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Potential Acoustic Vulnerability of BOREY and YASEN Class Russian Nuclear Submarines

By Bruce Rule - Jul 14, 2016

Russ: please archive.

As previously posted this site, both BOREY and YASEN Class Russian nuclear submarines use a hybrid propulsion system: the GTZA OK-9VM geared turbine system for speeds above circa eight knots and the 5,550 hp PG-141M dc motor for lower speeds to avoid the acoustic vulnerabilities associated with the geared-turbine drive originally designed in the very late 1970s for use with AKULA, SIERRA, OSCAR and TYPHOON Class Soviet nuclear submarines.

Also previously discussed: (1) the second flight of BOREY SSBNs will use GTZA OK-9VM geared-turbine systems recovered from scrapped OSCAR units, and (2) the GTZA OK-9VM cannot be secured during use of the PG-141M turbo-electric propulsion mode because of heating/deformation problems associated with the sudden acceleration of a “cold” turbine.

In addition to previously discussed acoustic vulnerability issues (transients) associated with very low-speed operation of the GTZA OK-9VM system, two other potential vulnerabilities may occur: (1) turbine blade-rate sources (turbine rotational rate times the number of blades in each stage of the turbine) and hobbing errors created by the relatively crude gear-cutting machines used to fabricate the OSCAR and AKULA double-reduction planetary gear systems.

See linked site ( for discussions of planetary gear system cutting/finishing technologies not available when AKULA/OSCAR systems were fabricated.

The writer leaves it to active duty analysts to determine the most probable numbers for turbine blade (vane) values and hobbing error components and their probable frequencies based on the assumed operating speed of the GTZA OK-9VM system during turbo-electric mode operations.