Henryk SENDŁAK
Academy of Agriculture, K. Królewicza 4, 71-550 Szczecin, Poland

Key words: fishery, trawling system, pelagic trawl, fiber materials, trawl drag, opening parameters.

Abstract.
In order to decrease the drag of the trawling system, new generation Dyneema SK 60 fibers, whose strength is three times greater than the strength of polyamide fibers used so far, were applied in the trawl mouth. Tests were performed on scale models of the giant trawl design of a mouth circumference of 2,520 m for catching scattered shoals of fish in the open ocean with the use of 3,600 kW trawlers. A 1:10 scale model was constructed and tested in a lake used for conducting experiments by the Department of Fishing Technology of the Academy of Agriculture in Szczecin. The rigging of the models was identical. The values of vertical and horizontal opening and trawl door spread obtained when towing the models made entirely of polyamide and the models with Dyneema fibers in the mouth turned out to be similar, and the differences did not exceed a few percent. By contrast, the drag of the design made partially of Dyneema was clearly lower within the whole range of trawling speeds. From the comparison of drag forces when towing both the trawl designs, it emerges that the drag of the model made in part of Dyneema is 10-16% lower than the drag of the model made entirely of polyamide.