二重刺網の形状におよぼす波浪の影響 : 波の進行方向と平行に網地を入れた場合について

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概要

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• Meshes of the gill net will be complicated in their shapes by the waves when put in the waters. It seems that the movements of the meshes by the waves, have a great connection with fish-gilling-efficiency of the gear. This paper gives an analysis of observation experiment to the waving states of the meshes, done in applying a model net, one-fifth size in the scale of the actual salmon double drift net, used in the North Pacific Ocean, in being waved artificially in the experiment tank (belonged to Tokai Reg. Res. Lab.). The waving states of the float line and the lead line of the gear, are just same in wavelength, periodic time and velocity, but do not always so correspond to the peaks of waving that the distance of length between the two peaks (Δλ) is observed as shown in Fig. 1. Seeing the relation indicating the values between the wave-length λ and 2Δλ/λ illustrated in the Tab. 2, the peak of the float line in waving is just coincided with the lead line in the lowest waving when the length λ takes a certain value, then it brings about the least favourable function to the net in gilling efficiency. It is considered that though, this value of λ was 4 meters in the case of this experiment net as shown in Fig. 2, the value of λ would be varied according to width of the net. mesh length and shrinking rate of the net. The relation between (2Δλ/λ)×(H/λ) and the value of an average amount of the lengthening and shortning lengthwise of the mesh (Table 3) in calculating on the basis of the Fig. 5, has the interrelation with a linear line as seen in Fig. 8. The results of the experiment come to the conclusion that the value of (2Δλ/λ)× (H/λ) should be smaller in order to keep the favourable condition for gilling, and lengthening and shortening of the meshes less, particularly the value of (2Δλ/λ) should be less than 0.5, and the heavier weight of sinkers, the better, also the length of hanging thread is better to be longer as possible as it could be.

• 公益社団法人 日本水産学会の論文

著者

• 野村 正恒

  東海区水産研究所

• 森 敬四郎

  東海区水産研究所

• 武富 一

  東海区水産研究所

関連論文

• 水中を動く網地が受ける水の抵抗-III : 網糸の種類による流水抵抗の違い
• 水中を動く網地が受ける水の抵抗-IV : 網糸の吹かれ
• 水中を動く網地が受ける水の抵抗-II. 網目の形状の変化と流水抵抗
• 定置網の網地の使用中に起こる抗張力の減退と使用限界張力に関する研究
• 水中を動く網地が受ける水の抵抗 (I) : 本目蛙又及び無結節網地の流水抵抗の違い
• 二重刺網の形状におよぼす波浪の影響 : 波の進行方向と平行に網地を入れた場合について
• 二重刺網の基礎実験
• イワシ刺網の長さの方向における罹網分布に及ぼす縫目の影響
• 底曳網の模型實驗
• 底曳網の網成りと抵抗
• 漁具資材並びに網の構造に関する技術的動向 (昭和45年度日本水産学会秋季大会シンポジウム) -- (定置網漁業に関する研究の現状とその問題点)

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