Combined gas and gas

Combined gas turbine and gas turbine (COGAG) is a type of propulsion system for ships using two gas turbines connected to a single propeller shaft. A gearbox and clutches allow either of the turbines to drive the shaft or both of them combined. Marine usage of COGAG systems are similar to those found ashore.^[1]

Principle of a COGAG propulsion system

Description

Combined marine propulsion
CODOG CODAG CODLAD CODLAG CODAD COSAG COGOG COGAG COGAS CONAS IEP or IFEP

A COGAG system consists of two gas turbines, each connected to a reduction gearbox. These are each attached to a coupling with both connected to larger gearbox and then to the ship's propeller.^[2]

Advantages and disadvantages

Advantages of the system include a large degree of automation along with quick startup time, they are easier to silence and protect from shock.^[3] Compared to combined diesel and gas (CODAG) or combined diesel or gas (CODOG), COGAG systems have a smaller footprint but a much lower fuel efficiency at cruise speed and for CODAG systems it is also somewhat lower for high speed dashes.^[4] Issues with COGAG systems include their complexity and gearbox issues and high fuel use.^[5]

List of COGAG ships

• Kolkata-class guided-missile destroyer (Indian Navy)
• INS Vikrant (aircraft carrier) (Indian Navy)
• Type 22 frigate (Batch 3) (Royal Navy)
• Invincible-class aircraft carrier (Royal Navy)
• Cavour-class aircraft carrier (Italian Navy)
• Asagiri-class destroyer (Japan Maritime Self-Defense Force), and subsequent destroyer classes
• Hyūga-class helicopter destroyer (Japan Maritime Self-Defense Force), helicopter carrier
• Izumo-class helicopter destroyer (Japan Maritime Self-Defense Force), helicopter carrier
• Type 055 destroyer (People's Liberation Army Navy)
• Neustrashimy-class frigate (Russian Navy)
• Sejong the Great-class destroyer (Republic of Korea Navy)
• Skjold-class corvette (Royal Norwegian Navy)
• Arleigh Burke-class destroyer (United States Navy)
• Ticonderoga-class cruiser (United States Navy)

Citations

1. Soares 2015, pp. 10, 27.
2. Plaff 2021, p. 95.
3. Graves & Carleton 1963, p. 12.
4. Soares 2015, p. 31.
5. Plaff 2021, p. 92.

References

• Graves, G. L.; Carleton, R. S. (September 1963). "Gas Turbines for Unconventional Craft". Bureau of Ships Journal. 12 (9): 7–12.
• Plaff, Manfred (2021). Ship Operation Technology: Reference Book and Guidebook. Wiesbaden, Germany: Springer Fachmedien. ISBN 978-3-658-32729-3.
• Soares, Claire (2015) [2008]. Gas Turbines: A Handbook of Air, Land and Sea Applications (Second ed.). Kidlington, Oxford: Elsevier. ISBN 978-0-12-410461-7.