CODAG

CODAG, short for Combined Diesel And Gas, is a ship propulsion arrangement that uses both diesel engines and a gas turbine to drive a single propeller shaft through a combining gearbox with clutches. In this system, diesels provide economical propulsion at low to moderate speeds, while the gas turbine supplies additional shaft power for high-speed operation. The combining gearbox and clutches allow the prime movers to be engaged separately or together, enabling different operating modes without changing the propeller gear ratios.

Typical modes include diesel-only for efficient cruising, gas turbine-only for high-speed bursts, and full CODAG operation where both diesel engines and the gas turbine contribute to propulsion. Some installations also enable a smooth transition between modes to improve acceleration and maneuverability. The arrangement relies on a carefully engineered gearbox to match the torque and speed of the diverse power sources to the propeller shaft.

CODAG is contrasted with CODLAG and CODOG. CODLAG uses diesel-electric generation and a gas turbine driving the propeller through electric motors, offering smoother power management but adding electrical complexity. CODOG employs either diesel or gas turbine to drive the shaft, but not both simultaneously. CODAG aims to combine the efficiency of diesels with the high-power capability of a gas turbine, at the expense of increased mechanical complexity and maintenance requirements. It has been used on a range of naval and civilian vessels where flexible, high-performance propulsion is advantageous.