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

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 degrees. An experiment was carried out using a 1/5 scale model in a circulating water tank. The sinking force, drag and p itching moment were measured with a six-component balance at attack angles ranging from 0 degrees to 80 degrees, and current speeds ranging from 30 to 100 cm/s. Moreover, heel angle was changed from 0 degrees to 30 degrees at 5 degrees intervals, and the effect of heel angle on sinking force was exa mined. 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 t he performances of both types were compared. As for the cambered V-type dep ressor, the maximum sinking force coefficient of 1.57 was obtained at. the attack angle of 20 degrees. It is large, about twice the value of the flat shaped depressor. However, when the attack angle exceeded the boundary whic h obtained the maximum sinking force coefficient, the sinking force coeffic ient decreased rapidly. On the other hand, ii the heel angle is smaller tha n 20 degrees in the case where the depressor rolls, the effects of heel ang le on the performance of the depressor are very small.