底曳網の網成りと抵抗

概要

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The construction of trawl net, of which a model was made for study, is shown in Fig. 1. The modelling was completed according to TAUTIs Principle of model-net construction. Fig. 2 shows the tention of the warps under varions pulling speeds obtained. In the figure, the upper and lower curves differ in the total numbers of floats from one another. Then, from these two curves we obtained the next formulae RA=4.27V1.77+0.07 RB=3.80V1.57+0.135 RA and RB denote the tension of the warps and V the pulling speed. considered as the constant 0.07 or 0.135 may be the friction between net and sea bottom, therefore the hydrodynamic resistance of net is calculated as shown in Fig. 3. The forms of net were photopaphed under the various pulling speeds (Fig. 4). The vertical area of the mouth of net varies with the speed as will be seen in Fig. 5. The hydrodynamic resistance of net (if the form of net does not vary with the pulling speed) can be expressed as (R-C)/a ?? V2. R denotes the hydrodynamic resistance, C the friction between net and sea bottom and a the area of the mouth of net. (Fig. 6).
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