Abstract
In Japan, average values of rudder areas as fractions of lateral plane area A_R/(L・dm) for the class of ships which length between perpendiculars has 40 meters or so are as follows; tug boars…1/23 fishing vessels…1/35 cargo vessels…1/46 Tokyo University of Mercantile Marine has replaced recently its training and experimental ship which it had used since 1952. This ship. "Shioji Moru II" has her values of A_R/(L・dm) of 1/38.4, and of Lpp of 37.0 meters. After maneuverability tests, it is found that she is directionally unstable, and they have fitted a fin to her stern for the compensation. Author reports here the results of Spiral Tests, the effectiveness of the fin, and propose the lower limit value of A_R/(L・dm) for the same class ships.
