Many methods have been used for the shape approximation of the warp of a trawl. Catenary approximation is one of them. However, as many studies about catenary approximation of a warp have been carried out aboard vessels, it is difficult to standardize experimental conditions. We verified the catenary-application to the warp of a towing net under various conditions using a circulating water tank. We used cord weighted with lead weights and a cone net as the actual warp and a towing net. In the tank, we took photographs of the cord in the flow, changing the length and the weight of the cord and the velocity of the flow. From the photograph we measured the depth of the net. We also calculated the depth by the catenary and compared it against the measured depth. After rectifying for the effect of the billowing of the cord by the flow, the variance between the measured depth and the calculated depth became about 2 %. Therefore it is considered that the current verification of the catenary-application to the warp of a towing net is appropriate.