Draft:SSS Gears

S.S.S. GEARS Ltd.

Industry	Engineering
Founded	01.06.1950
Headquarters	Sunbury-On-Thames
Products	SSS Clutch
Website	sssgears.co.uk

SSS Gears is an engineering company which manufactures the SSS (Synchro-Self-Shifting) Clutch, a mechanical freewheel device that can connect and disconnect machines in a drivetrain and is capable of transmitting high torque and operating at high speeds. The SSS Clutch is used in naval propulsion, power generation, process and auxiliary industries. The company is based in Sunbury-on-Thames with a sister company SSS Clutch Inc in Delaware. The company is privately owned and the majority shareholder is the Harold Sinclair Trust, which is an Employee Benefit Trust.

SSS Clutch

The SSS Gears as a company only makes one product – the SSS Clutch, that is an automatic overrunning clutch that connects rotating shafts when the speed of the input shaft matches the speed of the output shaft. The mechanical design transmits power and torque through gear teeth making the SSS Clutch inherently strong and explains why SSS Clutches are mostly used in demanding and high-power applications like Marine Propulsion, Power Generation, large Industrial drives and on applications where reliability and longevity of life are a key design and operational consideration. The UK MOD has designated the SSS Clutch a “Fit and Forget” component after more than 30 years service on the Type 23 Frigates. The US Navy has independently rated the SSS Clutch to exceed 270,000 hours minimum time between failures (MTBF). SSS Clutches have also demonstrated over 50 years of service life in Power Generation applications e.g in Sweden as part of the Svenska Kraftnat Disturbance Reserve.

Invention

The SSS Clutch was originally designed for an automatic car gearbox and invented by Dr Norton Legge, with a patent published in 1931. In 1936 Mr Harold Sinclair, a director of the Fluidrive Engineering Co Ltd, acquired the patents after seeing a prototype exhibited at the London Motor Show. The initial designs of the SSS Clutch transmitted around 250kW for industrial drives (fans, pumps and compressors). They also developed the SSS Powerflow Gearbox to be used within diesel powered shunting locomotives, which were manufactured under licence by Bostock and Bramley for companies like Hunslett Engine Company and Hudswell Clarke.

Harold Sinclair left Fluidrive Engineering along with his Chief Gear Designer, Mr Arthur Clements, and set up a new company that eventually became SSS Gears. The company was originally based in Lion House, Richmond UK, but moved to Acton in the 1960’s and to its current site in Sunbury-on-Thames in 1978. SSS Gears expanded during the 1960’s and 1970’s as Gas Turbines were increasingly used for Marine Propulsion and Power Generation applications.

Marine propulsion

The SSS Clutch was developed for new applications like Motor Gunboat (MGB) 2009, the first vessel to be propelled at sea by a Gas Turbine, and when problems occurred with friction clutches on the Y100 Naval Propulsion System, SSS Clutches were used on HMS Scarborough (F63) Type 12 Frigate and HMS Keppel (F85) Type 14 Frigate (8) as an alternative to friction clutches. After their use in the Y100, SSS Clutches were specified for the Royal Navy Tribal-class frigates and County-class destroyers.

HMCS Bras dOr (FHE 400) the Canadian Navy advanced hydrofoil, used SSS Clutches in its propulsion drive achieving a speed of 63 knots during trials in 1969, making it one of the world’s fastest warships.

Following the Y100, SSS Clutches were adopted on the propulsion drive for  HMS Exmouth (F84), the World’s first all gas turbine warship, and the British Royal Navy Type 21 Frigate, Type 22 Frigate, Type 23 Frigate, Type 42 Destroyer, and on the Invincible-class aircraft carriers HMS Invincible (R05) , HMS Illustrious (R06) and HMS Ark Royal (R07).

During the 1970’s and 1980’s, SSS Clutches were fitted in the US Navy propulsion drive on the Oliver Hazard Perry-class (FFG-7) frigates and retrofitted into the Spruance-class destroyers (DD-963) Ashville-class gunboats (PGM-84) and the US Coast Guard Hamilton-class cutters to replace other types of clutches .

In 1983 the Italian Aircraft Carrier Giuseppe Garibaldi was launched with a Franco Tossi Reversable Converter-Coupling Drive and a direct drive SSS Clutch for continuous ahead propulsion. The same SSS-Tosi reversing drive arrangement was adopted by the US Navy Supply-Class fast combat support ships (AOE-6).

SSS Clutches have been fitted into the propulsion system of gas turbine powered US Navy Warships going forward including the Arleigh Burke-class destroyers (DDG-51) from 1986 onwards and the Constellation-class frigates (FFG-62) from 2022 onwards.

Power generation

In 1963 a 3MW SSS Clutch was installed at the Bristol Siddeley site with a Bristol Proteus Engine for Peaking Power and as a Synchronous condenser providing reactive power for electrical grid support. In 1964, the Central Electricity Generating Board in the UK went on to install Rolls-Royce Avon and Rolls-Royce Olympus gas turbine power generation sets with 30MW and 70MW SSS Clutches for the same application at its Lister Drive, Earley, Croydon B and Rye House sites.

In 1976 SSS designed and manufactured high power clutches for the first utility-scale Compressed-air energy storage (CAES) plant at the Huntorf site in Germany and in 1989 for the McIntosh site in Alabama, which improved efficiency by recovering and reusing heat from the compressors.

The 1^st single-shaft combined-cycle power plant with an SSS Clutch was installed in 1972 at Saarbrucken in Germany. This power plant configuration was deployed more widely through the 1990s with the 100^th plant being built in 1999 at the Midlothian Plant in Texas USA as part of a project for 4 x GT24 ABB gas turbines. SSS has supplied over 500 clutches for this application as of 2025.

The system format is typically Gas Turbine > Electric Generator > SSS Clutch > Steam Turbine on a single-shaft. The SSS Clutch allows the gas turbine to start independently of the steam turbine, which allows for faster start up times, more generation flexibility and a smaller footprint compared to a multi-shaft design. The highest power SSS Clutches for this application were supplied to Jawa Satu Power Plant in 2020 and rated at 400MW .

SSS Clutches are used in Cogeneration Combined Heat and Power (CHP) plants enabling more efficient production of heat and power.

Many countries have committed to net-zero emissions and are adding renewable energy sources like wind power and solar power to decarbonise the generation of electricity. Renewable energy sources reduce CO₂ production and global warming, but do not produce power all of the time due to dark periods of low wind (Dunkelflaute) requiring other sources of dispatchable generation such as energy storage or gas turbine engines. Renewable inverter-based resource can also cause problems with electrical grid stability and system strength. The SSS Clutch enables a power plant to deliver intermittent dispatchable generation and when not delivering power, the generator can operate as a synchronous condenser providing inertia, fault current, voltage control and reactive power management supporting system strength and grid stability. Recent projects include Townsville and Immingham B.