Model experiments of improved SURF-BRD trawl

The SURF-BRD is comprised of two panels (front panel with large mesh and re ar panel with small mesh) and two side escape-vents for fish escapement. On ly fish that pass through the front panel can escape from the side escape-v ent and hence the BRD has size selectivity of the front-panel mesh size for fish encountering it. To ensure size selectivity in the improved BRD trawl , the selvedge ropes to which the ends of the front-panel headline were att ached was installed at the center of the belly, which is 1.5 times higher t han the prototype BRD trawl. This study examined four factors (buoyancy of floats on the BRD headline, the angle of rear panel, the volume of catch, a nd towing speed) affecting the height of the BRD and the trawl using a 1/10 -scale model in a circulating water tank. The BRD height was strongly affec ted by the towing speed and the buoyancy of the floats with its relationshi p: to the configuration of the whole trawl net. At the towing speed of two knots with catch in the cod-end up to 40 kgw, the BRD trawl with the BRD he adline floats of 6.5 kgw buoyancy and the rear panel installed at the angle of 45 degrees can keep the BRD height about 1.0 meter.