日向灘イワシ巾着網模型実験-5-
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概要
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In the previous paper, it was pointed out that there exists fluttered webbing around a purse line in the early stage of pursing. This may indicate that the gear is not completely free from the chance of entanglement, if this phenomenon is caused by unstable webbing around the purse line. In order to avoid this trouble, it seems desirable to decrease the amount of unstable webbing around the purse line by hastening the sinking of bottom margin of the net or by cutting off the needless portions of webbing. In the present experiment, the comparision between a cotton purse seine and a Saran (polyvinyliden chloride) purse seine in the sinking behaviours of the bottom margin of the net was made. The result was summerized in Fig. 2. It was found that the sinking movement of the bottom margin of the net was in a uniform motion in both the cases, and that the speed of sinking was about 8m./min. in the cotton seine while about 11m./min. in the Saran seine.