Hydrodynamics of Polyethylene Knotted Diamond Mesh Netting Panels

Abstract

[Abstract] There is a notable absence of studies about the hydrodynamics of polyethylene knotted diamond mesh netting, widely used in trawl fishing gear. This study presents a detailed experimental study of the drag and lift coefficients of this netting. Experiments were conducted in a towing tank using seven netting samples. We studied the effect of the usual factors that affect the hydrodynamics (solidity, angle of attack and flow speed), but we also considered two additional factors that are not present in square mesh netting but that may have a significant effect in diamond mesh netting: mesh opening and mesh orientation (T0 vs T90). About 1500 experimental data points were generated, covering solidities from 0.09 to 0.77. Our main findings are: (i) available empirical formulae for drag and lift of netting showed significant discrepancies with experimental observations, especially for solidities above 0.3; (ii) the outline drag and lift coefficients are linear with respect the solidity, which contradicts most published empirical formulae; (iii) drag in T0 orientation is less than in T90 orientation, while the lift is greater. Finally, we propose new empirical formulae for drag and lift derived from linear regression with the experimental data, with an excellent goodness of fit.