四片式中层拖网主要部件尺寸变化对其性能的影响

THE EFFECT OF THE CHANGE OF SIZE OF THE MAIN PARTS OF FOUR PANEL MID WATER TRAWL ON ITS CHARACTERISTICS

通过拖网系列模型水池试验，研究四片式中层拖网网衣主要部件尺寸变化对网具性能的影响。试验结果表明：（１）因侧网宽度变化对扫海面积影响的规律是侧网宽度越小，扫海面积越大；在拖速３．５～５．０ｋｎｏｔ的范围内，侧网与背（腹）网之比为０．７１４时，网口垂直扩张最大。（２）在网袖长度与网具全长之比为１３．２５８％～３０．９３６％范围内，扫海面积随着网袖长度的增长而增大；当其比值大于３０．９３６％以后，扫海面积随着网袖长度的增长而减小。网袖长度对网具阻力影响的趋势是网袖长度越长网具阻力越大。（３）网身长度与网口拉直长度之比为２５．５５％时，网口垂直扩张最佳。

The 960.000m×226.275m(107.800m) mid water trawl, widely used in China for Alaska pollack fishing in the North Pacific in the 90's,was selected as the target net in model testing through which to research the effect of the width of side panel as well as the length of wings and body on the performance of four panel mid water trawls. The results were as follows: (1) With the other conditions unchanged, side panel width has obvious impact on the vertical opening of four panel trawls. In the towing speed of 3.5 to 5.0knot net A 2, in which L f/L d (L f the side panel width, L d belly panel width) was 0.714, got the greatest vertical opening. When towing speed increased to 5.5knot and more, net A 3 with L f/L d of 0.846 reached the top value of vertical opening. If the L f/L d value went to the range above 1.0, the vertical opening decreased with the increase of L f/L d. It was found in the model testing that the smaller the side panel width was the greater the sweeping section area would be. (2) At lower towing speed, shorter wings would result in higher vertical opening of net mouth. When trawling speed went above 4.5knot, net B 2 of 17. 678% in L s/L a (L s stretched lenth of wing, L a stretched lenth of full net) obtained the highest vertical opening value. When L s/L a was smaller than 30.936% the sweeping section area increased with extention of wing while in the condition of L s/L a above 30.936%, the sweeping area was reversely proportional to the L s/L a value. At all towing speed, drag force increased when wings lengthened. (3) When the L b/C (L b body length, C stretched circumference of fore part of body) value was 25.554%, the highest vertical opening of net mouth was reached. The change rate of vertical opening at different speed resulted from the change of body length were directly proportional to the towing speed. As to the changes of energy consumption coefficient for net towing and that of vertical opening with horizontal opening unchanged, the trends were basically the same.