Studies on the Otter Board, Performance of the Multi-plane Otter Board

Studies on midwater otter boards which are mainly composed of Wing board (Larsson’s Phantom trawl), Dualfin board (British Columbian trawl), Hydrofoil otter board (Süberkrüb) and Bie-plane otter board (Kobayashi), are comparatively recent development. This paper deals with the performance of multi-plane otter board, whose structure is similar to that of a paravane-shearing-board. The model experiments were carried out on sea and at circular tank. The model was made with galvanized iron-plate (0.48 mm in thickness), dimension of the model being 23.4 cm in length, 21.7 cm in width, and 225 g in weight, respectively. The results obtained are as follows; 1．The critical attack angle of the multi-plane otter board was determined to be 25.5 degrees. 2．Through the results of fig. 6 the relationship between lift-force and towing-speed, and, between drag-force and towing speed may be expressed in the following empirical formulas. L=42.7V^{1.99}. D=34.4V^{2.05}. 3. The ratio of lift and drag in the multi-plane otter board was ascertained to be 1.28, which shows the intermediate value between the upright type otter board (C_L/C_D=1.85), and the ordinary one (C_L/C_D=0.8)