Analysis of the circle test on the actual ship has made it clear that even a low approach speed has influence on the turning circle and that a change in the helm angle tells on the turning circle due to the aspect ratio of the rudder. By making use of these results as well as that of the model test, the Hovgaard-Schoenherr formula was modified, and K3 value was sought with B/d as parameter. In this way the turning circle has come to be estimated very simply.