Combined gas and steam

Large (land-based) electric powerplants built using this combined cycle can reach conversion efficiencies of over 60%.

[1] If the turbines do not drive a propeller shaft directly and instead a turbo-electric transmission is used, the system is known as COGES (combined gas turbine-electric and steam).

Especially COGAS should not be confused with Combined steam and gas (COSAG) power plants, which employ traditional, oil-fired boilers for steam turbine propulsion for normal cruising, and supplement this with gas turbines for faster reaction times and higher dash speed.

E.g. Celebrity Cruises' Millennium and other ships of her class use turbo-electric plants with two General Electric LM2500+ gas turbines and one steam-turbine.

This uses the waste heat of combustion from the exhaust and turns it into steam to produce torque which is input into the crankshaft.