- Volume 35 Issue 2
The shape of the net mouth in a midwater trawl gear is examined by measuring towing speed, gear resistance, the width of otter boards, net height, and so on of a full-scale gear in operation. In addition, a mathematical model is developed to predict shapes of the net mouth. In the model, shapes of head, ground, side ropes, which governs the shape of net mouth, are assumed as a catenary. The validity of the model is tested with observations. The results can be summarized as follows: 1. The warp tension and vertical opening of the gear is highly dependent to the towing speed. The depth of the gear and width of otter boards are very sensitive to the variations of the warp length. 2. The model results indicate that the wing tip of the head and side ropes is reduced and the vertical distances of the head and side ropes sagged to the back with increasing towing speed. 3. The results of comparing the measured net height with calculated side rope height were satisfying. 4. The results of analysis showed the vertical axis of the net mouth was decreased and the width of the net mouth was little changed when the towing speed increased.