A joystick outputs an operating signal indicating a tilt amount and a twist direction of the joystick. A controller receives the operating signal and controls a marine propulsion device to output a thrust having a magnitude depending on the tilt amount. The controller changes a rudder angle of the marine propulsion device such that a watercraft turns in a direction corresponding to the twist direction. The controller reduces a speed of changing the rudder angle with an increase in the magnitude of the thrust.