Hydrodynamic performance of Argentine shortfin squid (Illex argentinus) bottom trawl

Illex argentinus, inhabiting in shallow waters with a short life cycle, is an important economic cephalopod in the high seas fishing ground of the southwest Atlantic Ocean. Squid jigging and bottom trawling are the main fishing patterns to catch this species. However, there are some problems in bottom trawl, such as high energy consumption, and poor matching between vessel and trawl. Thus, it is necessary to understand the hydrodynamic performance of bottom trawl for I. argentinus. In this paper, we conducted a model experiment in the dynamic water tank to explore the effects of towing speed, horizontal spreading ratio, buoyancy weight ratio on the hydrodynamic performance of height of net opening, resistance, coefficient of energy consumption and power consumption. The model net was designed based on the small mesh six-panel single boat bottom trawl used for the main capture of I. argentinus Main scale: 200 m×113.8 m (84.6 m). According to the Tauti's Law, the model experiment was scaled with the large scale ratio of 1∶30 and the small scale ratio of 1∶5. When the towing speed V was 3 kn and the horizontal spreading ratio L/S was 0.54, the buoyancy weight ratio increased from 0.6 to 0.7, the height of the net opening increased from 9.66 m to 14.1 m, and the resistance increased from 73.73 kN to 83.48 kN. However, with the increase of towing speed, the influence of the buoyancy weight ratio on the height of the net opening and resistance decreased. When the sweeping area of trawl opening was less than 200 m², the energy consumption coefficient was greatly affected by the horizontal expansion ratio, on the contrary, it was greatly affected by the height of trawl opening. The power consumption increased with towing speed and horizontal spreading ratio. It accounted for more than 10% of main engine power for vessel when the towing speed was more than 4 kn.