Capabilities of the Russian Nuclear Submarine Hybrid Propulsion System
By Bruce Rule - Oct 29, 2015
A Russian source quoted in the writer's posting of 27 Oct 2015 confirms use of a hybrid propulsion system ((turbo-electric (TE) for slow speeds, and turbine-reduction (TR) for higher speeds)) by the BOREY Class SSBN and the YASEN (NATO: GRANEY) Class SSN. Data exists from which the maximum speed capabilities of the TE mode – described by the Russians as “regime stalk” - the regime being the US - can be assessed for these classes.
When the original USS SCORPION hull was cut in half on the construction way and a 128-foot missile bay was inserted to create the USS GEORGE WASHINGTON (SSBN-598), the overall length was increased by 51-percent and the maximum submerged speed – using the same shaft horsepower (shp) - was reduced by 23-percent.
The BOREY Class Russian SSBN is essentially an AKULA Class Russian SSN lengthened by about 43-percent. Numerous open sources provide a maximum submerged speed for the AKULA of 33-knots. If the same reduction of speed with increased length known for the US platforms applies to the BOREY relative to the AKULA, the maximum submerged speed of the BOREY should be about 28 knots, close to the published Russian value of 29 knots. AKULA, BOREY and YASEN all use the GTZA OK-9VM main propulsion power train rated at 43,000 shp.
As previously posted, the 5,550 horsepower rating (at 500 rpm) of the motor installed on BOREY as the power source for TE mode operations is an exact match for the PG-141 main propulsion dc motor used by all JULIETT, BRAVO, INDIA, BELUGA and KILO Class Soviet/Russian diesel submarines. Additionally, the volume of the “supplementary (power) source” shown by a line drawing of the internal arrangement of compartment eight of the BOREY is approximately the volume of the PG-141: 380 cubic feet.
The mathematical relationship of speed to horsepower (Concepts in Submarine Design; Roy Burcher and Louis J. Rydill, Oct 27 1995) allows published Russian values for the BOREY and YASEN to be used to determine the power required for any other speed, i.e., the entire speed-power curve can be reconstructed.
Although the BOREY – and probably the YASEN - have two ATUs (Automated Turbo-Generator Units), the Russian term for Ship's Service Turbo-Generators: (SSTGs) rated at 3500 kW (4700 hp) each, it is probable that during TE mode operations, the rectified electrical output of only one ATU will power the PG-141 while the other ATU will provide the submarine's electrical requirements; hence, no more than 4700 hp will be available for electrical propulsion. (Such an arrangement would be similar to “single eschelon” operation, the Russian term for operation on one SSTG, as discussed by the CO of YANKEE K-219 lost in Oct 1986 southeast of Bermuda.)
These values and assessments indicate the maximum submerged speed capability of the BOREY Class Russian SSBN in the TE propulsion mode with power provided by a single, fully-loaded ATU will be about 15 knots while the YASEN Class Russian SSN – operating in the TE mode with similar power restrictions – will be about 16 knots. A more probable maximum speed in the TE mode - which would require only half-loading of one 3500 kW (4700 hp) ATU would be 11 knots for the BOREY (2300 hp) and 12 knots for the YASEN (2500 hp).
For those to whom the above numbers appear to be a little out of whack, consider that an additional 580 hp is required to accelerate the YASEN from 11 to 12 knots while an additional 3900 hp is required to add that final knot: from 30 to 31.
Apparently concerned about acoustic detection issues associated with operation of planetary gears at low speeds, the Russians addressed that vulnerability by using a dc motor to provide an alternate propulsion mode with the GTZA OK-9VM turbine-gear assembly “disabled” or “in stand-by” - to use Russian terms.
The purpose of the TE mode is (1) to reduce the acoustic detectability of BOREY Class units when operating at slow speeds while on missile patrols, and (2) to reduce the detectability of YASEN Class units when conducting ASW operations, i.e., reduce the possibility of counter-detection.
See the Comments section of the linked posting for detailed discussions of planetary gear system noise problems at low speeds.