Combined gas or gas (COGOG) is a

propulsion Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived from ...

system for

ship A ship is a large watercraft, vessel that travels the world's oceans and other Waterway, navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally disti ...

s using

gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...

engines.

System

A high efficiency, low output turbine is used for cruising speeds with a high output turbine being used for high-speed operations. A

clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...

allows either turbine to be selected, but there is no

gearbox A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded Renault) which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/r ...

to allow operation of both turbines at once. This has the advantage of not requiring heavy, expensive and potentially unreliable gearboxes. The reason that a smaller turbine is used for cruising is that a small turbine running at 100% power is more fuel efficient than a bigger turbine running at 50% power. The system is currently used in the 2 ships of the

Russian Navy The Russian Navy is the Navy, naval arm of the Russian Armed Forces. It has existed in various forms since 1696. Its present iteration was formed in January 1992 when it succeeded the Navy of the Commonwealth of Independent States (which had i ...

's s, the

Japanese Maritime Self-Defense Force The , abbreviated , also simply known as the Japanese Navy, is the maritime warfare branch of the Japan Self-Defense Forces, tasked with the naval defense of Japan. The JMSDF was formed following the dissolution of the Imperial Japanese Navy ( ...

Hatsuyuki-class destroyer The is a class of destroyer, serving with the Japan Maritime Self-Defense Force (JMSDF). It was the first class of first generation of general-purpose destroyers of the JMSDF. Background Destroyers of the JMSDF had been divided into two series, ...

s, and the

Royal Netherlands Navy The Royal Netherlands Navy (, ) is the Navy, maritime service branch of the Netherlands Armed Forces. It traces its history to 8 January 1488, making it the List of navies, third-oldest navy in the world. During the 17th and early 18th centurie ...

s (on which the

Greek Navy The Hellenic Navy (HN; , abbreviated ΠΝ) is the naval force of Greece, part of the Hellenic Armed Forces. The modern Greek navy historically hails from the naval forces of various Aegean Islands, which fought in the Greek War of Independence ...

s are based). It was formerly used in the

Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...

Type 42 destroyer The Type 42 or ''Sheffield'' class was a class of fourteen guided-missile destroyers that served in the Royal Navy.Marriott, Leo: ''Royal Navy Destroyers since 1945'', , Ian Allan Ltd, 1989 A further two ships of this class were built for and ...

and

Type 22 frigate The Type 22 frigate also known as the ''Broadsword'' class was a ship class, class of frigates built for the British Royal Navy. Fourteen were built in total, with production divided into three batches. Initially intended to be anti-submarine ...

, as well as the

Royal Canadian Navy The Royal Canadian Navy (RCN; , ''MRC'') is the Navy, naval force of Canada. The navy is one of three environmental commands within the Canadian Armed Forces. As of February 2024, the RCN operates 12 s, 12 s, 4 s, 4 s, 8 s, and several auxiliary ...

's ''Iroquois''-class destroyer.

Development

Having previously pioneered the combined diesel or gas (CODOG) system, in 1968 the Royal Navy converted an old

frigate A frigate () is a type of warship. In different eras, the roles and capabilities of ships classified as frigates have varied. The name frigate in the 17th to early 18th centuries was given to any full-rigged ship built for speed and maneuvera ...

, , to COGOG propulsion as a test bed for use in later ships. Because developing a new gas turbine purely for marine use would be very expensive, it was decided to adapt a

Rolls-Royce Olympus The Rolls-Royce Olympus (originally the Bristol B.E.10 Olympus) was the world's second two- spool axial-flow turbojet aircraft engine design, first run in May 1950 and preceded only by the Pratt & Whitney J57, first-run in January 1950. It i ...

engine, which had been originally designed for the

Avro Vulcan The Avro Vulcan (later Hawker Siddeley Vulcan from July 1963) was a jet-powered, tailless, delta-wing, high-altitude, strategic bomber, which was operated by the Royal Air Force (RAF) from 1956 until 1984. Aircraft manufacturer A.V. Roe ...

bomber and further developed for the

Concorde Concorde () is a retired Anglo-French supersonic airliner jointly developed and manufactured by Sud Aviation and the British Aircraft Corporation (BAC). Studies started in 1954, and France and the United Kingdom signed a treaty establishin ...

supersonic airliner. Cruising power was provided by two

Rolls-Royce Proteus The Bristol Proteus was the Bristol Engine Company's first mass-produced gas turbine engine design, a turboprop that delivered just over 4,000 hp (3,000 kW). The Proteus was a reverse-flow gas turbine. Because the second turbine dro ...

gas turbines, originally designed for

turboprop A turboprop is a Gas turbine, gas turbine engine that drives an aircraft Propeller (aeronautics), propeller. A turboprop consists of an intake, reduction drive, reduction gearbox, gas compressor, compressor, combustor, turbine, and a propellin ...

airliners, each rated at . The Olympus had to be down-rated to to keep within the limits of the ''Exmouth's'' hull structure. Even before the ''Exmouth'' trials had started, the Royal Navy had already ordered the first class of vessels to be designed from the start for COGOG propulsion, the

Type 21 frigate The Type 21 frigate, or ''Amazon''-class frigate, was a British Royal Navy general-purpose escort that was designed in the late 1960s, built in the 1970s and served throughout the 1980s into the 1990s. Development In the mid-1960s, the Royal Na ...

s, in which the Proteus turbines were replaced by a pair of

Rolls-Royce Tyne The Rolls-Royce RB.109 Tyne is a twin-shaft turboprop engine developed in the mid to late 1950s by Rolls-Royce Limited to a requirement for the Vickers Vanguard airliner. It was first test flown during 1956 in the nose of a modified Avro Linco ...

engines. The Tynes were rated at each, giving a cruising speed , while an Olympus rated at 25,000 shp gave a maximum speed of . However, they were beaten into service by the Canadian s, which were powered by two

Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of RTX Corporation (formerly Raytheon Technologies). Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially ...

FT4A2 gas turbines creating and two Pratt & Whitney FT12AH3 cruising gas turbines creating , giving a maximum speed of .

Disadvantages

The operation of large gas turbines on ships produces a high volume of very hot exhaust gasses, which can hinder onboard helicopter operations, and also greatly increases a ship's

infrared signature Infrared signature, as used by defense scientists and the military, is the appearance of objects to infrared sensors. An infrared signature depends on many factors, including the shape and size of the object, temperature, and emissivity, reflecti ...

making it more conspicuous to enemy sensors and guided weapons. The ducting and filters required take up a considerable amount of space in a ship, and the volume of air being drawn in can exacerbate an internal fire. This was found to be a factor in the loss of during the 1982

Falklands War The Falklands War () was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British Overseas Territories, British dependent territories in the South Atlantic: the Falkland Islands and Falkland Islands Dependenci ...

. Many navies have now abandoned pure gas turbine propulsion in favour of

combined diesel–electric and gas Combined diesel–electric and gas (CODLAG) is a modification of the combined diesel and gas propulsion system for ships. A variant, called the combined diesel–electric or gas (CODLOG) system, contains the same basic elements but will not allo ...

(CODLAG) systems.Marriott 1990, pp. 148–149

References

{{DEFAULTSORT:Combined Gas Or Gas Marine propulsion