Dobrynya Nikitich-class icebreaker

In the mid-1950s, the Soviet Union began developing a new diesel–electric icebreaker design that could meet the needs of both civilian and naval operators. At the time, the merchant marine relied largely on ageing steam-powered icebreakers, many of which had been built during the Imperial Russia era and would reach the end of their operational life in the coming years. In addition, the Soviet Border Troops possessed just one ice-capable vessel for patrolling the country's northern border, Project 52K patrol ship Purga, which had been laid down already in 1938 but did not enter service until 1957. Technical development of the new icebreakers was entrusted to Leningrad-based Central Design Bureau No. 15, today known as Central Design Bureau "Iceberg" and part of the state-owned United Shipbuilding Corporation, which based the hull lines on the Swedish-built steam-powered icebreaker Eisbär which Germany had handed over to the Soviet Union as war reparations in 1946. Discussions during technical meetings sometimes became heated as naval architects tried to include both civilian and naval requirements into the design. One of the sources of disagreement was the bow propeller which was considered essential for icebreaking operations in the Baltic Sea and other non-Arctic waters but susceptible to damage in heavier Arctic ice conditions. Once the final design had been developed, the construction was awarded to the Leningrad-based Admiralty Shipyard. The first series, which consisted of largely similar triple-screw icebreakers, was built at a rapid rate: the hulls were assembled side by side on the slipway and launched at a technical readiness of 60–80%. In 1960–1971, the shipyard delivered up to three vessels annually, often in different configurations, while simultaneously implementing various technical improvements devised during the operation of the first vessels of the series. The second series with eight twin-screw Project 97P patrol ships and one research vessel was built in 1973–1981. With a total of 32 vessels built in various configurations over more than two decades, Project 97 and its subclasses are the largest and longest-running series of icebreakers and icebreaking vessels built in the world. With the exception of nuclear-powered icebreakers, they were also the only domestically-built post-war icebreakers in the Soviet Union and later Russia until the construction of Project 21900 icebreakers in the late 2000s. == General characteristics ==

With the exception of few heavily-modified variants, all Dobrynya Nikitich-class icebreakers had a length overall of and a beam of . Fully laden, the vessels drew between of water corresponding to a full load displacement ranging from . The later patrol ship and research vessel variants were somewhat larger than the early icebreakers. The hull form, derived from an older Swedish-built icebreaker, featured a round midship with pronounced tumblehome and practically no flat bottom or sides. While the curved hull lines resulted in low resistance and high maneuverability in ice, the vessels were very uncomfortable in open water due to excessive rolling. All ships shared the same diesel–electric power plant with three direct current (DC) main diesel generators. The 10-cylinder 13D100 () two-stroke opposed-piston main diesel engines were in fact reverse-engineered Fairbanks Morse 38 8-1/8 diesel engines manufactured by the Malyshev Factory in the Ukrainian Soviet Socialist Republic. The engines were coupled to double-armature DC generators (2 × 625 ) that provided power to PG-147 () DC propulsion motors driving two fixed pitch propellers in the stern and a PG-146 () DC motor driving a propeller in the bow. During initial icebreaking trials, the icebreakers were able to break thick level ice with a snow layer on top at very slow but continuous speed. == Variants ==

Project 97 Three Project 97 icebreakers were built for the Soviet Navy: Dobrynya Nikitich for the Northern Fleet, Project 97AP Project 97AP () was an armed patrol icebreaker variant built for the Soviet Navy. Built with increased autonomy time and operating range, they were intended to patrol the western and eastern ends of the Northern Sea Route. The armament was later dismantled. Peresvet, which was previously assigned to the Northern Fleet, was decommissioned in 2011 and later scrapped. Project 97D Project 97D () was a hydrographic survey vessel variant built for the Ministry of the Maritime Fleet of the Soviet Union to survey the Northern Sea Route. While otherwise nearly identical to baseline Project 97 icebreakers, these two vessels were fitted with additional scientific facilities, echosounders to conduct hydrographic survey, and accommodation for an additional 14 personnel. However, they were also used for icebreaking operations from time to time. == Derivative designs ==

Project 97B '', the sole Project 97B hydrographic survey vessel Project 97B () was a hydrographic survey vessel variant built for the Hydrographic Office of the Soviet Navy. Unlike the preceding Project 97D built for civilian service, Project 97B was a more radical departure from the original Project 97 icebreaker design with increased length and displacement to increase range and endurance, as well as an enlarged deckhouse to accommodate more personnel on board. , Vladimir Kavrayskiy remains in service with the Northern Fleet as the stationary barracks ship PKZ-86 in Murmansk. Project 97P , one of eight Project 97P icebreaking patrol ships built for the Soviet Navy and Soviet Border Troops Project 97P () was developed as a response to the renewed interest of the Soviet Navy and Soviet Border Troops on icebreaking patrol ships after United States Coast Guard and Canadian Coast Guard icebreakers began appearing more frequently near the country's northern maritime borders. New icebreaking patrol ships were needed because existing Soviet naval vessels could not operate in ice-covered waters and large icebreakers, in addition to being unarmed and operated by civilians, could not be distracted from their primary mission of escorting merchant ships. Central Design Bureau "Iceberg" selected Project 97 as the design basis following positive operational experience and the difficulties associated with developing a new design. , four Project 97P patrol ships remain in service: Ivan Susanin with the Pacific Fleet and Ruslan with the Northern Fleet, both with their armaments removed, and Neva and Volga with the FSB Border Service. Project 97N '', the only Project 97N research vessel Project 97N (), the final variant developed based on the Project 97 icebreaker design, was a research vessel commissioned by the State Committee for Hydrometeorology and Environmental Control of the Soviet Union to conduct scientific research in the poorly-studied transition zone between open water and the polar ice pack. In addition to adding extensive scientific facilities and additional accommodation, the hull lines were given more pronounced sheer and flare to reduce the likelihood of waves breaking over the bow. The only Project 97N ship, Otto Schmidt, was in service in 1979–1991, and was sold for scrap in 1996. == References ==