This study deals with the shape of groundrope in bottom trawl nets. The shape of groundrope depends on the equilibrium of three forces acting on it: the fluid-dynamic resistance of the netting, the fluid-dynamic resistance of the groundrope, and the sliding frictional force against the sea bed. The shape of groundrope in towing condition was studied on the basis of field experiments in the East China Sea and on theoretical laboratory analysis. Experi-mental results were analyzed with respect to the attack angle of bobbins. The authors analyzed the shape of groundrope based on the assumption that the catenary, the density of twine, in-creases towards the center. The groundrope was divided into small segments and the forces acting on them were calculated. The fluid-dynamic resistance of the netting and the sliding frictional force against the sea bed were calculated in proportion to the amount of the netting area and the weight of the groundrope, respectively.
Two shapes of groundrope, symmetrical and asymmetrical, were obtained by field ex-periments and were compared with theoretical values obtained from laboratory experiments. Both the symmetrical and the asymmetrical shape agreed with the theoretical values, calculated on the basis of the combined top shape of groundrope for convenience. It was proven that the method of analysis employed in this study was effective in considering the shape of ground-rope.
