Effects of aspect and camber ratios on hydrodynamic characteristics of biplane-type otter board

To examine the effect of aspect and camber ratios of two cambered boards on the hydrodynamics of biplane-type otter board, a series of experiments was carried out using 1/10 scale models in a circulating water tank. Seven-typ es of cambered boards were used as biplane-type otter board models; four as pect ratios (2.5, 3.0, 3.5, and 4.0) with the same camber ratio 15% and thr ee camber ratios (10%, 15%, and 20%) with the same aspect ratio 3.0. The li ft and drag forces of each of the models were measured at current speeds ra nging from 0.40 to 1.20 m/s. When a pair of cambered boards with the same a spect and camber ratios was assembled in all at the same gap-chord ratio of 0.9 and stagger angle of 30 degrees, there was no effective difference in the maximum life coefficient among models of the four aspect ratios. The ma ximum lift coefficient of the model at camber ratio of 15% was larger than the other two models with 10% and 20% camber ratios. The model with the rea r wing camber ratio larger than the fore one showed higher maximum lift coe fficient. At the gap-chord ratio smaller than 0.9 of the biplane-type otter board currently used by trawlers, the model with the fore and rear wings o f the same aspect ratio of 4.0 showed the highest value in the maximum lift : coefficient.