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 one diesel engine for cruising speed and one geared gas turbine for high speed dashes. Both are connected to the shaft with clutches, only one system is driving the ship in contrast to CODAG-systems, which can use the combined power output of both. The advantage of CODOG is a simpler gearing compared to CODAG but it needs either more powerful or additional gas turbines to achieve the same maximum power output. The disadvantage of CODOG is that the fuel consumption at high speed is poor compared to CODAG.

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Wikipedia