Constant ship speed control method

Claim 1

A method for controlling the speed of a ship which includes a main engine for driving a main shaft at a given rpm, a fuel rack adapted to be positioned for setting the horsepower generated by the main engine, a controllable pitch propeller having a variable blade angle connected to the main shaft, and a ship speed detector, said method comprising the steps of: determining the actual horsepower of the main engine in accordance with the main engine fuel rack position and the main shaft rpm; determining a desired horsepower corresponding to a desired ship speed in accordance with the detected ship speed from the ship speed detector, the actual horsepower of the main engine, and a preset ship speed; generating a first function of first fuel rack position and first main shaft rpm which provides an optimum propeller efficiency in accordance with said preset ship speed and generating a second function of a second fuel rack position and a second main shaft rpm; comparing said first and second functions so as to define a range related to said second function where use of said first function results in a rich torque and a second range where use of said first function results in no rich torque, thereby generating a minimum fuel characteristic function; determining a desired engine rpm in accordance with said minimum fuel characteristic function and said desired horsepower; controlling the rpm of the main shaft in accordance with said desired rpm; determining a desired fuel rack position in accordance with the desired rpm and said desired horsepower; comparing said desired fuel rack position and the main engine fuel rack position to obtain a difference therebetween; and controlling the blade angle of the controllable pitch propeller in accordance with said difference thereby to attain efficiency in operation.

Claim 2

A method for controlling the speed of a ship which includes a main engine for driving a main shaft at a given rpm, a fuel rack adapted to be positioned for setting the horsepower generated by the main engine, a controllable pitch propeller having a variable blade angle connected to the main shaft, and a ship speed detector, said method comprising the steps of: determining the actual horsepower of the main engine in accordance with the main engine fuel rack position and the main shaft rpm; determining a desired horsepower corresponding to a desired ship speed in accordance with the detected ship speed from the ship speed detector, the actual horsepower of the main engine, and a preset ship speed; generating a first function of first fuel rack position and first main shaft rpm which provides an optimum propeller efficiency in accordance with said preset ship speed and generating a second function of a second fuel rack position and a second main shaft rpm; comparing said first and second functions so as to define a range related to said second function where use of said first function results in a rich torque and a second range where use of said first function results in no rich torque, thereby generating a minimum fuel characteristic function; determining a desired engine rpm in accordance with said minimum fuel characteristic function and said desired horsepower; controlling the rpm of the main shaft in accordance with said desired rpm; determining a desired fuel rack position in accordance with the desired rpm and said desired horsepower; comparing said desired fuel rack position and the main engine fuel rack position to obtain a difference therebetween; and controlling the blade angle of the controllable pitch propeller in accordance with said difference thereby to attain efficiency in operation.