A Summary of BOREY and YASEN Class Submarine Characteristics Derived from Open Sources
By Bruce Rule - Jun 14, 2014
A SUMMARY OF BOREY AND YASEN CLASS RUSSIAN SUBMARINE CHARACTERISTICS DERIVED FROM OPEN SOURCES
This article expands upon discussions of the Russian submarine project 955, the BOREY Class SSBN, previously posted on this site on 8 March 2014 as "A Prediction About the BOREY Class Russian Ballistic Missile Submarine (SSBN)."
Additional information from open sources further supports that prediction - now, in the writer's opinion, upgraded to an assessment - that the BOREY, to reduce noise produced by main propulsion system reduction gears, has a hybrid propulsion system:turbo-electric (TE) for low speeds and turbine-reduction (TR) for speeds above about eight knots. Additionally, this article discusses one explanation for the BOREY use of a pump-jet propulsor while the Project 885 YASEN Russian SSGN (NATO: GRANEY) has an “open” skewed, seven-bladed screw.
Impacted by the severe fiscal constraints imposed on new Russian nuclear submarine construction programs by the disintegration of the Soviet Union, Rubin Bureau designers of the BOREY Class SSBN, working in building 55 at the Northern Machine Enterprise in Severdovinsk (1), used propulsion system and pressure-hull components from canceled Project 971 AKULA Class SSN hulls to complete the first two BOREY hulls. (2) To a lesser extent, the same approach may have been used with the YASEN Class SSGN. As such the BOREY and YASEN Class can better be described as generation 3.5 Russian nuclear submarines rather than fourth generation.
As discussed in the posting of 8 March, the BOREY and Project 971 AKULA Class SSN both use the GTZA OK-9VM main turbine gear assembly. That TR system is now known to include a "planetary double-reduction" gear. (1) The same source also states the BOREY has an “electric propulsion” (TE) capability which, as previously discussed, is provided by a 5,500 hp dc motor, probably the PG-141, also used as the main propulsion motor by all variants of the KILO Class Soviet/Russian diesel submarine (SS).
It is probable all third-generation Soviet/Russian nuclear submarines with main propulsion power train horsepower ratings of about 50,000 per shaft use the GTZA OK-9VM system with the same two-stage planetary reduction gear. This assessment includes the AKULA and SIERRA SSNs, the OSCAR SSGN and - yes - even the TYPHOON SSBN; however, none of these classes have a TE capability. Such standardization was - and remains - a typical Soviet/Russian design practice for nuclear submarine main propulsion power trains.
Use of the OK-9VM system was extended to the BOREY which the Russians are calling a fourth generation nuclear submarine. Apparently the use of an existing power train was the result of “catastrophic under-funding” (1) which existed within the Russian ship-building industry in 1997 when the BOREY was, in a cost-cutting measure, radically redesigned from a twin power train concept to a single-shaft design that used the bow and stern sections of the canceled (dismantled) Project 971 AKULA Class SSNs. (2) For this reason, at least the first two BOREYs have eight torpedo tubes: four 650mm and four 533mm, a “heavy” weapons capability for an SSBN.
Specifically, the lead BOREY unit, the YURIY DOLGORUKIY (Russian hull designation K-535) used sections from the cancelled AKULA “KOUGAR” (K-337) while the second BOREY, the ALEXANDR NEVESKIY (K-550), used sections of the canceled AKULA “LYNX” (K-333). (2)
К-337 «Кугуар» 836 18.08.1992 Не достраивалась, корпус использован для постройки К-535 «Юрий Долгорукий» проекта 955
К-333 «Рысь» 837 31.08.1993 Не достраивалась, корпус использован для постройки К-550 «Александр Невский» проекта 955А
DISCUSSIONS OF LOW-SPEED PLANETARY GEAR SYSTEM NOISE PROBLEMS
Planetary gear systems have approximately two-thirds the weight and half the volume of locked-train, double-reduction gear systems that transmit the same horsepower; however, planetary systems can have low-speed acoustic vulnerabilities not characteristic of locked-train systems which, as discussed below, is one explanation for the assessed Russian use of a low-speed TE capability in the BOREY, an SSBN that will operate primarily at low-speeds.
The power input to simple planetary gear systems is usually directly from main propulsion turbine to the sun-gear with the output from the planet carrier or yoke which directly drives the screw in a single-stage system. In two-stage (double reduction) systems, such the GTZA OK-9VM, the output of the first stage is the input to the second-stage.
At relatively high rotational speeds, the planets are held against the ring-gear by centrifugal force; however, the increased space that then exists between the planets and the sun-gear (in systems not machined to high tolerances) allows more impact noise (tooth-slap) to occur.
