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 that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguishe ...

s using

gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...

engines. 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 engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts ...

allows either turbine to be selected, but there is no

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), diffe ...

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's s, the Japanese Maritime Self-Defense Force's Hatsuyuki-class destroyers, and the Royal Netherlands Navy s (on which the

Greek Navy The Hellenic Navy (HN; el, Πολεμικό Ναυτικό, Polemikó Naftikó, War Navy, 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 var ...

s are based). It was formerly used in the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by Kingdom of England, English and Kingdom of Scotland, Scottish kings from the early medieval period, the first major maritime engagements were foug ...

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 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 warfare f ...

, as well as the

Royal Canadian Navy The Royal Canadian Navy (RCN; french: Marine royale canadienne, ''MRC'') is the naval force of Canada. The RCN is one of three environmental commands within the Canadian Armed Forces. As of 2021, the RCN operates 12 frigates, four attack subma ...

's ''Iroquois''-class destroyer.

Development

Having previously pioneered the

combined diesel or gas Combined diesel or gas (CODOG) is a type of propulsion system for ships that need a maximum speed that is considerably faster than their cruise speed, particularly warships like modern frigates or corvettes. For every propeller shaft there is ...

(CODOG) system, in 1968 the Royal Navy converted an old frigate, , 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 is ...

engine, which had been originally designed for the

Avro Vulcan The Avro Vulcan (later Hawker Siddeley Vulcan from July 1963) is 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 an ...

bomber and further developed for the

Concorde The Aérospatiale/BAC Concorde () is a retired Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC). Studies started in 1954, and France and t ...

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 turbine engine that drives an aircraft propeller. A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. ...

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 frigates, 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 Li ...

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 Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military avi ...

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 ( es, link=no, Guerra de las Malvinas) was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British dependent territories in the South Atlantic: the Falkland Islands and its territori ...

. Many navies have now abandoned pure gas turbine propulsion in favour of combined diesel-electric and gas (CODLAG) systems.Marriott 1990, pp. 148-149

References

{{DEFAULTSORT:Combined Gas Or Gas Marine propulsion