1.College of Marine Sciences，Shanghai Ocean University，Shanghai 201306，China；2.National Engineering Research Center for Pelagic Fishery，Shanghai 201306，China；3.Key Laboratory of Sustainable Exploitation of Ocean Fisheries Resources，Ministry of Education，Shanghai 201306，China；4.Tokyo University of Marine Science and Technology，Tokyo 108-8477，Japan
Abstract: In order to probe into configuration changes of the trawl configuration gears under different working conditions, the effects of current speed (v), horizontal opening ratio (L/S) and catch on the mouth opening overall shape, drag and energy consumption coefficient were investigated in A 1/35 scale four-pieces krill (Euphausiasuperba) trawl by the Antarctic krill fishing vessel “Longteng” manufactured based on modified Tauti’s law and tested in a flume tank. The tank had the circulating water tank with main dimension of 22.0 m (length)×8.5 m (width)×2.7 m (height), the side observation scale of 9.0 m (length)×2.2 m (width)×1.6 m (standard water depth), and a length of 7.3 m, width 1.5 m viewing window at the tank bottom. The flow rate in the tank was measured by a propeller type flow meter (Tokyo Measurement Technology Co., Ltd.) for 10-200 cm/s with an accuracy of 2%. The results showed that the shape of net mouth tended to be “compressed” with the increase in v and L/S, with the best shape of mouth at L/S=0.35, and v=30 cm/s, without significant effect of the catch on the shape of mouth. The area of the mouth was found to be increased with the increase in L/S at constant v and decreased with the increase in v at constant L/S. There was less change in the area of mouth with simulated catch than that in the empty with the change in current speed, and L/S under the condition of low velocity and high horizontal opening. The net body shape also tended to be “compressed” with the increase in current speed and L/S and the change in L/S had a greater impact on it, the end of net body with simulated catch rose more obviously than that in empty net and the length of net was also increased obviously than it. The trawl net drag force was increased with the increase in L/S, while the energy consumption coefficient was decreased and the change degree of both showed a slowing down trend, both the trawl net drag force and the energy consumption coefficient were increased with the increase in current speed. There were greater drag force and energy consumption coefficient in the trawl net with simulated catch than those in the empty and the larger current speed, and the difference in energy consumption coefficient between net with catch and the empty net was great at high current speed. The finding suggests to keep L/S of 0.35 and the towing speed of 3.0 kn so that the trawl can operate with better fishing performance.
2023, Vol. 38 
