船尾トロールの投揚網時におけるワープ張力の測定結果
1968 年 34 巻 10 号 p. 903-908
詳細
1968 年 34 巻 10 号 p. 903-908
There are few measurements on tension imposed on warp while shooting or hauling trawl. The present paper describes the results which were measured by a tension meter set on the Kaiyo-maru, the biggest experimental research vessel in Japan, operated at rough sea and calm one. The structure of the otter boards and trawl net used for the experiment is shown in Figs. 1 and 2.
1. Warp tension while shooting trawl.
Tension of 4-5tons each warp was recorded while shooting (vessel speed 6knots; shooting speed 100m/min.) at rough sea. That increased to 10-12tons when shooting was braked every 100-200m for the extension of trawl net. The values of tension were nearly equal to those measured at calm sea.
2. Warp tension while pulling and hauling.
At calm sea tension of 5-6tons each warp was recorded while pulling (warp length 500m; pulling depth 124m; towing speed 4knots), and that decreased to 3-4tons when pulling was changed into hauling (hauling speed 90m/min.; towing speed 0.5-1.0knots). Tension while hauling was not changed particularly when the otter boards and net left the sea bottom.
It was measured at rough sea that each tension of warps fluctuated from 4tons to 8tons in pulling (warp length 600m; pulling depth 150m; towing speed 4.2knots). When the otter boards and net left the bottom by hauling, the fluctuation of warp tension became violent suddenly, and 23tons on one of the paired warps and 38tons on both ones were recorded at the maximum.
