CONTROL METHOD AND CONTROLLER OF MARINE ENGINE

Object: To efficiently switch the operation mode from the fuel saving mode and the ordinary mode to improve the fuel efficiency, while maintaining the ship maneuverability. Means to Realize Object: A controller (4) receives a set rotation rate and an actual rotation rate. In an ordinary mode, a PID controlling apparatus (12) computes an output value to be supplied to fuel supply means of a ship engine (2) from the difference between the set rotation rate and the actual rotation rate in the ordinary mode. The PID controlling apparatus (12) also has a fuel saving mode in which the width of change per unit time of the output value is smaller than in the ordinary mode. Detecting units (20, 22, 24, 26, 28) for monitoring variations in the set and actual rotation rates are provided. The PID controlling apparatus (12) is switched to the ordinary mode when the set rotation rate or the actual rotation rate goes out of a predetermined range in the fuel saving mode.