At very low rotational speeds, for which reduced centrifugal force exists, the planets, because of gravity, will fall away from the ring-gear when they pass through the upper arc of the circle of rotation, and will fall toward the sun-gear. Thus, at low rotational speeds, which are low ship's speeds, less precisely machined planetary gears can produce impact energy from both tooth-slap and the positional changes – no matter how small – of the planets relative to the ring- and sun-gears. Thus, planetary gear systems can produce more noise at the very low-speeds typical of SSBN patrols than at higher speeds.
In this context, the need a low-speed TE propulsion mode for BOREY Class SSBNs becomes evident. This appears to be yet another case of “Better is the enemy of good enough” with “Better” being the reduction of low-speed acoustic issues by the design and fabrication of a high-tolerance planetary gear system and “good enough” being development of a low-speed TE propulsion capability that solves the noise problem by simply not operating the planetary gear at those speeds. The Russians appear, again, to have taken the ”good enough” - and less costly - approach.
DISCUSSION OF THE BOREY PUMP-JET PROPULSOR
The BOREY pump-jet propulsor, like the AKULA conventional screw, is driven by a left (port)-turning shaft. An advantage of a pump-jet propulsor is that the stator directs thrust developed by the rotor along the axis of the submarine which reduces the tangential thrust which, in turn, reduces torque on the hull which allows the stern area control surfaces to be smaller than would be the case with a conventional screw. This permitted the BOREY to use the stern section of the much smaller Project 971 AKULA Class SSN. Consistent with this commonality assessment, within measurement error, the span (maximum width) of both the BOREY and AKULA stern planes is 45 feet; however, that value represents only eight percent of the overall length of the BOREY but 12 percent of the length of the AKULA.
This may be the primary reason why the BOREY has a pump-jet propulsor and the new YASEN (NATO: GRANEY) Class Project 885 Russian SSGN has a conventional (open) skewed seven-bladed screw. (3) (It may something for others to verify and think about that the span of the YASEN stern planes is about 57 feet or almost 15 percent of its length.)
The shape of a pump-jet "shroud" (decreasing internal diameter fore to aft) accelerates the in-flow to the rotor thereby increasing pressure which raises the speed at which cavitation will occur: the inception threshold. The acoustic down-side of a pump-jet is that such systems produce two forcing frequencies: a rotor (blade)-rate component at the rotational rate of the propeller shaft times the number of blades on the rotor ((see source (4) for extensive discussions of submarine blade-rate)), and a stator-rate component at the rotational-rate of the propeller shaft times the number of vanes on the stator. Although the stator, by design, is stationary, it has rotational velocity (at the speed of the shaft) relative to the rotor and thus radiates an acoustic component.
The number of rotor blades and stator vanes in a pump-jet system are usually different prime numbers. For example, the pump-jet on the UK Mark 50 torpedo has 11 blades on the rotor and 13 vanes on the stator. The pump-jet on the Project 877V KILO Class – the “ALROSA” - has an 11-bladed rotor and a seven-vaned stator. (8) Schematic data indicates the BOREY stator may - repeat may - have 11 vanes.
The acoustic problem associated with pump-jets occurs where multiples of the forcing frequencies of a rotor and stator coincide and reenforcement occurs. If, for example, a pump-jet system has a seven-bladed rotor and an 11-vaned stator, multiples (specific harmonics) of the rotor-rate and the stator-rate will coincide at 11 times the rotor-rate (77 times the system shaft-rate) which also is seven times the stator-rate (77 times the shaft-rate). If the number of rotor-blades of a pump-jet system is known, the number of vanes on the stator can be determined based on the signal strength of higher-order multiples (harmonics) of the rotor source. If the rotor blade configuration is unknown, it may still be possible to determine both the rotor and stator configurations by working through the prime number options for integer combinations consistent with observed harmonic structure of the rotor-rate source.
DISCUSSIONS OF THE BOREY MAXIMUM SUBMERGED SPEED AND TURNS-PER-KNOT (TPK) VALUE
The original USS SCORPION (SSN 589) hull was cut in half and a 128-foot missile section inserted to create the USS GEORGE WASHINGTON (SSBN 598). The overall length was increased by 51-percent, from 252-feet to 380-feet. At the same maximum shaft rpm and with the same developed shaft horsepower, the maximum speed was reduced by 24-percent and the TPK value increased by 33-percent.
With the exception of the design of the sail, the BOREY SSBN is essentially an AKULA SSN lengthened by 53-percent (364-feet to 558-feet) but with the same 50,000 shaft horsepower GTZA OK-9VM main propulsion power train and the same bow and stern sections as the AKULA.
