The assessment of maneuverability of a ship is very important from the view point of safety of human beings and of pollution of ocean. And, it is quite natural that every ship yard wants to have some tools with which they can build a ship with good maneuverability. But, maneuvarability of a ship is very subtle problem, and to calculate the exact maneuvering motion, lots of captive model tests must be carried out. Futhermore, in the initial design stage we can not make the scale model, because the lines of a ship is not fixed. In this paper, some approximate method to calculate the maneuvering motion of a ship, with the principal dimensions of hull, and propeller, rudder characteristics only, is studied. And, proposed approximate method is used to calculate the turning and zig-zag maneuver of several ships. The results of those calculations and the usability of the method are discussed.