Tow Test Results of an AquaPod Fish Cage

The AquaPod^TM system, developed by Ocean Farm Technologies Inc., is a submersible, spherical net pen. This cage was deployed at the University of New Hampshire´s (UNH) Open Ocean Aquaculture (OOA) site for seven months for testing purposes. The cage was towed from Portsmouth Harbor to the UNH OOA site, located 15 km offshore in the Gulf of Maine, in September 2005. Water velocity and tow line tension measurements were recorded with the cage fully submerged. These values were used to determine the flow blockage caused by the cage framework and net at various speeds. Results of this tow test are being used to enhance the numerical modeling capabilities of aquaculture cage systems. The test set-up consisted of Marsh-McBirney EM and Nortek Aquadopp current meters and a Sensing Systems 53 kN load cell. The Marsh-McBirney was secured to the side of the tow vessel to measure the relative water velocity of the cage. The load cell, used to measure the towline tension, was also placed on the tow vessel. These instruments were used to record and view the water velocity and drag loads in real-time for towing purposes. The cage´s interior water velocity was recorded by an Aquadopp current meter placed in the center of the cage to determine the current reduction. The cage system was brought to 5 velocity levels (constant vessel engine RPM) over 15 minutes. Each velocity level was held for approximately 2-3 minutes. The load cell measured loads from approximately 6.1 kN (1370 Ibf) at 1.08 knots to 32.2 kN (7250 Ibf) at 2.04 knots. A significant current reduction within the cage was also measured.