Studies on the Midwater Trawl II : Model experiments on the Hanging-coefficent, Netshape and Towing-net-resistance

In this paper the authors deal with the model experiments of 6 kinds of four-panelled midwater trawl-nets which were same in constructions, but different in hanging-coefficent. The measurements on the net-shape and towing-net-resistance were carried out in the circuler tank, with about 51 cm/sec of flow-speed. The results obtained are as follows: 1. The net-shape was noted to be different in each net, especially in both the A-net (2% of hanging-coefficent) and the B-net (5% of hanging-coefficent), the cod-end was observed to be fairly expanded. 2. The maximum cross-section-area of net-mouth was obtained in the D-net (15% of hanging-coefficent). 3. Concerning the total towing-net-resistance, the minimum value was showed by the C-net (10% of hanging-coefficent), the maximum by A-net (of the largest mesh number) and the value next to maximum was showed by the F-net (30% of hanging-coefficent; the smallest mesh number). Accordingly, we can assume that, the total net-resistance of bag-net is depending more upon net-shape than upon mesh number of the netting, except those of low hanging-coefficent