Tactical diameter

The tactical diameter of a ship is the distance:
 * travelled on sea surface
 * during a turning circle test
 * with maximum rudder angle
 * by the center of gravity of a ship
 * taken perpendicular to the initial track followed at approach speed
 * when the heading has changed by 180°

The ratio of the tactical diameter divided by the ship's length between perpendiculars gives a dimensionless parameter which can be used to compare ships maneuverability.