100尺2枚仕立てトロール網の海上実験

Abstract

For the purpose of obtaining some effective suggestions concerning the construction of the unigan trawl net, the working behaviors of a two piece net (Fig. 1:100 feet in head rope length) were examined on board the Ten'yo-maru (450GT, 1000HP)1), in succession to the previous report2) on the shooting and hauling operation. The results obtained are summarized as follows: 1) The gape height, HNM (m), of the 100-foot net was expressed as a fractional function of the towing speed, V (m/sec), by the following empitical formula (Fig. 2): HNM=2.2/V1.5. 2) The tension, TWP (ton), of warp at the boardside depended both the towing speed, V (m/sec) and the warp length, LWP (m), keeping the following empirical formula (Figs. 3 and 4): TWP=V0.9(1+0.0003 LWP). 3) When the towing speed was very slow, the shape of the warp curved sharply downwards. But, its curvature became less seveer in accordance with increase in the towing speed, and the curve approached very closely to a straight line when the towing speed was higher than about 1.5-1.75m/sec (Fig. 5). 4) The working depth, D (m), of the otter board was indicated, as a continued product of an exponential and a fractional function regard to the warp length, LWP (m), and the towing speed, V (m/sec), by following empirical formula (Fig. 6): D=27e0.0063LWPV-1.5. 5) The working depth of net was about the same with that of the otter board regardless of the towing speed. Hence, the shape of the hand rope (sweep line) during towing was assumed to have a horizontal straight line which is paralell to the sea-bed (Fig. 6).