewalls. The latter provide very low resistance to motion of the ship, but significantly reduce air loss from the air cushion area, partially unload the cushion, increase course-keeping stability and ship steering performance.
The Russian missile carrying hovercraft is meant to carry out missile attacks on ships. It is the largest military hovercraft unmatched anywhere in the world. With the displacement of 1000 tons, the craft has a cruising speed of 100 kilometers an hour. With blowers on, the air cushion enables achieving a speed of more than 50 knots. In addition, intermediate speed modes with reduced air supply to the air cushion zone are available. This is called «multimode motion capability» – a property no other ship in the world can boast.
The transformation capability of hydrodynamic platform and propulsion system ensures a broad speed range enabling operating the ship as a part of naval force. High reliability and reparability of the hull of catamaran type is made from corrosion-resistant aluminum-magnesium alloys, lift-off and droppable flexible guard and full speed propellers have been proved during long-term operation of the ship. Combined diesel-gas turbine set and stores of fuel and lubricants to ensure an operational range of 800 miles at full speed on air-cushion and 2500 miles at speed of 12 knots when the ship is hullborne. Sea keeping qualities provide the use of weapons at speed up to 30-40 knots at sea state up to 5 points and possible hullborne stay at sea state up to 8 points.
The missile hovercraft was designed by the State-owned Unitary Enterprise Central Marine Design Bureau «Almaz» (Saint-Petersburg). In the USSR, several design organizations worked on sidewall hovercraft, built several large-scale self-propelled models and passenger ships. The Almaz Central Marine Design Bureau developed a combaant sidewall hovercraft – Bora-class small missile ship (SMS). Full-scale development began in 1976 with extensive research efforts. Designers had to address a number of challenging technical problems, carry out a series of testing of towed and self-propelled models on tight schedule. Testing the 50-t Ikar-2 self-propelled model substantiated the surprisingly high sea-keeping capacities of sidewall hovercraft.
After a comprehensive analysis of the pros and cons of the different propulsion unit options, a CODOG- CODAG diesel/gas-turbine plant was selected: diesels were used for cruising and gas turbines jointly with diesel engines for full-speed running. For high-speed running, down-take steerable pods were used with propellers driven by gas turbines. The set of out-of-the-box technical solutions adopted in the detailed design phase resulted in a unique SMS unrivalled in global shipbuilding industry. Tests of this new Russian missile carrying hovercraft began in the Baltic Sea in late 1999. The tests of the hovercraft were expected to finish in early 2000, and then the craft was adopted by the Russian Baltic fleet.
The missile hovercraft is intended to combat surface ships, fast boats and other enemy’s transport within all water area of closed sea battle zones and in close region of open seas. It can operate independently or as a part of a designated naval force consisting of similar and different ships. Well-balanced weapon assets and high sea-keeping qualities of the ship’s hydrodynamic platform ensure more effective detection of surface and air targets against radar countermeasures, and to attack them using missiles and gun mounts without limitation at sea state up to 5 points inclusively. Active and passive electronic countermeasure devices of the ship provide effective protection of the vessel being a target of enemy’s gun. Anti-diversion and anti-terrorist defense system of the ship being on raid or staying in bases is supported by corresponding surveillance system and weapon asset.
It is armed with 8 Mosquito missiles which can strike targets on the sea and on land. The hovercraft has 20 anti-aircraft missiles, an artillery complex, a machine-gun and an interference creating device. The hovercraft has an aluminium hull. Though it's a light craft, its seaworthiness is very high. The hovercraft can be on an autonomous voyage for 10 days. One refueling is enough for 2,500 miles. The complement is 68 men. As the chairman of the state commission overseeing the tests, the first deputy commander of the Russian Baltic Fleet, Vice-Admiral Alexander Brazhnik, said the hovercraft showed excellent performance in stormy conditions and carried out the first missile launches and artillery fire practice.
The future of sidewall hovercraft (skeg-type air-cushion vessels) – fast and seaworthy – looks very promising. Today the level of shipbuilding technologies and accessory equipment in Russia makes it possible to exploit the success in the development of combat sidewall hovercraft for the Russian Navy. Retaining the basic technical solutions fine-tuned on Bora-class SMS (hull lines, the principle of air delivery to and distribution in the air- cushion area, flexible skirt retraction scheme, diesel-gas turbine power plant), it is feasible to develop an upgraded version of the project offering enhanced operational performance and extended range of use.
Relying on the operating experience with Bora-class ships, Almaz has considered alternative propulsion systems and the use of water-jet propulsors in more detail, which drastically simplifies the propulsion system and motion control in all modes. Abandoning the down-take steerable pods frees the afterbody to accommodate a helipad and a sliding hangar, while the use of unmanned aerial vehicles for strike missions increases the mission effectiveness and safety for the ship. Owing to its high speed combined with outstanding steering performance, the ship can effectively take part in operations related to the preparation and fire support for amphibious landings using its multiple rocket launchers.
A design feature of a sidewall hovercraft hull is two horizontal keels along the whole hull length, which it can rest on in a coastal strip or shallow water as on fixed supports. Moving on an air cushion, the ship can negotiate offshore shoals and approach unequipped shores up to a depth of 1 m, where, going aground on its keels, it can carry out cargo handling, rescue or special operations. Thus, using a fast and seaworthy universal platform, it is possible to develop strike missile ships, amphibious fire support ships, rapid response rescue ships, amphibious ships, special and small ships of different purposes.
The R&D groundwork laid by Almaz gives reason for a more comprehensive approach to the development of sidewall hovercraft. Design studies of high-speed sidewall hovercraft based on the testing results for the Strepet self-propelled model have demonstrated the feasibility to develop ships with a displacement of about 1,000 tons and speeds of over 100 knots. The speed performance and combat capabilities of such ships become commensurate with the characteristics of wing-in-ground (WIG) effect vehicles, the attacks of which cannot be detected by satellites and have a very high mission accomplishment probability. In this context, it should be noted that sidewall hovercraft are easier, cheaper and more reliable in operation than WIG vehicles.
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