Numerical Analysis of a Mid-Water Trawl System With a 6-DOF Otter Board Model and Sea-Trial Verification

In this paper, we proposed a mathematical model of a mid-water trawl system. The model consisted of towing warps, otter boards, a trawl net, and other rigging components. The warp and the net were modeled with the lumped mass method. The otter board was modeled in 6 degrees of freedom, and the variation in the otter board's hydrodynamic parameters with different yaws, pitches, and roll angles was also considered. We used a first-order approximation to simplify the relationship between the otter board's hydrodynamic parameters and its working angle, and the coefficients included in the otter board model were then estimated using the sea trail data. With this approach, the movement of the otter board was simulated, and its influence on the trawl gear performance was analyzed. The final results of the door depth and the door spread with warp lengths from 200 to 900 m showed good agreements with the sea trail data, and the mean normalized absolute error between the simulation and the measurement was approximately 5%.