Marine propulsion system, control method therefor, and marine vessel

A marine vessel comprising:

• a hull;
• and
• a marine propulsion system comprising:
• first propulsion devices that are steerable and located at a stern of a hull;
• a second propulsion device that is steerable and located at a predetermined position in front of the stern of the hull;
• and
• a controller configured or programmed to:
• obtain a target direction and a required propulsion force when an instruction of a parallel motion is obtained or when it is determined to execute the parallel motion;
• and
• determine a point of action of a resultant force of propulsion forces applied to the hull by the first propulsion devices during execution of the parallel motion based on the target direction and the required propulsion force, control the first propulsion devices to apply the resultant force corresponding to the required propulsion force in the target direction to the point of action determined, and control the second propulsion device to apply a propulsion force to the predetermined position to cancel a veering component and a component in a direction perpendicular to the target direction with respect to the hull due to the resultant force;
• move a position of the point of action backward or increase the propulsion forces of the first propulsion devices as the required propulsion force increases during the execution of the parallel motion;
• and
• increase the propulsion force of at least one of the first propulsion devices applying the propulsion force including a component in a forward direction as the required propulsion force increases when the position of the point of action reaches a rear limit position and the propulsion force of at least one of the first propulsion devices applying the propulsion force including a component in a backward direction reaches an upper limit propulsion force generatable during the execution of the parallel motion.

A control method for a marine propulsion system including first propulsion devices that are steerable and located at a stern of a hull and a second propulsion device that is steerable and located at a predetermined position in front of the stern of the hull, the control method comprising:

• obtaining a target direction and a required propulsion force when an instruction of a parallel motion is obtained or when it is determined to execute the parallel motion;
• determining a point of action of a resultant force of propulsion forces applied to the hull by the first propulsion devices during execution of the parallel motion based on the target direction and the required propulsion force obtained;
• controlling the first propulsion devices to apply the resultant force corresponding to the required propulsion force in the target direction to the point of action;
• controlling the second propulsion device to apply a propulsion force to the predetermined position to cancel a veering component and a component in a direction perpendicular to the target direction with respect to the hull due to the resultant force;
• moving a position of the point of action backward or increasing the propulsion forces of the first propulsion devices as the required propulsion force increases during the execution of the parallel motion;
• and
• increasing the propulsion force of at least one of the first propulsion devices applying the propulsion force including a component in a forward direction as the required propulsion force increases when the position of the point of action reaches a rear limit position and the propulsion force of at least one of the first propulsion devices applying the propulsion force including a component in a backward direction reaches an upper limit propulsion force generatable during the execution of the parallel motion.