扩张帆布对大型中层拖网性能的影响

针对我国引进的大型中层拖网所使用的扩张帆布，通过拖网模型试验，设计了三种面积和三种不同冲角的扩张帆布调整试验，并比较了使用扩张帆布与使用塑料浮子对网具性能的影响。结果表明：网口拉紧长度1040m，网口网目为a=20m六角形网目的大型中层拖网，使用长度为100m手纲、长度为48m叉纲、重锤重量为320kg×2、下袖端间距68．4m时，在帆布面积调整试验中，当冲角前纲长度为17．2m，冲角后纲长度为17．6m，拖速为2．57m·s^-1条件下，使用5．0m^2的扩张帆布比4．0m^2网口高度可提高11．92％，网具阻力上升6．74％，能耗系数下降6．5％。在冲角调整试验中，使用5．0m^2的扩张帆布，当冲角后纲的长度固定为17．6m，冲角前纲的长度从17．2m缩短为16．4m时，网口高度下降26．36％，网具阻力下降11．22％，能耗系数上升24．1％。大型中层拖网使用扩张帆布比使用塑料浮子在不同的拖速下网口高度变化幅度小，在高拖速时，有网口高、能耗系数低的优势，但在拖速低于2．06m·s^-1时，网口垂直扩张和能耗系数没有优势。试验的长宽比为20的扩张帆布的升力系数Cy可达1．16左右。

Effects of net-mouth opening device made of canvas on large pelagic trawl

Net-mouth opening device made of canvas has been used in large-mesh pelagic trawl in China. Through trawl net model test in flume tank, three different canvas areas and three different attack angles of horizontal expansion canvas were selected and the performance of the expansion canvas and plastic floats were analyzed. The results showed that： in the canvas area adjustment test, when the attack angle of front line was 17.2 m, the angle of back line was 17.6 m, the trawling speed was 2.57 m/s, the net mouth of 5.0 m^2 expansion canvas was 11.92% higher than that of 4.0 m^2 expansion canvas, and net resistance increased 6.74% ,and the coefficient of energy consumption decreased by 6.5%. In the angle adjustment test, using 5.0 m^2 expansion canvas, when back line was 17.6 m and front line adjusted from 17.2 m to 16.4 m, the net mouth height decreased by 26.36%, the net resistance decreased by 11.22%, and the coefficient of energy consumption increased by 24.1%. The net mouth height of expansion canvas changed smaller than those of plastic floats at different speeds. And using expansion canvas in high trawling speed, the height of net mouth tended to be higher, and coefficient of energy consumption was lower, but when trawling speed was lower than 2.06 m · s^ -1, the height of net mouth and coefficient of energy consumption were similar to those of plastic floats. When attack angle of front line decreased to 16.4 m, the angle of Gang fixed length was 17.6 m, and the angle of the length of the Gang reduced from 17.2 m to 16.4 m, network port height decreased by 26.36%, the net resistance decreased by 11.22%, and energy consumption coefficient increased by 24.1%. Through trawl net model test in flume tank, lift coefficient （Cy） of the canvas could reach about 1.16.