. Commercial fisheries review. Fisheries; Fish trade. 51. Fig. 3 - Electrical cable wound on winch showing shipboard ter- mination watertight plug. efficiency of transmitting electrical power to the pump is far greater than transporting wa- ter through hoses, a factor that becomes in- creasingly important as the water volume and pressure and length of hose increase. DEVELOPMENT Before the 1920s, hand tonging and hand raking were the common methods used to har- vest surf clams; during the 1920s, dredges were developed that were towed with powered vessels. The dredges were commonly 18 to 28 inch
. Commercial fisheries review. Fisheries; Fish trade. 51. Fig. 3 - Electrical cable wound on winch showing shipboard ter- mination watertight plug. efficiency of transmitting electrical power to the pump is far greater than transporting wa- ter through hoses, a factor that becomes in- creasingly important as the water volume and pressure and length of hose increase. DEVELOPMENT Before the 1920s, hand tonging and hand raking were the common methods used to har- vest surf clams; during the 1920s, dredges were developed that were towed with powered vessels. The dredges were commonly 18 to 28 inches wide with a scraper or knife blade attached between the dredge shoes at a fixed depth. These dredges were prone to clogging with sand and mud, and many clams were broken by the blade. These deficiencies and the need for even more efficient equipment led to the development of the hydraulic jet dredge in the 1940s (Westman, 1946). Hydraulic dredges, a logical step from the dry scraper types, were developed by adding to the dredge a pipe manifold with a few noz- zles or jets directed downward in front of the blade. A fire hose connected the manifold to a pump mounted on the towing craft. Because the water jets loosened the bottom, the dredge could cover a greater area in the same amount of time, and areas were opened to dredging that were too hard for the dry dredges to oper- ate effectively (Westman, 1946). The incidence of broken clams (Parker, 1966) and damaged meats in the catch were reduced substantially by this new development (Ruggiero, 1961). Since its introduction, the hydraulic dredge has increased steadily in size until now 40- inch blades are common, and a dredge with an 84-inch blade is in service on the east coast. The volume of water required has increased correspondingly with the dredge size; a 40- inch or 48-inch dredge requires about 1,600 to 1,800 gallons per minute - -at about 60 pounds per square inch differential pressure between the inside of the manifold
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