Studies on the Midwater Trawl I : Distribution of flow-speed inside the Net and Performance of the Net-shape

This paper described about the basic experiment of on the continuous midwater trawl which was carried out in the experimental circular tank with two types of model net (the one rigged with cone and the other without cone), and with two kinds of webbing (thin twined one and thick twined one); measurement being carried out on the four stages of flow-speed (approximately 1.5, 2, 2.5, 3, kn), using Kanomax flow-meter (constant temperature type, hot film flow-meter), and flow-line-shaped meter-rod. The results obtained are as follows: 1. Even when the trawl was rigged with cone and suction-hose little deformation in trawls was noted. Decreasing percentage in the areas of net moth, horizontal section, and vertical section was observed to be only a little. 2. Concerning the flow-speed, it was generally lower inside the net, than it was outside the net, but an acceleration in flow-speed was recognized in some case. 3．In case of thin twined webbing, net-performance was lower than in the thick one, especially when the flow-speed was low, because there was less extension than in the latter case. Hence the necessity of choosing the twine-size and mesh-size most appropriate to the towing-speed