A method for estimating the gear shape of a mid-water trawl

Abstract

An estimation of the shape of the gear (gear shape) during a mid-water trawl and the angle of attack of a cambered otter board can be achieved by implementing a three-dimensional semi-analytical treatment of the towing cable (warp) of a trawl system. This can be achieved by processing the field data obtained using the Scanmar system. The shape of the hand rope, bridles and head (or foot) rope attached behind the otter boards in a horizontal plane was assumed to be a function of the form y r = A x r B . The distance between otter boards (otter board spread) estimated using the three-dimensional analysis of a towing cable system should be equal to that obtained using the functional equation. The shape of a trawl net from wing end to bag net was assumed to be of the form x 2 / a e 2 + y 2 / b e 2 = ( z - c ) 2 / c 2 , i.e., as part of an elliptic cone. The volume covered by the trawl net, the ratio of vertical radius to horizontal radius of the ellipse, the contribution of the side panel to net height and the inclination angle of the head rope (float line) according to towing speed were obtained. The angle of attack of a cambered otter board could be obtained by calculating the equilibrium of forces and moment around the otter board.