Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

Journal of Marine Science and Engineering

Liuxiong Xu¹  Hao Tang¹  Wei Liu¹  Xinxing You²  Fuxiang Hu²  Shuchuang Dong³ 

[1] College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan;Institute of Industrial Science, The University of Tokyo, 5-1-5 Kashiwanoha, Chiba, Kashiwa 277-8574, Japan;

关键词: cutting ratio;    codend;    hydrodynamic characteristics;    fluttering motions;    the Fourier series;   

DOI  :  10.3390/jmse9030256

来源: DOAJ

【 摘 要 】

The codend of a trawl net is the rearmost and crucial part of the net for selective fish catch and juvenile escape. To ensure efficient and sustainable midwater trawl fisheries, it is essential to better understand the drag characteristics and fluttering motions of a midwater trawl codend. These are generally affected by catch, cutting ratio, mesh size, and twine diameter. In this study, six nylon codend models with different cutting ratios (no cutting, 6:1, 5:1, 4:1, 7:2, and 3:1) were designed and tested in a professional flume tank under two conditions (empty codends and codends with catch) and five current speeds to obtain the drag force, spatial geometry, and movement trend. As the cutting ratio of empty codends decreased, the drag force decreased, and the drag coefficient increased. The unfolding degree of codend netting and the height of empty codends were found to be directly proportional to the current speed and inversely proportional to the cutting ratio. The positional amplitude of codend with cutting ratio 4:1 was the smallest for catch. The drag force of codends with catch increased as the current speed increased, and first decreased and then increased as the cutting ratio decreased. To ensure the best stability and minimum drag force of the codend, it is recommended to use the 4:1 cutting ratio codend.

【 授权许可】

Unknown