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By Bruce Rule - October 27, 2013


The following Russian website provides information about the loss of the YANKEE Class Soviet SSBN K-219 on 6 October 1986 while the unit was on patrol southeast of Bermuda:"

The following paragraph from that site describes the propulsion mode employed by the YANKEE at the time of the missile tube explosion: the initial event in a cascade of events that resulted in the loss of the submarine.

(Quote) Thirty days into its deployment, K-219 maneuvered into her assigned water in the Sargasso Sea. The boat came to periscope depth at 0456 on 3 October for the regular broadcast and after five minutes began to dive to 85 meters. Conditions at that moment were the following: the main power plant was operating in single eschelon mode, the starboard reactor was operating at 30 percent while the port reactor was scrammed (shut down) with all the dampers and the steam generator and turbine in a ready state; the starboard turbine was turning the screw while the port shaft was hooked up to the emergency electrogenerator. (end quote)


The purpose of operating on one reactor was to accumulate an equal number of full-power hours on each reactor operating separately and thus extend the period between overhaul cycles that required refueling of the reactors. Note: this is the most parsimonious (Occum-approved) and; hence, most logical explanation of single reactor operations. Other, convoluted explanations - which strained credibility when proposed - may be dismissed.

The wording is obscure; however, hooking the port shaft to the “emergency electrogenerator” could have been a procedure to permit operation of that shaft – when declutched from its reduction gear - by a battery-powered, shaft-mounted motor in case the starboard reactor scrammed, i.e, to provide an immediately available low speed emergency propulsion mode if the starboard reactor scrammed.

This line-up could have another advantage if the declutched port shaft is minimally powered by the emergency electrogenerator while the primary propulsion load is on the starboard shaft. If the declutched port shaft is allowed to “windmill” (freely rotate in the flow), it would operate at about 45 percent of the speed of the driven shaft; however, it would still create drag and effectively reduce the speed of the submarine. The turns-per-knot (TPK) value of a submarine operating on one shaft with the other shaft windmilling is about 1.25 times the TPK value when both shafts are powered. If the declutched shaft is electrically powered up to about 70 percent of the speed of the driven shaft, the drag will be significantly reduced. This “electrically-assisted” propulsion mode would usually be employed by diesel submarines with two or three shaft lines; however, there is no reason why it could not be used by twin-shaft nuclear submarines if the above described emergency electrogenerator mode is available. This mode would also reduce broadband acoustic energy produced by a windmilling propeller by reducing flow discontinuities (turbulence) from that propeller.

Also note there is no “free lunch” in terms of maximum shaft speeds that are possible when twin-shaft submarines operate on a single shaft. Because of the extra load thrown on the powered shaft by single shaft operations, the speed of the powered shaft should not exceed 75-80 percent of maximum rpm possible during operation on both shafts.

The above information, and much of the content of other postings provided by the writer, either already have been or should be archived under ARTICLES because it is unlikely it will otherwise be available if needed by active duty System personnel who, hopefully, access this site. As previously stated, half a century in this business has taught the writer that it is not possible to know enough; one can only try to assimilate all information plausibly associated with “our business” because today's seemingly obscure fact may be tomorrow's Rosetta Stone.

A classic example of the value of such apparently incidental information occurred at ONI many years ago when those responsible for assessing foreign marine propulsion system developments learned the Soviets were using “deadwood” main propulsion shaft line bearings. They were flummoxed by the use of this term until informed that ship's bearing surfaces could be - and had been for centuries - made from Lignum Vitae (Latin for Tree of Life), a very dense (heavy) tropical wood that, when heated by the rotation of a propeller shaft, exudes, even after decades, an oil ideal for lubrication. Lignum Vitae is so heavy that it will not float; hence, the term “deadwood.” provides the following statements:

“Known for centuries, as the most “steel friendly” industrial bearing material Lignum-Vitae is arguably the oldest & most valuable bearing in the history of man. Lignum Vitae bearings outlast competitive bearings six to one, lasting over 60 years without the need for costly repetitive service and replacement.”

“The aft main shaft strut bearings for USS Nautilus (SSN-571), the world's first nuclear powered submarine, were composed of this wood.” Source: Wikipedia.