Axisymmetric trawl cod-ends made from netting of a generalized mesh shape

Abstract

The equations governing the geometry of axisymmetric trawl cod-ends made from netting of meshes of a particular generalized structure are derived. From this, by suitable setting of the initial mesh bar lengths, the equations governing the geometry of cod-ends that are of importance to the fishing industry can be readily deduced. It is assumed that arbitrary membrane forces act normal to the edges of the mesh elements, that there is no shear force acting on the edge of a mesh element and that the twine that makes up the netting is extensible. The case where there is slackness in the mesh bars in the circumferential direction is dealt with and it is demonstrated how the finite structure of a knot can be taken into account. The case where the membrane forces arise solely as a result of and can be expressed by the appropriate components of the tensions in the mesh bars is also examined and numerical solutions are found for a range of examples.