Experimental method for quantifying resistance to the opening of netting panels

Abstract

Sala, A., O'Neill, F. G., Buglioni, G., Lucchetti, A., Palumbo, V., and Fryer, R. J. 2007. Experimental method for quantifying resistance to the opening of netting panels. – ICES Journal of Marine Science, 64: 1573–1578. In recent years, the tendency in some sectors of the fishing industry has been to use thicker and stiffer twines in the manufacture of netting material. This increases the mesh's resistance to opening and, consequently, reduces the selective performance of fishing gears. The main characteristic of netting twine contributing to mesh resistance to opening is flexural rigidity (EI). We present a methodology for quantifying mesh resistance to opening through the use of a prototype called the resistance to opening and deflection meter (ROD-m). It incorporates four tension load cells and four stepping motors that are driven by four ministep bipolar chopper drives. Small panels of netting (3 × 3 meshes) can be mounted on ROD-m, which can measure the forces acting on the netting and the position of the knots. Estimates of the flexural rigidity of the netting twine can be made from these data. We present the results of the analysis of Mediterranean polyamide netting, and standard and Brezline polyethylene (PE) netting from the North Sea. In all netting, regardless of the material used, EI increases with increasing linear density. Furthermore, Brezline is much stiffer than standard green PE, although they are equally thick.

The influence of twine thickness on the size selectivity of polyamide codends in a Mediterranean bottom trawl

“…The results of the recent PREMECS-II EU project (Sala et al, 2004) suggested that linear density (Rtex) strongly affects the flexural rigidity of the traditional green braid PE netting used in previous studies. However, in codend netting made from braided PA fibres, such as those tested in the current study, the relationship between flexural rigidity and Rtex was less obvious, and there was very little change from one material to the other.…”

Simulation-based study of the combined effect on cod-end size selection of turning meshes by 90° and reducing the number of meshes in the circumference for round fish

“…Sala et al (2004) developed a specific methodology based on the beam theory (Timoshenko and Goodier, 1982) for the measurement of the mesh opening stiffness. They quantified this characteristic through the mesh bar bending stiffness (EI).…”

Inverse Identification of the Bending Stiffness of a Braided Polyethylene Twine Subject to Large Deformation: Application to the Identification of the Mesh Opening Rigidity of Fishing Nets

“…The strong influence of the codend on trawl selectivity has been demonstrated [15]. Moreover, previous studies have shown how mesh rigidity to opening affects the mechanical behaviour, and thus the selectivity of codends ( [5], [16]). However, the mesh opening stiffness is quite difficult to evaluate.…”

“…In fact, it depends on its definition and on the theoretical model of the netting. Generally, to assess the mesh opening stiffness, we consider that a mesh side must have the same behaviour as a beam ( [16], [9], [12], [13]). With this theoretical model, it appears that the bending rigidity EI of the beam represents the mesh opening stiffness.…”

“…As far as the authors know, the first method implemented so far for the assessment of this stiffness was presented by Sala [16]. The method uses a prototype on which netting panels are mounted and deformed.…”