It has been well known that there is an incompatibleness between the course keeping quality and the turing ability of ships, i. e., it will be impossible to improve the course keeping quality of a ship without spoiling her turning ability unless the rudder area is incleased drastically. In this paper, the authors show a method of overcoming this incompatibleness by means of automatic control of helm angle. It is shown that an automatic control of helm angle proportional to the angular velocity as well as the angular acceleration of a ship will result in an effective change in the ship's stability derivatives, and that it is possible then to make a ship more stable on course. Therefore, it will be possible to design a ship originally to have good turning ability with poor course keeping quality consequently, then apply the automatic control so that the ship becomes effectively to have good course keeping quality with rather poor turning ability. In this way, one can switch the ship's maneuverability in dual way according to the circumstance, i. e., when a better course keeping quality is required, the automatic control will be applied superposed with the manual control to make the ship more stable on course, and when a better turning ability is required, the automatic control will be cut off so that the ship can turn more efficiently.