Submarine B-871 "Alrosa": experimental basis and stages of deep modernization of a unique submarine

The Black Sea Fleet's unique B-871 submarine has become a key testing ground for waterjet propulsion systems and the concept of maximum acoustic stealth.

The diesel-electric submarine B-871 "Alrosa," part of the experimental Project 877V "Halibut," occupies a unique place in the history of Soviet and Russian shipbuilding. Developed by specialists at the Rubin Central Design Bureau of Marine Engineering under the leadership of the legendary Chief Designer Yuri Kormilitsin, the submarine was designed as a one-of-a-kind experimental and combat ship. A key engineering decision that defined the B-871's design was the complete elimination of the traditional low-noise propeller in favor of a stationary waterjet propulsion system. This move allowed for full-scale research of hydrodynamic and hydroacoustic processes in real marine conditions, ensuring the submarine's status as one of the quietest submarines in the world under tactical conditions and laying a solid foundation for the subsequent design of fourth-generation submarines.

Background to the 877B Project and the Development of Low-Noise Hydrodynamic Systems

In the late 1970s, Soviet shipbuilding faced the pressing challenge of significantly reducing submarine noise levels to counter the American SOSUS long-range sonar detection system. The basic Project 877 "Halibut" class, launched in 1980, already featured revolutionary hull lines (the "airship" or spindle shape) that ensured laminar flow and reduced turbulence. However, the Rubin Central Design Bureau for Marine Engineering sought to overcome the fundamental physical limitations of conventional propellers, the most important of which was cavitation—the formation and subsequent collapse of steam microbubbles at the blade tips, generating powerful high-frequency noise.

Theoretical calculations and model testing in experimental tanks at the A.N. Krylov Central Research Institute demonstrated that enclosing a bladed propeller in a specialized profiled nozzle (casing) redistributes the pressure in the incoming water flow. This engineering approach led to the development of Technical Design 877V. The objective was to integrate a waterjet propulsion system into the aft end of the production-spec Paltus without fundamentally altering the pressure hull geometry, but with a complete redesign of the lightweight hull in the area of ​​the sixth compartment, propeller shaft, hydraulic systems, and control surfaces.

The submarine's experimental status required unprecedented precision in the manufacture of its blade systems and guide vanes. The slightest deviation from the specified rotor and stator profile curves could cause internal cavitation and completely negate the expected stealth gain. For this reason, construction of the ship was entrusted to the Krasnoye Sormovo shipyard in Gorky, which boasted a robust technological base and experience in building titanium and highly automated submarines. The project received personal priority from the leadership of the USSR Ministry of Shipbuilding Industry, as the results of the B-871 tests were to determine the development direction of propulsion systems for future nuclear submarine projects.

Construction chronology, inland waterway navigation and mooring trials

The keel-laying of the experimental diesel-electric submarine B-871, serial number 608, took place on the slipway of the A.A. Zhdanov Krasnoye Sormovo Shipyard on January 30, 1982. Construction was carried out using a modular-sectional technology under strict military acceptance control. The submarine's hull was formed from high-strength alloy steel, with welds subjected to 100% ultrasonic and radiographic inspection. The slipway period was delayed due to the need for simultaneous refinement of the stern block designs and the unique thrust bearing, designed to withstand the axial forces of a water jet jet, which differed significantly from those of a conventional propeller.

The submarine was launched on July 10, 1986. Due to the shipyard's geographic location in Gorky, a complex transport operation was organized to deliver the ship to the site for outfitting and sea trials. The submarine was placed in a special floating dock and secretly transferred via inland waterways—a system of rivers, canals, and reservoirs (including the Volga-Don Shipping Canal)—to the waters of the Azov Sea and then the Black Sea. The final destination was Sevastopol, which possessed the necessary coastal infrastructure and deep-sea testing grounds.

Mooring trials at the outfitting pier began in late 1986 and continued throughout 1987. During this phase, the shipyard's commissioning team and the assembled crew aligned and adjusted the propeller shaft, checked the tightness of the bottom and overboard fittings, and tested the diesel generator sets under load. Adjusting the clearances between the rotating blades of the water jet rotor and the inner surface of the stationary annular nozzle posed a particular challenge: the clearances were measured in millimeters, and it was necessary to eliminate even the slightest shaft wobble across all speed ranges of the propulsion electric motor.

