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Ten kinds of trawl gears which are used by six stern trawlers ranging from 100 to 3000 gross tonnage were experimented on hydraulic resistance of gears. The resistance of net itself is estimated theoretically by subtracting the resistance of otter board, warps and hand rope from the total resistance of gears as illustrated in Tables 2 and 3. It can be said that the resistance R (kg) of a trawl net composed of six seams net is approximately expressed as follows. (Fig. 4) R=kabd/lv2 a=The maximum breadth of net body without shrinkage (dotted line seen in the Fig. 3) (meter) b=The maximum length of trawl net without shrinkage (meter) d/l=The average value of ratio: d, diameter of net twine: l, length of each mesh bar at side panel 1-7 section (Fig. 3) k=Resistance coefficient v=Towing speed (m/sec) From the Fig. 4, the value of k, coefficient of resistance, can be read as 8 when there are no catch inside the net, but it takes about twice value as much as the above one when there are some fishes of about 1.5 tons which are gilled in the meshes of the net.
公益社団法人日本水産学会の論文