System for and method of controlling watercraft

1. A system for controlling a watercraft, the system comprising:

a marine propulsion device rotatable about a steering shaft;

a steering actuator to rotate the marine propulsion device about the steering shaft;

a position sensor to detect a present position of the watercraft;

a direction sensor to detect a present direction of the watercraft; and

a controller configured or programmed to:

control the marine propulsion device and the steering actuator such that the watercraft moves along a target course;

determine a target direction of the watercraft based on the target course;

calculate a directional difference between the target direction and the present direction;

determine a target yaw rate based on the directional difference with reference to target yaw rate data defining a relationship between the directional difference and the target yaw rate;

change a rudder angle of the marine propulsion device by controlling the steering actuator based on the target yaw rate;

determine which of rightward turning and leftward turning is being made by the watercraft;

impose a limitation on a leftward target yaw rate when the rightward turning is being made by the watercraft; and

impose a limitation on a rightward target yaw rate when the leftward turning is being made by the watercraft.

2. The system according to claim 1 , wherein the controller is further configured or programmed to:

determine a plurality of target points located on the target course;

determine a plurality of sections each set between adjacent two of the plurality of target points;

determine which of a post-right turning section and a post-left turning section is being followed by the watercraft in the plurality of sections;

impose a limitation on the leftward target yaw rate when the post-rightward turning section is being followed by the watercraft; and

impose a limitation on the rightward target yaw rate when the post-leftward turning section is being followed by the watercraft.

3. The system according to claim 1 , wherein the target course has a zigzag shape.

4. The system according to claim 1 , wherein the target course has a spiral shape.

5. A method of controlling a watercraft including a marine propulsion device, the method comprising:

determining a target course of the watercraft;

detecting a present position of the watercraft;

detecting a present direction of the watercraft;

determining a target direction of the watercraft based on the target course;

calculating a directional difference between the target direction and the present direction;

determining a target yaw rate based on the directional difference with reference to target yaw rate data defining a relationship between the directional difference and the target yaw rate;

changing a rudder angle of the marine propulsion device based on the target yaw rate;

determining which of rightward turning and leftward turning is being made by the watercraft;

imposing a limitation on a leftward target yaw rate when the rightward turning is being made by the watercraft; and

imposing a limitation on a rightward target yaw rate when the leftward turning is being made by the watercraft.

6. The method according to claim 5 , further comprising:

determining a plurality of target points located on the target course;

determining a plurality of sections each set between adjacent two of the plurality of target points;

determining which of a post-right turning section and a post-left turning section is being followed by the watercraft in the plurality of sections;

imposing a limitation on the leftward target yaw rate when the post-rightward turning section is being followed by the watercraft; and

imposing a limitation on the rightward target yaw rate when the post-leftward turning section is being followed by the watercraft.

7. The method according to claim 5 , wherein the target course has a zigzag shape.

8. The method according to claim 5 , wherein the target course has a spiral shape.