A study on sinking and closing performance of falling-net

Based on the real-time data of sinking depth and distance of netmouth of falling-net by SDKN-500 net monitor in November 2014, we analyzed the sinking and closing performance of falling-net. The results showthat: 1) The sinking and closing speeds would not mutate when pursing the purse line with retardation time of 120.7 s; 2) The net mouth was not completely closed when it reached the maximum depth ( averagely 82. 0 m) , and did not rise up until itwas completely closed ( averagely 68.0 s) and stayed for a while ( averagely 9.8 s) ; 3) The different operating conditions could be divided into the shooting time ( 0 s) , the pursing time ( averagely 104.0 s) , the time when the closing speed mutated ( averagely 224.7 s) , the time when the net mouth reached the maximum depth ( averagely 266. 6 s) and the time when the netmouth was completely closed ( average 334. 6 s) in sequence, which were the five key time nodes determining the fishing performance of falling-net; 4) The sinking speeds of the four periods were 0. 419 ms-1, 0.238 ms-1, 0.233 ms-1 and -0.021 ms-1 , respectively, showing a decreasing trend with fluctuation in the middle of settlement; 5) The closing speeds of the four periods were 0.103 ms-1 , 0.105 ms-1, 0.253 ms-1 and 0. 424 ms-1 , respectively, showing an increasing trend. The closing speed of netmouth increased firstly and then decreased at the beginning of settlement, and the closing speed showed a significant increasing trend in the later period of settlement. It is suggested to increase the hauling speed to avoid fish escape.