Free seine nets are an active form of fishing. The ship sails on the sea looking for a school of fish. When detecting a school of fish, use a seine net to catch it, so it can be caught both during the day and at night (fish is detected at night thanks to the phosphorescence emitted by the fish when moving). Due to the need to catch fish that are moving at a fast speed, this type of seine net requires a long net length and a high height. In Vietnam today, fishermen often use gold net length L = 900-1500m, net height H = 100-160m, mesh size 2a = 20-80mm. For fish with a higher swimming speed, the greater the length and height of the seine is required.