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a pass fishnet towed through the water by a special ship, called a trawler; it is designed to catch fish such as cod, haddock, banded sea perch, and other marine life.
A trawl is a conical sack of netting that is held open by rigid elements (a beam trawl) or by the hydrodynamic forces that arise when the trawl is moved (an otter trawl). The second type predominates in modern fishing. In trawling, the fish enter the mouth of the trawl and are drawn into the cod, which is the narrow end part. After the trawl is hauled on board the trawler, the cod is untied and the fish are unloaded into the hold or onto the deck.
There are several types of trawls, such as benthic, bathypelag-ic, midwater (which catch fish in the midwater, or pelagic zone), and general-purpose. The headropes of the largest trawls are up to 150 m long; the vertical opening of such nets is 30–35 m, and the horizontal opening is 50 m. These trawls pass up to 6,000 cu m of water per sec. Light and electric current are used to prevent the fish from leaving the area of the trawl. Fishing is made more efficient by the use of instruments to monitor the trawl. Such instruments make it possible to keep track of the trawl opening, the level of trawling, and the accumulation of fish in the net. The manufacture of trawls from synthetic materials, such as olefin polymers and polyamides, makes possible a reduction of the hydrodynamic resistance of the trawl and an increase in its wear-resistance and service life.
REFERENCEFridman, A. L., M M. Rozenshtein, and V. N. Lukashov. Proektirovanie i ispytanie tralov. Moscow, 1973.
V. V. RANENKO