This article discusses the experience of the US Navy with Synchro-Self-Shifting (SSS) clutches. The US Navy has nearly 40 years of experience using SSS clutches in main reduction gears of gas-turbine-driven ships and propulsion systems with combinations of gas turbines and diesel engines or electric motors, and in steam-turbine propulsion plants for use with electric motor drives. Over 900 SSS clutches have been installed in 14 different classes of US Navy ships, with some having been in service for over 30 years. SSS clutches have accumulated approximately 15,278,000 hours of operation. Mean Time Between Failures in Hours for US Navy clutch applications is relatively high (271,550 hours) based on the operational hours accumulated and the total number of failures that have occurred. The maintenance and repair strategy used for US Navy SSS clutches is similar to a Performance Based Logistics arrangement, where the Navy maintains a rotatable pool of ready-for-issue clutches, and in the event of a problem or failure, the clutch is changed out with an available spare.

A unique Reverse Reduction Gear system is being utilized on the U.S. NAVY AOE-6 Class ships. The AOE-6 is the first of (4) Fast Combat Support ships being built by National Steel and Shipbuilding Company (NASSCO) in San Diego, Ca. The principal characteristics of the AOE-6 Class ships are as follows: Length Overall - 753 Feet 8.5 Inches Beam - 107 Feet Mean Draft (Full Load) - 37 Feet 10 Inches Displacement - 48,500 Long Tons Total Shaft Horsepower - 100,000 HP The ships are powered by (4) General Electric LM2500 gas turbine engines, driving thru (2) main reduction gears manufactured by the Cincinnati Gear Co., to (2) shafts fitted with fixed pitch propellers. Each main reduction gear utilizes (2) SSS-TOSI Reversible Coupling Converters (RCC’s) to provide reversing and slow speed maneuvering capability for each propulsion shaft. The RCC is a fluid coupling/torque converter that has (26) insertable stator vanes positioned around the periphery of the rotor circuit. These stator vanes, when inserted, reverse fluid flow inside the RCC, and consequently reverse the direction of rotation of the RCC output (turbine) rotor. The RCC was tested extensively by the Naval Surface Warfare Center (formerly NAVSSES) in Philadelphia, Pa. This paper provides an overview of the RCC design and operating principles; highlights of the prior testing accomplished; and an informative brief that details the successful integration, operation, and performance of the RCC aboard these new U.S. Naval vessels.

The U.S. Navy has nearly forty years of experience using SSS (Synchro-Self-Shifting) Clutches in main reduction gears of gas-turbine-driven ships and propulsion systems with combinations of gas turbines and diesel engines or electric motors, and in steam-turbine propulsion plants for use with electric motor drives. Over 900 SSS Clutches have been installed in fourteen different classes of U.S. Navy ships, some in service for over thirty years. This paper presents a brief overview of the principle SSS Clutch design features and the operating experience in naval propulsion systems worldwide, including operation in various propulsion plants such as controllable reversible pitch (CRP) propellers, fixed-pitch propellers (FPP), etc. The paper will also focus on SSS Clutch designs for specific U.S. Navy applications and installations, U.S. Navy experience, and design changes and improvements that have been implemented since the initial U.S. Navy use of SSS Clutches. Detailed metric (statistical) data, used by the U.S. Navy to evaluate equipment performance and life cycle costs, such as mean time between failure (MTBF), mean time to repair (MTTR), mean logistics delay time (MLDT), and operational availability (Ao) will be used to support experience. In-service experience and failure modes will also be explained as well as findings from the evaluation of clutches that have been subjected to extreme operation/incidents such as overspeed, overtorque, high shock blast, and flood damage. The final part of the paper will discuss current/future applications on U.S. Navy vessels such as the LHD-8, LCS and others; and how the design/features of those SSS Clutch designs will satisfy the operational, reliability, and maintainability requirements established for each ship platform. The metrics and lessons learned will be shown to be equally applicable to clutches for critical auxiliary drive applications such as naval gas turbine generator starting and naval steam turbine generator turning gear systems and how these metrics and lessons learned are being applied for current and future U.S. Navy ship systems.