A sailing assisting system for a vessel comprising: a movable controlling device configured to instruct a revolution speed of a propeller included in a propelling system for the vessel; an actuator configured to drive the controlling device; a positional information acquisition unit configured to acquire positional information of a hull to which the propelling system is attached; a determination unit (21C, 21c) configured to determine, based on the positional information and information on a specific water area where sailing is limited, whether the hull stays within the specific water area or whether there is a possibility that the hull enters the specific water area; and a control unit (21E, 21e) configured to control the actuator to limit a movable range of the controlling device if the determination unit (21C, 21c) determines that the hull stays within the specific water area or that there is a possibility that the hull enters the specific water area; the sailing assisting system being characterized in that: the controlling device is further configured to instruct a posture of the propelling system; the controlling device includes a trim angle controlling unit configured to instruct a trim angle of the propelling system as the posture, and if the determination unit (21C, 21c) determines that the hull stays within a shallow water area or a water area with sunken rocks as the specific water area, the control unit (21E, 21e) limits a movable range of the trim angle controlling unit to a range where a contact between the propelling system and a seabed is avoided. a movable controlling device configured to instruct a revolution speed of a propeller included in a propelling system for the vessel; an actuator configured to drive the controlling device; a positional information acquisition unit configured to acquire positional information of a hull to which the propelling system is attached; a determination unit (21C, 21c) configured to determine, based on the positional information and information on a specific water area where sailing is limited, whether the hull stays within the specific water area or whether there is a possibility that the hull enters the specific water area; and a control unit (21E, 21e) configured to control the actuator to limit a movable range of the controlling device if the determination unit (21C, 21c) determines that the hull stays within the specific water area or that there is a possibility that the hull enters the specific water area; the sailing assisting system being characterized in that: the controlling device is further configured to instruct a posture of the propelling system; the controlling device includes a trim angle controlling unit configured to instruct a trim angle of the propelling system as the posture, and if the determination unit (21C, 21c) determines that the hull stays within a shallow water area or a water area with sunken rocks as the specific water area, the control unit (21E, 21e) limits a movable range of the trim angle controlling unit to a range where a contact between the propelling system and a seabed is avoided. the controlling device is further configured to instruct a posture of the propelling system; the controlling device includes a trim angle controlling unit configured to instruct a trim angle of the propelling system as the posture, and if the determination unit (21C, 21c) determines that the hull stays within a shallow water area or a water area with sunken rocks as the specific water area, the control unit (21E, 21e) limits a movable range of the trim angle controlling unit to a range where a contact between the propelling system and a seabed is avoided.