(Istitute for Sea-training) The yawing motion, lying to single anchor, is a hard problem, but we, navigators must know how it is. The other hand, on the practical experience of vessel at sea, there are many difficulties in the way of success, if the practical experience had failed, we would have the total loss of vessel and destructive of dear life. And there, we tested it by model ship of T.S. Hokuto-maru (1/100 scale), for one step to practical experience of vessel, and obtained the following result ; 1) Relation between yawing motion and cable tension, 2) Autlines of yawing motion.