Turning circle

A turning circle is the path the ship’s pivot point traces in a steady turn at constant rudder, the primary measure of turning ability. The standard trial applies 35 degree rudder, or the maximum permissible, from a steady approach at the test speed to both port and starboard. Key geometry is the advance, the distance gained along the original course at 90 degrees of heading change, the transfer perpendicular to it, and the tactical diameter, the lateral distance at 180 degrees of heading change. IMO Resolution MSC.137(76) limits advance to 4.5 ship lengths and tactical diameter to 5 lengths.