四片式中层拖网主要部件尺寸变化对其性能的影响

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密度越小，扫海面积越大，在拖速３．５￣５．０ｋｎｏｔ的范围内，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．

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

The 960. 000m @ 226. 275m( 107. 800m) mid-water t raw l, widely used in China for Alaska pollack fishing in the North Pacif ic in the 90. s, w as selected as the target net in model test ing through w hich to research the effect of the w idth of side-panel as w ell as the length of w ings and body on the performance of four-panel mid-w ater t raw ls. The result s w ere as follows: ( 1) With the other condit ions unchanged, side-panel w idth has obvious impact on the vert ical opening of four-panel t raw ls. In the tow ing speed of 3. 5 to 5. 0knot net A2, in w hich Lf/ Ld( Lf - the side-panel w idth, Ld-belly-panel width) w as 0. 714, got the greatest vertical opening. When tow ing speed increased to 5. 5knot and more, net A3 w ith Lf/ Ld of 0. 846 reached the top value of vert ical opening . If the Lf / Ld value w ent to the rang e above 1. 0, the vert ical opening decreased w ith the increase of Lf / Ld. It w as found in the model test ing that the smaller the side-panel w idth w as the greater the sw eeping sect ion area would be. ( 2) At low er tow ing speed, shorter w ings w ould result in hig her vert ical opening of net mouth. When t raw ling speed went above 4. 5knot , net B2 of 17. 678% in Ls / La ( Ls-stretched lenth of w ing, La-st retched lenth of full net) obtained the highest vert ical opening value. When Ls/ La w as smaller than 30. 936% the sw eeping sect ion area increased with extention of w ing w hile in the condit ion of Ls/ La above 30. 936% , the sw eeping area w as reversely proport ional to the Ls/ La value. At all tow ing speed, drag force increased w hen w ings leng thened. ( 3 ) When the Lb/ C ( Lb-body leng th, C-st retched circumference of fore part of body ) value w as 25. 554%, the hig hest vert ical opening of net mouth was reached. The change rate of vertical opening at different speed resulted f rom the change of body length w ere directly proport ional to the tow ing speed. As to the changes of energ y consumption coef ficient for net tow ing and that of vertical opening w ith horizontal opening unchanged, the t rends w ere basically the same.