LOWER LINE-SHAPE AND TENSION OF SHRIMP TRAMMEL-NET TOWED ALONG THE HYPOTENUSE OF RIGHT TRIANGLE

Fishing efficiency of shrimp trammel net popularly used in Indonesia c onsiderably depends on the area swept by its lower line. The lower lin e part substituted by a chain was investigated in the present study. A s a simple experiment, the chain was towed by a lorry along the hypote nuse of a right triangle drawn on the floor. The tensions of the towed end of chain were measured by a two-component load cell installed in the lorry. The chain curves were photographed by a camera. From measur ements of the trajectory of chain movement, the moving angle phi was g iven as a linear function of the tension angle theta for the parts of chain far from the hypotenuse, phi=a theta+b, and a constant, phi=alph a (alpha is the towing angle), for the parts of chain near the hypoten use. Substituting these equations for the unknown moving angle functio n in the differential equations, the chain curve and the tension were numerically calculated. When the frictional coefficient was given as m u=mu(90) sin(2) (phi-theta)+mu(0) cos(2) (phi-theta), the calculated r esults well agreed with the experimental results. mu(90) and mu(0) are the frictional coefficients when the chain was perpendicular and para llel to the moving direction.