A numerical model has been developed to calculate the resistance of the different components of a trawling gear, by deduction of the drag and lift components. For this purpose, mathematical models have been considered for all the elements, such as trawl cables, floats, doors, and the net itself. The most important contribution of this numerical model is that the action of forces upon different elements permits modifying the geometric configuration of the complete set with a mutual accommodation of resistance and geometry, simulating the actual dynamics, where forces and geometry converge toward an equilibrium state. Some results obtained from actual fishing gear with data obtained from sensors during sea trials are used to compare the results of the simulator.