Numerous open-sources, including (2), list the maximum AKULA speed as 33 knots with one source (3) refining that value to 33.3 knots. If, like the 589/598 example above, the maximum submerged speed of the BOREY is reduced by 24-percent from the AKULA value of 33 knots, the result will be about 25 knots and the BOREY TPK value will be about 33-percent higher than the AKULA TPK value at moderate to high speeds. At speeds below 10 knots - and especially at missile patrol speeds - this relationship will "decay" because pump-jets are not as efficient at low speeds as conventional screws.
To achieve the 29-knot speed capability listed by several Internet sources (2, 3), the BOREY would require about 80,000 shaft horsepower or 30,000 more than the listed capability of the GTZA OK-9VM power train.
If the Russians had developed a new main turbine gear assembly for the YASEN Class SSGN, it probably would also have been used by BOREY Class SSBN; however, since units of the BOREY Class use the GTZA OK-9VM power train, it is probable the YASEN Class also uses that system. If the YASEN does use the GTZA OK-9VM system and has the 31-knot speed capability listed by sources (2, 3), the YASEN TPK value should be about eight-percent higher than the AKULA value.
Source (5) provides the following information on the YASEN SSGN.
(Quote) Now (Aug 2012), according to reports in business daily Kommersant and official mouthpiece Izvestia, the latest sea trial indicates the (YASEN) sub likely will not be ready until summer of 2013. One of the problems, according to an anonymous source cited by Interfax, is that the reactor not only doesn’t deliver enough power for the vessel, but that the vessel’s operation is also noisy – something undesirable in the stealth mode in which submarines are to operate. (end quote)
It is suggested the reported noise problems are what could be expected if the YASEN uses a GTZA OK-9VM main turbine gear assembly (with a planetary gear) that had been stored in an uncontrolled environment since 1993 when construction of lead ship of the class, the SEVERODVINSK (K-560), began at the Severmash shipyard in Severodvinsk on the White Sea in Arctic Russia where the average mean temperature for the Dec through Feb period in nine degrees (F).
SUBMARINE GEAR NOISE: NOT A NEW PROBLEM
The Naval Engineers Journal, states that as far back as World War II, the issue of reduction gear noise (internal and external) led to the decision to remove gears from US diesel submarines and substitute large electric motors.(6) In contrast, both shaft lines of the German Type XXI SS used a single-stage gear between the engine and the propeller shaft with a reduction ratio of 1.620 (79/128), and another single-stage gear between the electric motor and the propeller shaft with a reduction ratio of 5.077 (39/198) (7)
DISCUSSIONS OF THE BOREY THRUSTER SYSTEM
As discussed in the posting of 8 March, the BOREY has two maneuvering thrusters located well aft in closeable “tunnels” between the outer “light” hull and the pressure hull. These thrusters are driven by two-speed PG-160 motors rated at 410 hp each. Use of the term “two-speed” indicates the system employs ac motors with the different speeds achieved by changing the effective motor-pole configurations. Considering the use of these thrusters for low-speed maneuvering, the most probable configurations would be 8-pole and 16-pole, respectively 750 and 375 rpm with a 50 Hz power source. If the drive motors are squirrel-cage induction design with slip-rates of slightly less than one-percent, the actual operating speeds of the thrusters will be about 745 and 372 rpm.
These relatively high operating speeds are a result of design requirements that accommodate the relationship of motor speed and hp rating to size: the slower the speed, the larger the motor with the same hp rating. This relationship was the compelling reason for assessing Project 636 KILO submarines use a star-design planetary reduction gear with a ratio of about 2:1 to lower the maximum propeller shaft rpm for 636 units to 250 rpm from the 500 rpm maximum for the older Project 877 KILOs while still using the 5,500 hp PG-141 main propulsion motor on both projects. (A dc motor that develops 5,500 hp rating at 250 rpm would have about twice the 380 cubic foot volume of a PG-141 motor which develops the same hp at 500 rpm.)
Speeds of two-knots and four-knots are reasonable assumptions for a two-speed BOREY thruster system designed primarily for in-port (pier-side) maneuvering. The rpm and type of mounting of these thrusters indicate it is unlikely they can be operated quietly.
Conjecture that the BOREY thrusters could be the "electric propulsion" referred to by (1) is discounted because source (9) states the BOREY has a 5,500 hp (4.1 mW) motor. That motor is the source of propulsion power for the TE mode using the pump-jet propulsor which probably is driven by a single-stage reduction gear with a ratio of about six to one. Such a motor-to-shaft reduction gear system would be significantly smaller than the main propulsion planetary reduction gear and would be easier to quiet.
9. http://www.nti.org/media/pdfs/project_955_borey_1.pdf?_=1341964661&_=1341964661 ;