An officer on duty on a fishing vessel was watching a drift net or long-line going a-drift after it had beeh set. Whenever, if he can estimate the relative position of the ship in relation to her fishing gear during drifting without recurring to an object (flag, light, reflector, radio buoy), he can employ the method to watch the gear effectively. For example, the authors made the experiment with the drifting of the Oshoro-Maru, a fishery training ship of Hokkaido University, in the Bering Sea, and tried to express the direction and distance of the drift by parameters with the ship's head and wind velocity.The experiment 1. The corner reflector connected to the drift net was selected as the datum point of the experiment. In this case, the reflector was allowed to drift together with the ship according to currents and waves, but it felt no effect from the wind in spite of the movement of the ship. 2. The observers on the ship measured the distance and the bearing of the reflector by radar every 30 minutes and calculated the drifting by solving the triangls. Observations were made several hours each day for 14 days. The results are as follows: 1. The relation between the wind velocity (W) and the drift is shown in Fig. 2. 2. The relation between drifting coefficient (K) and the ship's head (α) is shown in Fig. 3. Accordingly, the drifting velocity (U) is expressed by the following equation, U=(a-bα)√<S/Sw>W. 3 .The direction of drifting is closely related to the ship's head (shown in Fig. 8), accordingly, the drifting direction (β) is expressed by the following general equation, β=a+bα, and the coefficients a and b are based upon the ships' drifting characteristics. 4. Consequently, if one knows the drifting characteristics of his own ship, he can estimate the position to which the ship has drifted.
