Hydrodynamic performance of bottom trawls with different materials, mesh sizes, and twine thicknesses

Abstract Nowadays, the fishing industry faces several constraints such as continuous increase infuel price and decrease in fish stocks. Bottom trawl efficiency is mainly affected by the drag force of trawl net and sweep area during fishing operations. This study focuses on the drag of bottom trawl models constructed from traditional and new materials. A nylon net panel, a traditional material, was used in two model trawl nets, namely, trawl nets 1 and 4; the geometric shape ofwing net on trawl net 4 was a triangle. Considering the physical characteristics of the new materials such as Dyneema and nylon monofilament, net panels with a large mesh size and small twine stiffness were used, respectively. The trawl nets were named as trawl nets 2 and 3, respectively. The drag forces provided by the standard trawl (trawl net 1) were 57%, 56.2%, and 47% less than those of trawl nets 2,3, and 4 respectively. The drag coefficient of trawl net 1 was 40.68%, 30.35%, and 33.96% greater than those of trawl nets 2, 3, and 4, respectively. The results also show that these three trawl net models are geometrically efficient in terms of net mouth height than a standard trawl net. This indicates that the drag force of bottom trawl net with a new material was much lower than those made with a traditional material. The developed equations in this study provide the basis for a drag and geometry prediction model for a bottom trawl. The advantage of this predicted drag equations over previous net drag formulas is that it can be evaluated using only information available from a net drawing (mesh size and twine diameter), so that the net drag of bottom trawl net of a reasonably standard shape can be estimated at the design stage.