Balash Cheslav, Sterling David, Binns Jonathan, Thomas Giles, Bose Neil
National Centre for Maritime Engineering & Hydrodynamics-Australian Maritime College, University of Tasmania, Launceston, Tasmania, Australia.
Sterling Trawl Gear Services, Brisbane, Queensland, Australia.
PLoS One. 2015 Mar 9;10(3):e0119622. doi: 10.1371/journal.pone.0119622. eCollection 2015.
For prawn trawling systems, drag reduction is a high priority as the trawling process is energy intensive. Large benefits have occurred through the use of multiple-net rigs and thin twine in the netting. An additional positive effect of these successful twine-area reduction strategies is the reduced amount of otter board area required to spread the trawl systems, which leads to further drag reduction. The present work investigated the potential of redirecting the drag-strain within a prawn trawl away from the wings and the otter boards to the centre line of the trawl, where top and bottom tongues have been installed, with an aim to minimise the loading/size of the otter boards required to spread the trawl. In the system containing the new 'W' trawl, the drag redirected to the centre-line tongues is transferred forward through a connected sled and towing wires to the trawler. To establish the extent of drag redirection to the centre-line tongues and the relative drag benefits of the new trawl system, conventional and 'W' trawls of 3.65 m headline length were tested firstly over a range of spread ratios in the flume tank, and subsequently at optimum spread ratio in the field. The developed 'W' trawl effectively directed 64% of netting-drag off the wings and onto the centre tongues, which resulted in drag savings in the field of ∼20% for the associated 'W' trawl/otter-board/sled system compared to the traditional trawl/otter-board arrangement in a single trawl or twin rig configuration. Furthermore, based on previously published data, the new trawl when used in a twin rig system is expected to provide approximately 12% drag reduction compared to quad rig. The twin 'W' trawl system also has benefits over quad rig in that a reduced number of cod-end/By-catch Reduction Device units need to be installed and attended each tow.
对于对虾拖网系统而言，由于拖网作业能耗大，减阻是重中之重。通过使用多网 rigs 以及网具中使用细网线，已取得了巨大成效。这些成功的网线面积减小策略的另一个积极效果是，展开拖网系统所需的拖板面积减少，从而进一步降低了阻力。本研究探讨了将对虾拖网内的拖曳应变从网翼和拖板重新导向拖网中心线的潜力，拖网中心线处已安装了上舌板和下舌板，目的是尽量减少展开拖网所需的拖板负载/尺寸。在包含新型“W”形拖网的系统中，重新导向至中心线舌板的阻力通过相连的雪橇和拖缆向前传递至拖网渔船。为确定导向中心线舌板的阻力大小以及新型拖网系统的相对减阻效益，首先在水槽中对网口长度为3.65米的传统拖网和“W”形拖网在一系列展开比下进行了测试，随后在实地以最佳展开比进行了测试。所研发的“W”形拖网有效地将64%的网具阻力从网翼转移至中心线舌板，与单拖网或双 rig 配置中的传统拖网/拖板布置相比，相关“W”形拖网/拖板/雪橇系统在实地的阻力节省了约20%。此外，根据先前公布的数据，新型拖网在双 rig 系统中使用时，预计与四 rig 相比可减少约12%的阻力。双“W”形拖网系统相对于四 rig 还有其他优势，即每次拖曳时需要安装和照看的囊网/副渔获物减少装置单元数量更少。
