Drag forces and deformation of aquaculture cages-Full-scale towing tests in the field

The towing method produced consistent results on deformation in the range from 0.2-1 m/s, and the volume of the net pen decreased almost linearly from 86% (0.2 ms−1) up to 33% (1.0 ms−1). Measured drag forces and their relationship to flow speed were consistent with existing literature. Drag calculations for net cages generally consider flow speed reduction inside the cage due to blockage effects. However, there are large differences in the flow reduction inside net cages found in few laboratory and field studies, which calls for better descriptions of the flow past net cages. This is illustrated by the comparison of drag calculated by a simple, deterministic model, using a static flow speed reduction of 20% inside the cage and a variable flow speed reduction that depends on the ambient flow speed. The results from this study provide valuable information about the interplay of flow speed, net deformation and drag on a full scale fish cage at different flow speeds and underline the need for a better description of the flow past net cages.