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]
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 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]