Abstract
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.
Highlights
Trawling plays an important role in marine fishing, accounting for approximately 35% of the world’s catches [1,2]
The results show that when the first-order Fourier series was used to fit the motion of codend, the fitted value was the same as the measured value with a very strong correlation (43.3%), but others still have an error compared with the measured value because of a moderate correlation of 10%
H),o1w5.e0v5%er, (t±h0e.4r9e%su),lt1s5r.6e0p%or(t±e0d.4b6y%T),a1n5g.4e7t%al(.±[02.53,52%6]),oannnde1tt5i.n8g2%sh(o±w0.4e0d%th) afotrththeefrcaomdeenddrwagitfhoorucet accounted for a maximum of between 17% and 20% of the total using streamlined frames, close to those obtained in this experiment
Summary
Trawling plays an important role in marine fishing, accounting for approximately 35% of the world’s catches [1,2]. Druault and Germain [13] reported that to optimize the codend efficiency in terms of catchability and its effect on energy consumption, it must have a high static stability, which is difficult due to the significant influence of hydrodynamic turbulence flow They mentioned that the knowledge of flow instability is important to better understand the force acting on a codend and to implement a selected device. Kumazawa et al [20], Zhou et al [21,22], and Yao et al [23] investigated the drag characteristics of the midwater trawl, but different cutting ratios of codend structures exist. In addition to influencing the effect of the cutting ratio on attack angle and contour, it creates a special geometrical shape with the codend that, in turn, influences the hydrodynamic performance of the codend and its catchability, stability, and selectivity. SSixixmmooddeelslsooffccooddeennddssccoonnsstrtruucctetedduussininggnnyylolonnmmaatteerriaiallaannddwwitithhddiifffeerreennttccuutttiinngg rraatitoiosswwereereuusesdedbabsaesdedononthtehme modoedleclocdoednedn(dN(eNt e1t).1T).heTsheecsoedceonddesnwdserwe ecroensctornuscttreudctbeyd abssyeamsbselimngblfionugrfpoiuercepsieocfenseottfinngetwtinitgh awditihama odniadmmoensdh msizeeshofsi3z0emomf 3a0nmdma tawnidneadtiwamin-e edteiramofe3temr mof.3Eamcmh p. iEecaechofpniectteinogf wneatstijnoginwedasbyjopinaerdt 1b(y20pa×r2t51m(2e0sh×) a2n5dmpeasrht )2a(n20d ×p2a5rt m2e(s2h0),×in2a5dmdeitsiho)n, itno caudtdtintigonpatortc2uitntitnogsipxacrut t2tiinngtorastiixoscu(nttoincgutrtaintigo,s6(:n1o, 5c:1u,tt4i:n1g, ,7:62:,1a, n5d:1, 34:1:1)., T7:h2e, acnode3n:1d).pTarhaemceotdeersndanpdajroaimnientgerms eatnhdodjosinairnegshmoewthnoidnsTaarbelesh1oawnndiFnigTuarbele11. and Figure 1
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