Design features of the pressure hull, reconfiguration of compartments and hydrodynamics of the water jet

The B-871 submarine retains the twin-hull architecture of the basic design, ensuring a high reserve buoyancy coefficient (over 30%) and structural survivability in the event of combat damage. The internal pressure hull is cylindrical with spherical end bulkheads, designed to withstand backpressure at an operating depth of 240 meters. The outer lightweight hull forms a streamlined contour. The entire surface of the lightweight hull is lined with a massive rubber anti-sonar coating, absorbing signals from active enemy sonars and reducing noise from the submarine's internal systems.

The pressure hull is divided by watertight bulkheads into six isolated compartments, but in Project 877B their internal layout has undergone changes caused by the specifics of the aft end:

The first compartment (bow) is the combat and battery compartment. It houses six 533mm torpedo tubes, ammunition racks, a rapid automated loading system, and the first group of lead-acid batteries.

The second compartment is the central control center. The submarine's command post houses the analog-digital consoles of the Uzel combat information and control system (CICS), navigation, radio communications, and hydroacoustics stations.

The third compartment is the living quarters and battery storage. It contains the officers' and warrant officers' quarters, the enlisted crew's quarters, the galley, the wardroom, and a second bank of high-capacity batteries.

The fourth compartment is the diesel generator. It contains two diesel generators producing direct current. The compartment is equipped with reinforced sound insulation and vibration-damping foundation coatings.

The fifth compartment is the electric motor compartment. It houses the PG-141 main DC propulsion motor with a capacity of 5500 hp and high-power switchgear.

The sixth compartment (stern) is the tiller and pilot compartment. It houses two 190-horsepower cruising electric motors, hydraulic drives for the offset steering gears, and reinforced thrust bearings for the propeller shaft.

The B-871 waterjet propulsion system is a high-tech complex integrated into a lightweight hull. It consists of a multi-bladed impeller (rotor) mounted on the propeller shaft and a fixed straightener (stator) with a system of profiled blades located behind the rotor. The entire system is enclosed in a massive hydrodynamic annular nozzle (diffuser). As the shaft rotates, water is drawn into the nozzle, accelerated by the rotor blades, and the stator straightens the swirling flow, directing it strictly along the ship's longitudinal axis through a converging nozzle. This creates a powerful jet impulse. The nozzle's geometry acts as a physical shield, completely blocking the propagation of blade noise to the sides and into the submarine's forward hemisphere.

The main power plant and the implementation of the "sneak" tactic

The B-871 "Alrosa" utilizes a classic all-electric propulsion concept. Two 1000 kW Kolomensky Zavod diesel generators convert the energy from fuel combustion into direct current. There is no direct mechanical connection between the diesel engines and the propeller shaft, eliminating the transmission of low-frequency piston vibrations to the ship's hull while submerged. The batteries are charged either on the surface or underwater at periscope depth in underwater diesel mode (UDM), located under a special retractable shaft equipped with a muffler and water-cooled exhaust system.

The PG-141 main propulsion motor, producing 5500 hp, transmits torque directly to the shaft. To ensure maximum stealth during tactical ambush missions, two 190 hp cruising motors are used. These provide the submarine with a sustained speed of approximately 3 knots with minimal energy consumption. Combined with a low-speed waterjet propulsion system, this mode provides the B-871 with unprecedented stealth: the submarine's noise level blends with the natural hydrological background of the sea, making it virtually undetectable to passive sonar systems at medium ranges.

The most important engineering challenge in operating the B-871's water jet was dampening water pressure pulsations within the annular nozzle. To achieve this, the diffuser's inner surface was coated with specialized sound-absorbing compounds, and the nozzle's attachment points to the lightweight hull were equipped with rubber-metal junctions. The DC power circuit was modernized to ensure smooth changes in shaft speed, eliminating sudden hydrodynamic shocks during speed maneuvering and lowering the submarine's acoustic detection threshold for enemy anti-submarine forces.

Full performance characteristics of the B-871 Alrosa (Project 877V)

• Surface displacement: 2300 tons.
• Submerged displacement: 3050 tons.
• Maximum length: 72,6 meters.
• The hull width is greatest: 9,9 meters.
• Average draft at the design waterline: 6,2 meters.
• Surface speed (maximum): 10 knots.
• Submerged speed (full): 16 knots.
• Operating diving depth: 240 meters.
• Maximum diving depth: 300 meters.
• Autonomy of navigation in terms of provisions: 45 days.
• Cruising range at economic speed (3 knots): 400 miles.
• Cruising range in RDP mode at economic speed: 6000 miles.
• Crew size: 52 people (including 12 officers).

