CODLAG

CODLAG, or Combined Diesel Electric And Gas, is a marine propulsion arrangement that combines diesel-electric propulsion with a gas turbine to drive a ship’s propellers. In CODLAG, the gas turbine is used to generate electrical power, which feeds propulsion motors that turn the propeller shafts. There is no direct mechanical link between the gas turbine and the propeller, allowing the turbine to run at its optimal speed while the propeller operates at its own optimal speed.

Configuration and operation: A bank of diesel engines drives generators to supply electrical power for ship systems and propulsion. A gas turbine also drives a generator to provide additional electrical power, particularly at higher speeds. The propulsion motors connected to the propeller shafts are fed by these electrical sources and typically drive the propellers through a geared transmission. A power management system coordinates load sharing, enabling smooth transitions between diesel-only, gas-turbine-only, and combined operation to achieve the desired speed and efficiency.

Advantages and limitations: CODLAG offers flexible performance over a wide speed range, potential reductions in acoustic signature at low speeds, and redundancy through multiple independent power sources. The electric-drive arrangement allows simpler mechanical propulsion gear compared with direct-drive turbine systems and can improve maneuverability and throttle response. However, the system is electrically complex, requires space for multiple gensets and switchgear, and can incur higher initial costs and maintenance.

Applications: CODLAG has been adopted on various modern naval vessels, including mid-sized frigates and other warships in Europe, where fuel efficiency, quiet operation, and flexible power management are valued. It is one of several electric-propulsion options used in contemporary naval architecture.