A simplified model of the interaction of the trawl warps, the otterboards and netting drag.

Computational modelling is a valuable complementary tool to assess behavior of bottom trawl fishing gears. A simplified model of the interaction of the trawl warps, the otterboards and netting drag is proposed. The model does not calculate the net geometry and it is constrained to steady towing conditions, flat seabed and gear symmetry. Simulations provide a number of relevant outcomes such us distribution of tensions at the warp, balance of forces at the otterboards or horizontal spread under different haul conditions such as depth or towing speed. Based on the above, the objective of the present study was to describe and implement the model and thus to predict the consequences of changing some gear components, in particular to predict the impact of the doors on the seabed. This objective could have been fulfilled through extensive sea trials to cover all the different haul conditions of interest. Due to the high cost of such trials we chose to perform sea trials at two different bottom depths at which two towing speeds were tested. Then we applied the simulation software to make a preliminary comparison with experimental results and obtain predictions on what would be the effect of changing some gear components.