Effects of Wind and Wave on a Ship's Course and Speed

Abstract

To analyze the effects of wind and wave upon a ship's speed and course is a very important problem from the view point of navigation. The authors experimented them aboard the Oshoro Maru (1181 G/T) in the Bering Sea. The experiment 1. The ship's courses were given 12 directions every 30°in regard to the direction of the wind. 2. The corner reflector connected to the salmon gill-net was selected as the datum point of experimentation. In this case, the reflector was allowed to drift equally with the ship by ocean currents and drift currents, but felt no effect from the wind. 3. As shown in Fig.1, the observers on the ship measured the distance and bearing of the reflector by radar at observation points A & B, and calculated the direction and distance of the ship's run through the water. And by the same way they repeated such observations on the 12 courses every day. 4. Sailing time of one course was planned to be 10 minutes. The result 1. Relation between the direction of wind wave and ship's speed We divided the data into three groups according to weather conditions and showed them in Fig.2, and as mean values, formed smooth curves, following approximately the cosine curve. 2. Relation between the direction of wind wave and the steering error The error of steering is gotten as the difference between the planned course set in the gyro auto pilot and the mean value of course recorded by the course recorder, as shown in Fig.3, in connection with wind directions. As shown in this figure, the ship's course drifted to the right regardless of wind wave directions. 3. Relation between the direction of wind and lee way The lee way corresponding to each wind direction is shown in Fig.4 in relation to wind velocities. The coefficient of the lee way must be considered with some allowance from the view point of the number and deviation of data, however under usual sailing and weather conditions it is to be desired that navigators deal with the lee way with equal care as compared with the steering error, accuracies of estimated ocean currents, drift currents and tidal currents.