What is the smallest displacement at which combined diesel and gas propulsion is efficient and affordable?
Short answerAbout 2,500 tons is suggested as the lower threshold. Affordability remains relative, and the carrier examples challenge any simple upper size limit.
NotesAbout 2,500 tons is suggested as the point where a ship can begin to justify both diesel and gas-turbine machinery. Below that size, the advice is to choose diesel for range or gas turbines for speed. Affordability remains relative to the navy and its requirements. One proposed upper boundary favors gas-turbine electric machinery in larger ships, with the turbines held near their most efficient operating settings. The Queen Elizabeth-class carriers immediately challenge that simple division because a very large carrier can also combine diesel and gas machinery.