Development of an improved electric trawl-winch control for stern trawlers

Although trawlers are generally equipped with a Ward Leonard electric drive for the trawl winch, hand-controlled mechanical winch brakes are still used during the operation of `shooting the net¿. On modern stern trawlers, the winch brake has to absorb some 200hp, and heavy brake-lining wear has resulted. The paper, after considering the practical problems involved in dynamic braking for this application, describes a new solid-state automatic field control for the winch generator which meets these difficulties by maintaining a constant tension in the trawl warp over a wide range of speeds. A side product of the new scheme is that the speeds of the trawler and winch are automatically co-ordinated at the completion of shooting. Elimination of hand manipulation of the winch brakes paves the way to control the shooting operation from the wheel-house. The paper also describes the laboratory tests carried out with a model simulator to prove the scheme. The results obtained with the model are compared with a theoretical analysis of the system. Finally the paper discusses the problems posed by the need to make satisfactory provision for the acceptance of the regenerative braking power. Different propulsion-machinery arrangements influence the treatment of this problem, and the paper describes the adaption of the warp-tension control scheme to four of the major propulsion and winch-generator drives in current use.