Computation of drag force acting on fishing nets

Dynamics of a fishing net in a seawater-medium is comparable to that of an aerofoil in an air-medium. However, application of the principles of this dynamics are not fully explored in computing the drag force acting on a fishingnet. A review of existing analytical models indicates that they assume improper drag coefficients in their calculations and hence, predict very low values of drag force. In this paper, a new analytical model is derived based on proper drag coefficients of flow and on the principle that the total drag force acting on a net is composed of drag forces of individual components of the net. The developed model is verified from the results of field experiments conducted with a 50' Burbank Flat Net. This net was instrumented with the underwater, self-recording load cells, and was towed by a twin trawler on a sandy bottom near Shell Island of the Gulf of Mexico. The measured parameters include the speed of the vessel, drag on the net, vertical opening and horizontal spread of the net. The developed analytical model computes closer values of the measured drag forces than the existing analytical equations do.