Hydrodynamic Performance Of An Argentine Shortfin Squid (Illex Argentinus) Bottom Trawl

Argentine shortfin squid(Illex argentinus)is an economically important cephalopod with a short life cycle,which is also an important target species mainly harvested by squid jigging operating in the high seas of southwest Atlantic Ocean.In recent years,there are 34 Chinese bottom trawlers fishing in the high seas of the Argentine continental shelf.In 2020 and 2021,the total catches for this fishery rapidly reached 75,000 tons and 147,000 tons,respectively,among which catches for Argentine shortfin squid accounted for nearly 80%,with remaining species including ray,hake and Antarctic ice fish.On basis of fishing logbook statistical data,months with high CPUE are concentrated in March to May with the corresponding monthly averaged catches over500 tons.From the perspective of healthy stock status,bottom trawling fishery in this region has a wide range of developing prospect.In this paper,a series of hydrodynamic performance investigations were carried out on the small mesh six-panel single boat bottom trawl(main dimension 200 m×113.8 m(84.6 m))equipped by the 2700 HP Argentine shortfin squid bottom trawl vessel owned by Lianhai Fishery Co.,LTD,Shandong province.Based on the model experiments and numerical simulation approaches,we analyzed the effects of towing speed,horizontal spreading ratio(L/S),buoyancy-weight ratio on the hydrodynamic performances including the height of net opening,resistance,coefficient of energy consumption and power consumption.The horizontal spreading ratio of trawl is 0.46,0.50 and 0.54,and the buoyancy-weight ratio of trawl is 0.6 and 0.7.(1)The height of net opening increases with the buoyancy-weight ratio,while decreases with the increase of the towing speed and L/S.In the low-speed region with towing speed less than 4.0 kn,increasing the buoyancy-weight ratio or reducing the horizontal spreading ratio of the trawl has a significant impact on improving the height of net opening,while a more evident effect of the height of net opening could be achieved by increasing the buoyancy-weight ratio of the trawl.However,under condition of the towing speed more than 4.0 kn,adjusting the buoyancy-weight ratio or the horizontal spreading ratio of the trawl has insignificant effect on the height of net opening.When the towing speed is 3.0 kn,3.5 kn and 4.0 kn,respectively,the maximum height of net opening is approximately 11.0～15.5 m,7.0～11.0 m and 6.0～7.0 m,respectively.When the towing speed is 4.5 kn,the maximum height of net opening is only approximately 5.0m;In the case of towing speed increasing to 5.0 kn,the height of net opening will drop below 4.0 m.(2)The resistance increases with towing speed,L/S and buoyancy-weight ratio.Under condition of a constant L/S,the resistance increases significantly with buoyancy-weight ratio,but under condition of the towing speed more than 4.0 kn,the effect is significantly weakened.In the case of towing speed 3 kn,horizontal spreading ratio 0.54,when buoyancy-weight ratio increases from 0.6 to 0.7,the resistance increases from 73.73 k N to 83.48 k N.In the case of towing speed 3.5 kn,horizontal spreading ratio 0.54,when buoyancy-weight ratio increases from 0.6 to 0.7,the resistance is more than 90.0 k N.However,under condition of the towing speed more than 4.0 k N,the resistance is 95.0 k N to 110.0 k N.(3)The coefficient of energy consumption is mainly affected by the resistance and sweeping area.The coefficient of energy consumption increases with the towing speed and decreases with the increase of the buoyancy-weight ratio,but the effect of buoyancy-weight ratio on the coefficient of energy consumption is weakened when towing speed is more than 4 kn.In the case of towing speed 4 kn,when L/S is 0.46,0.50and 0.54,respectively,the difference values of the coefficient of energy consumption under the two groups of buoyancy-weight ratio is 0.122,0.181 and 0.249,respectively.The coefficient of energy consumption is affected greatly by horizontal spreading ratio with sweeping area less than 200 m~2,while by the height of net opening with more than200 m~2.(4)The power consumption depends on the resistance of bottom trawl.Power consumption increases with towing speed and horizontal expansion ratio.But under the condition of the towing speed more than 4.0 kn,the effect of buoyancy-weight ratio on power consumption is negligible.In the case of buoyancy-weight ratio 0.7,the towing speed 5 kn,when horizontal spreading ratio is 0.46,0.50 and 0.54,respectively,the power consumption is 308.1 k W,327.7 k W and 356.1 k W,respectively.The results showed that the experiment net was heavy and it was difficult to ensure high towing speed in production,which verified the experience of fishermen in actual production.