墳射式 개량조개 桁網의 開發에 關한 硏究

A Study on the Development of Hydraulic Jet Dredges for Catching Surf Clam

In order to develop the fishing method for harvesting the surf clam. Mactra chinensis(PHILIPPI), by hydraulc jet dredge, the authors carried out an excavating experiment using a water-jet nozzle on the sand in a water tank. After that the authors designed and constructed an experimental hydraulic jot dredge on the basis of the results of their water tank experiment, and executed an experimental fishing operation in fishing grounds. 1. Excavating performance of water jet nozzle on the sand in a water tank : 1) Maximum excavating depth and width on the sand by water jet were straightly increased in proportion to the velocity of water jet and the cross section of nozzle, but according to the distance from nozzle tip to water jetted point on sand, the excavating depth was decreased inversely, while the excavating width increased proportionally. 2) A rectangular nozzle wbich the width of hole was Imm was a slightly better than a circular nozzle of same cross section, in the excavating performance. 3) Empirical equations between the velocity of water jet, the distance of nozzle, and the maximum excavating depth and width were expressed as follows at a 45˚, angle of the rectengular nozzle(1X12mm); D = O.0093V0-O.23H+5.7 W = O.OI47V0+I.06H+10.2 where, D is the maximum excavating depth(cm), W is the maximum excavating width(cm), V0 is the velocity of water jet(cm/s) ; 926≤Vo≤1504, H is the distance of nozzle from excavating point on the sand. 2. Performance of the Experimental Hydraulic Jet Dredge : 1) Excavating depth was more than 10-11cm, at a water velocity of 120Ocm/s 11-13cm at the 135Ocm/s, 13-14cm at the 1500cm/s in fine sand and muddysand. 2) Towing tension was only IO5±5kg in 6.7cm/s towing speed. 3) Average catch amount per unit towing area was O.42kg/m and it was 1.2-1.6 times that of the conventional dredge. 4) The Experimental hydraulic jet dredge did not nearly break the surf clam. 5) Turbidity variation by the water jet of dredge were not serious in the fishing ground: On the surface, when the depth was more than 5.2m, turbidity variation was not found at all, and at the 3m layer above the bottom, turbidity variation was increased to the 9-llppm at 1m behind the dredge, but it gradually decreased and was negligable from 9m behind the dredge.