Trawling is one of the methods of fishing. In this paper, single boat trawling is taken up and the method to calculate the motion of a trawl net system using the lumped mass method is shown. In calculation, rational simplification of the trawl net system (creation of an approximation model) is made. The calculated results were in good agreement with model experimental results.
Trawling is one method of fishing in which a large fishing net is pulled through the water by one or two boats. A system of wires between the boats and the net and an adequate towing speed are required to hold the mouth of the net open during operation. When two boats are used, one warp line attached to each boat spreads the net horizontally. However, single boat trawling (Fig.1) is also used frequently. In this case, the horizonal spread of the net is provided by trawl boards installed between the boat and the net. The trawl boards essentially act as wings. A vertical opening of the net is created using floats on the upper edge ("head line") and weight on the lower edge ("ground line") of the net mouth.
In order to catch fish efficiently the net mouth must be kept at an appropriate depth and must be open to the maximum irrespective of navigation of the boat. To handle these features without depending on the experience of a chief fisherman or a captain, an accurate simulation of the motion of the net, wires and trawl boards is required, and a lot of research has been done (Miura et al. 1991, Hu et al. 1995, Priour et al. 1999, Lee et al. 2000, Wan et al. 2002, Suzuki et al. 2003).