Deformation of Nylon Net and Copper Alloy Net in Fish Cage Models Subjected to Current Velocity

Abstract

Focus in netting material is important in aquaculture industry, which is preventing fish from escape and keeps it safe from predation. In this paper our study mainly focused on the effect of using a variable netting material at cage deformation and tension of mooring system at the same current velocity. The deformation and tension of mooring line was analyzed using two small model fish floating type cages in a flume tank experiment, model A was a Nylon netting material with additional weight sinkers and model B was a copper alloy net cage without additional weight sinkers. However, the two cage models have the same weight in water while any other components and dimensions of the two cage models are the same. In this experiment the deformation of those two models A and B was investigated when exposed to current velocities 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 m/s in a flume tank. The responses of the models by the action of water current were measured using digital camera and load cell at mooring line. Additionally, a digitizer was used to determine the displacement of selected points on netting system. The results from this experiment are presented and discussed to explain the dependency between current force and cage structure. Findings show that at 0.6m/s current velocity i) the volume reduction ratio of copper net is lower than nylon net. Consequently, the drag coefficient is lower when using copper net; ii) tension at mooring system is higher at copper net cage, which corresponds to higher drag force; and iii) the copper net maximize the difference between front wall and rear wall deflection angle which it is directly related with shielding effect. Finally the copper alloy net has a promise in improving biofouling resistance and that leads to reduction in net maintenance for the system.