System for and method of controlling watercraft

A method of controlling a watercraft including a first marine propulsion device and a second marine propulsion device, the first marine propulsion device being rotatable about a first steering shaft, the second marine propulsion device being rotatable about a second steering shaft, the method comprising:

• receiving an operating signal from an operator manually operable to output the operating signal indicating a desired motion of the watercraft;
• determining a first target rudder angle of the first marine propulsion device, a second target rudder angle of the second marine propulsion device, and a target thrust ratio in accordance with the operating signal and controlling the first marine propulsion device and the second marine propulsion device based on the first target rudder angle, the second target rudder angle, and the target thrust ratio such that the watercraft performs the desired motion, the target thrust ratio being a ratio of magnitude between a first thrust generated by the first marine propulsion device and a second thrust generated by the second marine propulsion device;
• retrieving a first default angle for the first target rudder angle, a second default angle for the second target rudder angle, and a default thrust ratio for the target thrust ratio, the first default angle, the second default angle, and the default thrust ratio being preliminarily set such that a net thrust of the first thrust and the second thrust is oriented straight sideways and extends from a center of gravity of the watercraft;
• when the desired motion is straight sideways movement, controlling the first marine propulsion device and the second marine propulsion device to start moving the watercraft by setting the first default angle, the second default angle, and the default thrust ratio as the first target rudder angle, the second target rudder angle, and the target thrust ratio respectively;
• detecting an error between the straight sideways movement of the watercraft and an actual motion of the watercraft;
• determining at least one of a first correcting angle, a second correcting angle, and a correcting thrust ratio so as to reduce the error;
• correcting the first target rudder angle, the second target rudder angle, and the target thrust ratio with the first correcting angle, the second correcting angle, and the correcting thrust ratio respectively;
• and
• repeatedly detecting the error and repeatedly updating the first correcting angle, the second correcting angle, and the correcting thrust ratio.

A system for controlling a watercraft, the system comprising:

• a first marine propulsion device rotatable about a first steering shaft;
• a second marine propulsion device rotatable about a second steering shaft;
• an operator manually operable to output an operating signal indicating a desired motion of the watercraft;
• and
• a controller configured or programmed to:
• determine a first target rudder angle of the first marine propulsion device, a second target rudder angle of the second marine propulsion device, a first target thrust indicating a target magnitude of a first thrust generated by the first marine propulsion device, and a second target thrust indicating a target magnitude of a second thrust generated by the second marine propulsion device in accordance with the operating signal;
• control the first marine propulsion device and the second marine propulsion device based on the first target rudder angle, the second target rudder angle, the first target thrust, and the second target thrust such that the watercraft performs the desired motion;
• store a first default angle for the first target rudder angle and a second default angle for the second target rudder angle, the first default angle and the second default angle being preliminarily set such that a net thrust of the first thrust and the second thrust is oriented straight sideways and extends from a center of gravity of the watercraft;
• when the desired motion is straight sideways movement, control the first marine propulsion device and the second marine propulsion device to start moving the watercraft by setting the first default angle and the second default angle as the first target rudder angle and the second target rudder angle respectively;
• detect an error between the straight sideways movement of the watercraft and an actual motion of the watercraft;
• determine at least one of a first correcting angle, a second correcting angle, a first correcting thrust, and a second correcting thrust so as to reduce the error;
• correct the first target rudder angle, the second target rudder angle, the first target thrust, and the second target thrust with the first correcting angle, the second correcting angle, the first correcting thrust, and the second correcting thrust respectively;
• and
• repeatedly detect the error and repeatedly update the first correcting angle, the second correcting angle, the first correcting thrust, and the second correcting thrust in accordance with the error.