Effects of bottom trawl body with lagre-size meshes on net performance

Trawl net body has important influence on trawl net hydrodynamic performance. When the perimeters of net mouth and net structure of wing sections are fixed,the body structure of trawl net is very important in remaining net stability,leading fish into the codend,and improving trawl net performance when trawling in the water. One large mesh bottom trawl: 1296. 00 m × 181. 00 m( 159. 60 m) widely used in the East China sea,was selected for study in this paper. Trawl model test in flume tank was conducted to research effects of the ratio of net body length to net mouth perimeter( Lb/ C) on the trawl resistance,the height of trawl mouth as well as the coefficient of energy consumption,and to propose the optimum regions of net body design parameters. The experimental results were as follows:( 1) when the perimeters of net mouth and net structure of wing sections were fixed,the resistance had positive correlation with Lb/ C,and had little change in the towing speed of 2. 5- 3. 0 kn;( 2) when Lb/ C was between 0. 10- 0. 13,the resistance of trawl was the lowest and almost invariant,while Lb/ C increased to 0. 13 and more,resistance increased obviously;( 3) Lb/ C had evident effects on the vertical expansion of net mouth,when Lb/ C = 0. 13 the vertical open of net mouth reached the maximum;( 4) when Lb/ C was 0. 10- 0. 13,the coefficient of energy consumption was the minimum under the present laboratory conditions;( 5) the body length of trawl influenced the performance of trawl more in high speed than in low speed,and trawl meshes were easier to open in high speed. The experimental results had some guidance for the design of large-mesh-size bottom trawl used in the East China Sea.