Scale model of a new midwater trawl system for sampling pelagic larval andjuvenile fish

A new midwater sampling trawl was designed to collect pelagic larval and ju venile fish. It has a rigid square frame of 2.25 m(2), with a 12.5 m high s trength polyethylene net. The cambered V-type depressor with a camber ratio of 15%, aspect ratio of 6.0, and dihedral angle of 20 degrees was hung to the bottom of the frame with four slings based on the principle of the para llelogram. A 1/5 scale model net of the prototype was made to examine the t owing performances in a circulating water tank. The depth of the net and th e attack angle of the depressor were measured at various flow velocities ra nging from 30 to 100 cm/s with warp lengths of 260, 310, 360, 410 cm. The d epressor held the setting angle closely, and the fluctuating range of the n et depth was only 2% for the longest warp length over a wide range of flow velocities. This sampling trawl could maintain near constant depth under va rious flow velocities by the results of model experiment.