Project 955B Borey-B

The further development of Project 955 will be the nuclear submarines Borey-B. From 2018 it was intended to begin the draft design of the upgraded submarines of the project 955B with new jet propulsion and on-board equipment. On contemporary nuclear submarines steam turbines are linked to reduction gears and a shaft rotating the propeller, but more advanced western submarines use a pump-jet propulsor.

Russian submarine B-871 Alrosa is an diesel-electric Kilo-class submarine that joined the Soviet Fleet in 1990 and is active with the Russian Black Sea Fleet as of 2011. Instead of a conventional propeller Alrosa uses a pump jet propulsion system. Kilo submarine B-871 ("Alrosa") launched in 1989 (with pumpjet? or retrofitted?) has a large pumpjet with 7 stators and 11 propulsors. It spends more time in dry dock for repairs and upgrades to its pumpjet than at sea.  The pumpjet appears to be of excessive size - perhaps implying Alrosa is a test vehicle for a pumpjet intended for much larger SSN's or SSBNs.

The term pumpjet defines a hydrodynamic propulsor that consists of a rotating vane system operating in an axisymmetric diverging shroud or duct to diffuse, or reduce, the inflow velocity. In addition to the rotating vane system, a stationary vane system is used at the exit to take out the whirl. The interest in pumpjets has resulted primarily from efforts to develop propulsor systems for both high-speed surface and submerged vehicles. The attractiveness of pumpjets for high-speed applications originates from the ability to design the propulsor to operate with inflow velocity at the vanes lower than the forward velocity of the propeller body, so that the blading is less apt to cavltate than unshrouded blading. Reduction in the velocities relative to the rotating blade system can normally be accomplished only if the shaft speed and the circumferential flow velocity are also reduced. In most cases, this leads to high-torque propulsors of low shaft speeds.

The pumpjet has several advantages over propellers. It may offer a significant reduction in cavitation inception number because the pressure may be build up around the impeller by decelerating the flow with proper shaping of the shroud. The shroud masks some of the radiated noise that might be generated inside the pumpjet. The rotor requires only one drive shaft in contrast to the two required for counterrotating propellers. The whirl is taken out with stationary vanes.

The problem of propulsor cavitation is largely dependent on the degree to which cavitation must be avoided. It has been well established that limited cavitation occurring within the blade passages of pumps, propellers, and pumpjets does not affect the propulsor performance or efficiency, but strongly developed cavitation can lead to complete performance breakdown and falloff in shaft torque, as well as blade erosion. However, the problem is considerably complicated when it is necessary to avoid local incipient cavitation as a possible source of noise at specified vehicle speeds and depths. In general, for a given disk area and mass flow, as advance ratio is increased (shaft speed decreased) the cavitation performance improves. Also, for a given advance ratio and mass flow, as the disk area is increased, the cavitation index improves.

A second form of cavitation occurs in shrouded propulsors due to the presence of secondary flows such as tip-clearance leakage flow. Tills flow, resulting in a tip vortex, generates cavitation in the clearance gap itself. The leakage flow also impinges on the top of the stator system, causing periodic cavitation. In pumpjets it is usual to find that the cavitation resulting from secondary floz/s occurs before blade surface cavitation. However, research provided design criteria that, if properly applied, will give overall propulsor cavitation performance equal to limits predicted for blade surface cavitation.

The Le Triomphant boats are the latest addition to the French missile submarine force, the FOST (Force Oceanique Strategique). They are referred to as the SNLE-NG (SSBN, New Generation). The Le Triomphant class are quieter than its predecessor, propulled by a K-15 reactor, with 1 shaft and a pump jet propulsor. A Ohio Replacement scale model displayed at the Navy League’s 2015 Sea-Air-Space Exposition, indicates that the Ohio Replacement will feature a pump-jet propulsor visually similar to the one used on Virginia class SSNs, and earlier Seawolf-class SSNs.

In a pump jet system, an impeller or rotor is mounted (e.g., spline fitted) directly on the propeller output shaft in place of the propeller. There are typically no modifications to the drive train, cooling or sealing components. A ducted housing surrounds the rotor. Such a system has the advantages of protecting the rotating elements from interference with and damage by foreign objects in the water, and improving the efficiency and performance of the propulsion system. Another benefit inherent with the pump jet is a directed jet of water that results in greater steering response. More pertinent to the present application, the pump jet propulsor, with its high-efficiency shrouded design, alters the radial noise field and provides an opportunity to also alter the noise spectrum.

In one conventional type of jet pump apparatus, the housing comprises a rotor housing connected to a stator housing, the former surrounding the rotor and the latter being downstream of the rotor. The rotor is driven by the powerhead via a drive train. Rotation of the rotor impels ambient water from the housing inlet to the housing outlet. Due to manufacturing tolerances, during rotation the rotor can wobble on the propeller shaft, causing the tips of the rotor blades to contact the opposing surrounding surface, thereby causing that surface to wear. If the inner circumferential surface of the rotor housing were placed in close surrounding relationship to the rotor, without an intervening member, then that rotor housing surface would experience wear. If that wear were allowed to continue indefinitely, replacement of the worn rotor housing could become necessary.

There was essentially no information about this project in open sources as of November 2017. According to the Chief of the General Staff of the Armed Forces, Army General Valery Gerasimov, work on a promising cruiser has already started. In turn, Admiral Vladimir Korolev, Commander-in-Chief of the Navy, said on 17 November 2017 that after Borey-B, the Russian military-industrial complex will build the fifth generation nuclear submarines. This is a multi-purpose submarine project "Husky". Formally, they will not be strategic, but are designed to solve a wide range of tasks, including in the interests of nuclear deterrence forces.

The new "Borey-B" project is included in the new the state armaments program (LG) for 2018-2027. A special emphasis will be placed on the development of a new GPV on the development of nuclear deterrence forces and the delivery of precision weapons to the troops. Work for the design of a strategic nuclear submarine cruiser would begin in 2018, completion of tests and transfer to the Navy are scheduled for 2026. It is supposed that the boat will receive the hull of its predecessor (the Borey-A project), but thanks to the installation of a new jet propulsion unit, its noise level will be significantly reduced. The serial construction of Boreev-B is planned to begin in 2023; there will be at least four of them.

The Commander-in-Chief of the Navy, Admiral Vladimir Korolev, in November 2017, reported that the timeframe for the construction of the new Boreev will become clear after the final design of these ships has been completed. "From 2018, we begin to work actively on this project, I think it will be soon, we will determine the specific dates based on the results of the first stage, that is, the formation of a draft outline," the commander said.

The strategic nuclear submarines (nuclear submarines) of the Borey-B Project 955B were not included in the state armament program for 2018-2027, with the result that after 2023 Sevmash will build six more submarines of the Borey-A Project 955A, in the Northern and Pacific Fleets, a source in the military-industrial complex told TASS 21 May 2018. “After analyzing the proposals for the development of the Borey-B nuclear submarine, it was decided to abandon them, since the construction project for these submarines does not meet the criterion of“ cost-effectiveness ”. Instead of them, Borei-A is included in the final version of the state armament program until 2027, ”the agency’s source said.

Thus, the source noted, with the transfer of "Borey-A" the number of new strategic submarines in the fleet's combat strength will reach 14 units: 11 - of the "Borey-A" class, and 3 - of the "Borey" class.