In a moving center estimation method, a provisional moving center is set at a predetermined position in a neighborhood of an actual moving center of a hull. A sample thrust having a predetermined magnitude and direction is applied to the provisional moving center by driving the outboard motor, and a magnitude and direction of an angular acceleration generated in the hull by application of the sample thrust is detected. The magnitude of the angular acceleration is compared with a predetermined threshold value, and a position of the provisional moving center is changed and set so that the angular acceleration may converge in the threshold value, when the angular acceleration is larger than the threshold value.