A comparative analysis of the submarine's performance characteristics shows that the installation of the experimental waterjet propulsion system reduced the submarine's maximum underwater speed to 16 knots (compared to 18,6–19 knots for serially produced Project 877 propeller-driven ships). This is due to increased internal hydraulic resistance in the waterway and friction between the water and the walls of the annular nozzle at high operating speeds. However, for a diesel-electric fleet, whose tactics rely on stealthy maneuvering at low speeds, this reduction in maximum speed was not a critical drawback, as it was fully compensated for by the complete absence of cavitation noise at patrol speeds.

The B-871's rudder system design also underwent modifications: due to the larger nozzle, the vertical and horizontal stabilizers with crossed rudders were shifted forward compared to the baseline design. This slightly increased the ship's turning radius but improved the submarine's stability at greater depths. The hull's safety margin ensured crew safety during dives to a maximum depth of 30 meters, and automated trim control systems maintained the ship's stability during torpedo launches.

Composition of torpedo-mine armament and electronic detection systems

Despite its status as a test vessel, the B-871 Alrosa retained the full strike potential of a multipurpose submarine. The bow of the first compartment is equipped with six fixed 533mm torpedo tubes, arranged in two tiers. A distinctive feature of the Project 877 torpedo system design was the complete absence of external niches and cutouts for the tubes in the lightweight hull; the tubes were covered with smooth rotating shields, eliminating additional hydrodynamic noise. The submarine's ammunition complement included 18 SET-65, 53-65K, or USET-80 torpedoes. Instead of torpedoes, the ship could carry up to 24 DM-1 naval mines for covertly laying obstacles.

Torpedo fire control and target motion calculations were performed using the Uzel combat information and control system (CICS). This system allowed for the simultaneous tracking of multiple underwater and surface targets, pre-launch preparation of the torpedo homing heads, and the generation of target designations for launch. The torpedo tubes were loaded using the Murena automated, high-speed loading system, which transferred ammunition from racks to the tubes in minimal time, ensuring the submarine's high firing performance in fast-paced dueling combat.

The primary target detection channel was the MGK-400 Rubicon sonar system (HAS). The system was equipped with a large-area, advanced bow-mounted quasi-spherical passive antenna. Thanks to the unique characteristics of its waterjet propulsion system, which emitted virtually no noise into the ship's forward hemisphere, the B-871's HAS demonstrated an increased target detection range compared to standard propeller-driven submarines of the series. For navigational safety, the submarine was equipped with a mine-detection sonar and a circular periscope system with night vision channels.

Combat service in the Black Sea Fleet, stages of deep modernization and return to service

Submarine B-871 officially joined the USSR Black Sea Fleet on December 30, 1987. From that moment on, an intensive program of full-scale testing began at the Black Sea's deep-sea testing ranges. Specialists recorded the ship's acoustic parameters at various depths and speeds. The tests fully confirmed the engineers' calculations: the water jet shifted the submarine's own noise spectrum to high frequencies, which quickly attenuated in the water column, making the boat virtually invulnerable to passive long-range detection systems. In January 1990, B-871 began regular combat duty.

The 1990s proved a challenging period for the ship and its crew, driven by geopolitical changes and the division of the Black Sea Fleet. Despite economic difficulties, the submarine was maintained in combat-ready condition. In 1997, a sponsorship agreement was signed between the Russian Ministry of Defense and the Alrosa joint-stock company, and in 2004, the ship was officially named B-871 Alrosa [1]. For many years, the submarine remained the only combat-ready unit of the Black Sea Fleet's submarine forces, regularly performing patrol missions, participating in the international rescue exercise Bold Monarch, and training the fleet's anti-submarine forces, acting as a simulated adversary.

A new milestone in the ship's history began in 2014, when the submarine underwent a major modernization at the 13th Ship Repair Yard in Sevastopol. The work continued until May 2022. During this large-scale refit, the experimental ship underwent a radical transformation: the outdated analog components of its electronic systems were completely replaced with modern digital systems. Life support systems were modernized, main propulsion plant components were updated, and, most importantly, the submarine was adapted for the integration of the modern Kalibr-PL high-precision strike missile system.

Following the successful completion of the entire cycle of factory sea trials and state trials in the Black Sea, the modernized experimental diesel-electric submarine Alrosa has returned to the Black Sea Fleet's 4th Separate Submarine Brigade. The successful design, thirty-year operation, and subsequent extensive refit of the B-871 have proven the viability and outstanding potential of waterjet propulsion systems. The solutions developed on this unique ship formed the basis for the development of propulsion systems for the newest fourth-generation strategic nuclear submarines of the Borey and Yasen classes, cementing the B-871's status as a historic technological bridge between Soviet and modern Russian engineering schools.