Experimental investigation on the hydrodynamic performance of plane nets fouled by hydroids in waves

Biofouling of netting adversely impacts aquaculture operations and the structural safety of fish cages. In this study, the effects of the hydroids on the hydrodynamic performance of a plane net in waves were determined experimentally. A series of plane nets with various levels of biofouling was obtained via field sampling from a fish farm. The hydrodynamic force and motion response of both clean and biofouled nettings in waves were measured in a wave-current tank. The corresponding drag and inertia coefficients of the nettings were then calculated. In the studied waves, the wave force acting on the biofouled netting was as high as 3.88 times that acting on the clean netting. The maximum amplitude of the horizontal motion for the most severely biofouled netting was 3.84 times that for the clean netting. For various wave conditions, the biofouled netting drag coefficients and inertia coefficients were 3.30-7.72 and 5.04-10.83, respectively. The results indicated that netting biofouling by hydroids increases the drag force more substantially than it increases the inertial force.