Influence of main structural parameters on performance of bottom trawl with large-size mesh

To optimize the structure of bottom trawl with lagre-size mesh, we selected a typical domestic single bottom trawl with large mesh as research object. Based on L₉(3⁴) orthogonal table, we designed the orthogonal tests including factors such as the ratio of total length of net to perimeter (L/C), the ratio of headline length to groundline length (S₁/S₂), and the ratio of net body length to total length of nets (L_b/L). Besides, we applied the mean and extreme difference analysis method to detect the influence of above structure parameters on resistance (R), vertical expansion of trawl mouth (H) and energy consumption coefficient (Ce). The results show that with different horizontal expansion, the influence of three factors on R followed an order of L/C>S₁/S₂ >L_b/L, that on H followed an order of S₁/S₂>L_b/L>L/C, and that on Ce followed an order of L/C>S₁/S₂>L_b/L. The L/C of this type of trawl should be relatively smaller than that of trawl with small-size mesh, and the smaller the L/C was, the smaller R would be. Under these conditions, L/C=0.2 was the optimal value when vertical expansion of bottom trawl and energy consumption coefficient were used as indicators. Compared with small-size mesh trawl, S₁/S₂ should be higher, and the higher the S₁/S₂ was, the better the vertical expansion of the net mouth would be. Within the range of 0.83–0.99, S₁/S₂ had no significant impact on the resistance, and S₁/S₂=0.99 was the optimal value when energy consumption coefficient was taken as the indicator. L_b/L decreased with the increase of mesh size, but the decreasing range gradually reduced. L_b/L=0.65 should be suitable for medium or low speed trawl, while L_b/L=0.75 should be more suitable for high speed and fastly towing.