Hydrodynamic characteristics of the oval cambered double slotted otter board in bottom trawl fisheries

Abstract

The otter board is one of the main components of single boat trawl fisheries. An oval cambered double slotted otter board was developed for improving the expansion performance of trawl net in bottom trawl fisheries. A flume model experiment was conducted to measure the lift coefficient (CL), drag coefficient (CD), and lift to drag ratio (K) in different angles of attack (α). The experimental results are as follows : (1) The CL and K value show a trend of increasing at the beginning and then decreasing with the increase of angle of attack, the CD value reflects an upward trend as the angle of attack increases; (2) The D3 otter board (front flow deflector angle at 29°) showed a better hydrodynamic performance. When α=30°, the max lift coefficient (CLmax) was 1.464, in this case CD = 0.554 and K=2.643. When α=15°, the max lift to drag ratio (Kmax) was 4.165, CL =0.633, and CD = 0.152. This suggests that the best working scope for the angle of attack is between 15°~30°, in which case, CL>0.633 and K>2.643. The mean value of the lift coefficient was 1.071 and the mean of the lift to drag ratio was 3.482. Comparative analysis of the hydrodynamic performance of different types of otter boards showed that the D3 otter board both had good expansion performance and efficiency, which can provide a reference basis for further optimization of the bottom trawl otter board.