Project 12700 Aleksandrit Class
Aleksandr Obukhov Fleet Minesweeper
The minesweepers have a full displacement of 890 tonnes and are 61 meters (200 feet) in length and 10 meters wide. The ship’s major characteristics are speed – 16.5 knots, and crew - 44 persons. The vessel is designed for mine protection of naval bases and coastal areas; for detection and destruction of mines of all types; for mine defence of vessels during voyage, of EEZ and undersea mineral resources areas; for antimine reconnaissance as well as for minelaying. During the time of low probability of mine threats a vessel can be used for protection of certain sea areas or for training of naval personnel.
Typical ship hulls are normally made of steel which is magnetic and thus entails the well-known disadvantages thereof, especially during war-time conditions. Several studies have indicated that for hulls longer than about 200 feet, even carbon fiber composites do not provide the necessary stiffness and strength required for the hull. Furthermore, the cost of carbon fiber composites which is currently $12-18 per pound of carbon fiber as compared to $0.45-$0.50 per pound for high strength steel [US prices], would be prohibitive for ships of this size. Low cost, high performance composite materials such as glass fiber composites (GRP) using resin transfer molding processes which are presently used in patrol boats, Corvettes and mine hunters, do not offer the stiffness nor the in-plane strength required for long hulls of combatant ships or other large commercial ships.
The load-carrying mechanism for long ships is by axial tension and compression in the hogging and sagging mode between waves. The technology of composite sandwich construction, which is common in smaller ship lengths or boats, does not satisfy the carrying capability for sea loads in longer ship hulls. The in-plane strength of the composite material is therefore critical. Moreover, for small ships and boats, the bending strength of the composite material is critical. The present technology of composite sandwich construction which is common in smaller ship lengths or in boats would not add to the carrying capability for sea loads in long ship hulls.
The entire 62-meter hull of the ‘Aleksandr Obukhov’ (Project ‘Aleksandrit’) is made of monolithic fiberglass. It took over a year to form the hull, which has no magnetic signature, in a specially designed matrix. The ‘Aleksandr Obukhov’ is the largest plastic-hulled ship ever made in Russia. This technology in the Russian military shipbuilding introduced for the first time. The vessel is capable of detecting and destroying all kinds of modern sea mines, even if they are silt-covered.
The advantage of a non-magnetic housing design is its high strength, which allows for greater survivability of the ship during operations in mine operations at sea. The duration of life of such a body is several times greater than that of the magnetic steel casings. There was also a significant reduction in weight.
Russian sources report the "Alexander Obukhov" has a unique hull, the world's largest body of reinforced fiberglass formed by vacuum infusion. The Mid-Nevsky Shipyard in St. Petersburg is said to be the only company in the country that had mastered the technology of creating monolithic hulls up to 80 meters long. An important advantage for such a "fiberglass" ship is increased body strength and a 20% reduced weight (250 tons of equipment and without add-ons), and the absence of metal, which can trigger mines. The non-magnetic body - one of the most important qualities for a ship mine defense. Furthermore, the service life of such a casing in a corrosive saltwater larger than the housing of the magnetic steel, - more than 30 years.
Glass-plastic production in St. Petersburg has been mastered in the 1960s. Today, the technology of building ships and vessels made of composite material improved in accordance with the international scientific and technical progress. There are three ways to obtain composites: contact molding, RTM Light technology and vacuum infusion.
Contact molding method - the easiest way to produce polymer composite materials. It is used in the manufacture of large parts with complex configurations. Stekloarmiruyuschy material impregnated with resin by hand with a brush or roller. The impregnated material (laminate) is placed in a mold where it is rolled by special rollers. Thus it is removed from the air bubbles and distribute the resin evenly throughout. Laminate hardens at normal room temperature, whereupon the product was removed from the mold and processed. Light RTM - is a closed molding process under vacuum, wherein the reinforcing material is sandwiched between two rigid half-molds. Resin injection pressure occurs using specialized equipment. This method is economically advantageous to use in mass production of products is relatively small in size.
The hull of "Alexander Obukhov" is created by the method of vacuum infusion . Large matrix, repeats the shape of the hull, is lined with a special reinforcement material (fiberglass or carbon cloth). Depending on whether it is a body portion, the number of layers of such a "tissue" can be up to several tens. The material is fully covered with an airtight film, to which is attached a plurality of tubes. After they served resin which permeates all layers of reinforcing material due to the vacuum created by the film. The result is a durable and lightweight product - the hull, "bathed" in shape. Vacuum infusion and RTM technologies reduce the duration of manufacturing structures and provide a virtually complete absence of harmful emissions.
As reinforcing materials are used glass and carbon fabrics of different weave. Most of them were manufactured in Europe, but gradually Sredne-Nevsky Shipyard goes to domestic composite materials. Domestic resins are the latest tested and will be used in the construction of the following vehicles. The issue of import substitution foams and auxiliary materials is still open - research continues. It will be held on board the latest countermines armed with automatic control system. Along with this, the ship will be able to use conventional trawls.
A total of 26 sailors of the Russian Navy would be new trawler crew members. According to Viktor Chirkov, this number is able "to provide a fully electric propulsion ship, the use of all means to ensure the safety of navigation, as well as perform any task on search and destroy mines."
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