Hydrodynamic characteristics of cambered V-type depressor for sampling midwater trawl

Abstract

To develop an efficient depressor for sampling midwater trawl, a cambered V-type depressor was designed with the camber ratio of 15%, aspect ratio of 6.0 and dihedral angle of 20°. An experiment was carried out using a 1/5 scale model in a circulating water tank. The sinking force, drag and pitching moment were measured with a six-component balance at attack angles ranging from 0° to 80°, and current speeds ranging from 30 to 100 cm/s. Moreover, heel angle was changed from 0° to 30° at 5° intervals, and the effect of heel angle on sinking force was examined. In addition, the model experiment of the flat shaped depressor with the same dihedral angle as a cambered V-type depressor was also done, and the performances of both types were compared. As for the cambered V-type depressor, the maximum sinking force coefficient of 1.57 was obtained at the attack angle of 20°. It is large, about twice the value of the flat shaped depressor. However, when the attack angle exceeded the boundary which obtained the maximum sinking force coefficient, the sinking force coefficient decreased rapidly. On the other hand, if the heel angle is smaller than 20° in the case where the depressor rolls, the effects of heel angle on the performance of the depressor are very small.