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Acoustic Detectability of Project 885/885M Class Russian SSGN Secondary Propulsion System

By Bruce Rule - Feb 11, 2016


The Project 885/885M YASEN Class Russian SSGN ((also known as the SEVERODVINSK, GRANEY (NATO), and “Ash”)) secondary propulsion system – not to be confused with the PG-141 dc motor component of the hybrid (turbo-electric - turbine-reduction)) main propulsion system - will employ ring-motor technology to reduce the acoustic detectability of the secondary system which has a maximum speed capability of 4.5 knots. Back-up power for operation of this system can be provided by an ADH-1000B 1000 kW diesel generator, a design based on the 8DM-21 system produced by the Ural Diesel Motor Plant. The ADH-1000B also is used by BOREY Class Russian SSBNs.

Ring-motors, a patented US development (see below), have significant advantages over conventional electric motors. They are light-weight, compact (exceptional power-to-weight ratios) and have low vibration (noise) levels. Commercially-available ring-motors with a five hp rating weigh only two pounds (one kg) while an 800 hp motor has a diameter of only 36 inches (0.9m).

Ring-motors are ideal for submarine propulsion applications, especially where it is useful to locate the motor external to the pressure-hull as with deep-diving platforms. It is probable ring-motor technology will be widely used by future classes of Russian nuclear and diesel submarines.


The site provides the following description of a ring-motor:

“An inventive submarine features a propulsion drive arranged outside the pressure-hull which is arranged in the longitudinal direction of the submarine as an extension of its stern and comprises a housing and a first electric motor. The housing forms a preferably nozzle-shaped channel for a flow of water through the channel in a main direction of flow from an inlet to an outlet of the channel. The first electric motor features a rotor which is arranged in the channel and is supported rotationally in the housing, with the motor being embodied in a ring shape with a ring inner side and a ring outer side. Inventively blades to propel the submarine are arranged on the ring inner side of the rotor. An electric motor with such a ring-shaped rotor is frequently referred to in the technical literature as an “electric ring motor” or “RIM drive”.

“The support of the rotors in the housing and the torque compensation which leads to a reduction of the blade loading on full load of the blades arranged on the rotors for driving the submarine means that the noise emitted by the propulsion drive into the environment can be kept low and also the cavitation on the blades can be reduced.”


Title of the 2014 posting: Detailed Image of an AKULA Class SSN Maneuvering Thruster System Also Employed by BOREY Class SSBNs

If you go to, linked below, and scroll down to the fourth image (picture), you will find a photo of one of the two maneuvering thrusters used by AKULA Class Russian SSNs. BOREY Class Russian SSBNs also use this system. 

These AKULA/BOREY maneuvering thrusters - now known to be located well aft in deployable "tunnels" between the outer “light” hull and the pressure hull, and deployed, as shown by the image, when needed - are driven by two-speed PG-160 motors rated at 410 hp each. Use of the term “two-speed" confirms the thruster motors are ac with the different speeds achieved by changing the effective motor-pole configurations.

The most probable motor configurations - based on blade-tip velocities and probable cavitation characteristics for assumed depths - would be 8-pole and 16-pole using 50Hz power (estimated four and two knots for AKULA). If the drive motors are squirrel-cage induction design with slip-rates of about one-half of one-percent - typical for motor rated at about 400 hp, the actual operating speeds will be about 746 and 373 rpm.

The section of the BOREY outer hull that is opened outward to deploy these thrusters measures 9.5 feet (2.9m) in length and 4.9 feet (1.5m) vertically. The forward end of this movable section is located port and starboard 17.2 feet (5.2m) forward of the leading edges of the stern planes where they join the hull and 2.7 feet (0.8m) below the projected plane of the stern planes.

The diameter of the thruster shroud is about three feet (0.9m). The length appears to be at least eight feet (2.4m). The thruster propellers turn within a circle with a diameter very slightly less than three feet (0.9m), and are four-bladed.

Above information from open sources.