网袖长度对底层大网目拖网性能的影响

Effects of wing size on the performance of a large mesh bottom trawl

为掌握拖网网袖对大网目底拖网网具性能的影响,本研究针对东海区典型的大网目底拖网（72目×18 m）,设计试验6种纵向拉直长度不同的网袖,分析比较了不同袖长比Lw/L（Lw–网袖纵向拉直长度,L–网具纵向拉直长度）对网具阻力、网口高度和水动力性能的影响。结果表明,（1）随着Lw/L的增大,网具阻力增加,但增加到36.45%之后,阻力几乎不再变化;（2）Lw/L对阻力的影响与拖速有关,速度越大,阻力随Lw/L的变化越大;（3）网口高度随Lw/L的增大而提高,在Lw/L为36.45%~38.69%时达到最佳,随后降低;（4）Lw/L对网口高度的影响与拖速有一定关系,低速下网口高度变化小,高速下网口高度随Lw/L有明显的变化;（5）Lw/L在大于36.45%之后水动力性能相对较高,增大Lw/L,水动力性能会有小幅度降低,反之会有较大幅度的下降;（6）此规格拖网网袖长度不宜过短,Lw/L以36.45%为宜,根据作业条件,在设计网具时可适当增加网袖长度。试验结果可对大网目底拖网网袖部位的设计和改进提供技术参考。

We evaluated the effects of trawl wing length（Lw） on the performance of trawl gear with large-size mesh. Trawl model tests were carried out in a towing tank at East China Sea Fisheries Research Institute. We measured the effect of Lw/L on the resistance, height of net mouth, and hydrodynamic performance of the trawl by testing six wings of differing lengths attached to trawls of equal longitudinal length（L）. Trawl resistance increased with increasing Lw/L, but was relatively constant when Lw/L exceeded 36.45%. As Lw/L increased, trawl resistance increased at higher speeds. The height of the net mouth increased as Lw/L increased, reaching a maximum when Lw/L was 36.45%–38.69%, then declining. The effect of Lw/L on the height of the trawl mouth was not influenced by trawling velocity. There was little change in the height at lower speeds but a significant change at high speeds. The hydrodynamic performance of the trawl was highest when Lw/L was〉36.45%, and decreased as Lw/L increased further. We conclude that an Lw/L of 36.45% is optimal when designing wing length. However, in practice it may be necessary to lengthen the wing of a trawl based on actual operating conditions.