Experimental study of installation procedure and volume estimation of tarpaulin for chemical treatment of fish in floating cages

In the salmon industry chemical delousing is done by enclosing the cage in a tarpaulin, and then mixing the chemical agent in the enclosed water volume. Correct dosage is important to obtain the wanted effect, and in order to calculate the correct dose of the agent the volume of the enclosed water is estimated based on the geometry of the tarpaulin. The accuracy of this volume estimation is investigated by model experiments in a flume tank. Different tarpaulin shapes, installation procedures and current velocities were examined, and in addition to measuring the volume of the enclosed water, the drag force on the cage/tarpaulin was also measured. The accuracy of the volume estimation was found to be quite low (Root-mean-square (RMS) value of the deviation between estimated and measured volume for all runs was 21%). Certain combination of tarpaulin shape and installation procedure showed less deviation between estimated and volume, and it was found that increased current velocity was favourable with respect to this accuracy.