On the Behabiour of Bull Trawl Net Estimated by the Tension-records on Net

There are number of unclearfied points regarding behaviour of bull trawl net. The present report therefore aims at presenting basic data on this. Author reports results of some measurement on the tension on bull trawl net and discuss them in this paper. Results obtained can be as follows; (1) In ordinary towing condition, tension on the lacing line of head rope side were 400-700 kg, that on lacing line of ground rope side were 680-1200 kg respectively. (2) In the case of trawling, boats were affected by wind and current from sideway, tension of lee side was 1.5-2.3 times of that of weather side. And then net shape seemed to be unbalanced and this might affect the fishing efficiency. (3) The plane shape of towing rope was made an approximation with an equation of caternary with weight as the net resistance on its top. The result of calculation showed the plane view of towing rope was almost straight line.二そう曳網の漁具にかかる張力を測定してその動態について検討し次のような結果を得た。(1) 筋縄にかかる張力は通常ヘッドロープ側で400~700kg,グランドロープ側で680~1200kgであるが,曳網中に多量の入泥があった場合にはヘッドロープ側で300~700kg,グランドロープ側で1200~1660kgとなる。(2) 側方より風潮流をうけて曳網する場合は風下側の曳索が不足した形となり風下側の張力は風上側の2.2~3.5倍となり網成りも歪んでいるものと考えられる。(3) 曳索の水平形状について中央に網抵抗という重量物を付加した懸垂曲線で近似した結果その形状はほぼ直線となった。これは網抵抗が非常に大きいためと考えられる