The speed of the marine engine is controlled by an instrument known as governor, which can be of – hydraulic, electro-hydraulic or electronic governor type.
The most famous types of governor used for both main engine and generator engine is the electro-hydraulic type marine governor. It’s because of this little instrument that the engine speed can be smoothly controlled from a remote space (bridge or engine control room).
The different components of a governor allows for a steady state speed control, along with achieving the required variation in the load.
Know different parts and their function in the governor- http://bit.ly/2F321ag