Abstract
It it often said that the position of the pivoting point of any ship moves to the stem along with the progress of its turning motion, or that it moves with the ship's situation in the course of its turning motion.
But when an ordinary ship is steered in a calm sea without external forces, her pivoting point is fixed, and settled regardless of her speed or rudder angle.
So any ship has her own proper turning quality which depends on the position of her pivoting point at any given time. If we divide the turning quality of this ship into two kinds, that is, the steering and the rotating, each has also a special quality of its own. So these qualities of any ship can be shown by indices which are comparable with those of other ships.
