Drift when an Anti-Rolling Tank is in Operation and Suspension due to Wind Action

Abstract

When a ship rolls because of waves, it drifts. After experimentations Prof. Suehiro and others reported that the drift caused by heavy rolling is greater than that caused by smooth rolling. The authors have experimented with the drifting of ships for several years on a rough ocean, but according to our studies, the drifting is not greater when the waves are larger and less great when the waves are smaller if the wind velocity is the same. In this paper, we compared the driftings when an anti-rolling tank was being used and when it was not. The method 1. This experiment was carried out on the Hokusei-maru (273 G/T) a fishery training ship of Hokkaido University, in the North Pacific Ocean. 2. The corner reflector which was connected to the salmon-gill net was selected as the datum point of 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. 3. Observers on the ship measured the distance and the bearing of the reflector by radar every 30 minutes and calculated the drift by solving the triangle. The anti-rolling tank was used on and off every 30 minutes alternately. The observations were made for several hours each day for 11 day. The results 1. As shown in Fig.1 the ship drifts almost the same whether it rolls a lot or a little. (here: wind velocity was less than 11m/sec) 2. The relation between the wind velocity and the drift is shown in Fig. 2(a) and (b). 3. The direction of drifting is closely related to the ship's head (shown in Fig.5), and the drifting distance can be calculated from the wind velocity. Consequently, if one knows the drifting characteristics of his own ship, he can estimate the position to which the ship has drifted.