風圧に依る船の横漂流を考慮した鮪延繩漁具監視法(日本航海学会第36回講演会)

Abstract

In thse observations the direction and the velocity of ships drifting by wind action with engines at a stop were calculated by taking the bearings of the big flag at the end of tuna long lineby means of the gyrocompass of the ship and by taking its elevation (vertical angle) by the sextant and so measuring the distance. The following are the results according to the drifting observations made at 151 spots by the Taisei-maru while practising in tuna fishing in the Pacific Ocean of 01°〜15°N., 97°〜100°W. from March to May and from October to November in 1965. (1) As for the Taisei-maru the velocity of drifting is approximately proportional to that of the wind. (2) The ship is apt to drift catching the wind 1〜2 points before the beam. (3) The central direction of drifting is 15°〜20° ahead from the direction in which the wind blows away. The stronger the wind blows, the more remarkable this tendency becomes. If the velocity of the wind is more than 7.5〜10.0m/sec, the ship does not drift astern any more. (4) The best way of watching the tuna long line is thus to sail on setting it to the weather side catching the wind about 2 points from the bow on the lee board in case of drifting and then to drift with the bow turned toward the direction where the fishing implement is stretched. In this way we can easily find the long line after we have drifted beyond its end and even lost sight of it because we must necessarily meet with the implement if we sail into the wind from there.