トロール網の研究 : 3種のトロール網の模型実験

To obtain some fundamental suggestions on the gear efficiency of the three different types of trawl net, the authors carried out the model experiment, and compared them with each other, basing on the physical characteristics of the net. The first is the two-seam-net was used in 1950's in East China Sea; the second is the four-seam-net was used in 1960's in Bering Sea; the third is the six-seam-net was used on board of the "Nansei Maru". These three nets aimed for catching the demersal fishes. The results obtained in this study are summarized as follows: (1) The towing speed, when the height of net mouth is stable, differs in each net. The towing speed is about 2.3 knot on the two-seam-net, about 2.6 knot on the four-seam-net and about 3.0 knot on the six-seam-net. On ordinary towing condition, the height of net mouth on the four-seam-net is the highest, marking about 6.0-9.0 percent of the maximum breadth of the net, among the three types of trawl net. (2) Net resistance is explained by general equation R=k V^<n>, and the values (n), the highest values observable in the four-seam-net, marking 1.64-1.99, the second is the values of two-seam-net, marking 1.42-1.64, and the third is those of six-seam-net, marking 1.32-1.53