WORLD AQUACULTURE 33 Deployment The system was successfully deployed in July 2003. All lines and floats were assembled on the sea surface, held in place by slack anchor legs. Using Differential Global Positioning System instrumentation and the design geometry, anchors were systematically pulled into position and set, submerging the grid. To ensure proper static depth of grid lines, indicator lines and floats were secured to subsurface buoys such that floats would be just visible at the surface, indicating that the grid was at the proper depth. Environment Environmental conditions at the offshore site were measured with a monitoring buoy (Irish et al. 2001, 2004). Wave, current and water property data were collected throughout the 12-year history of the project. Calmest conditions occurred during summer, with significant wave heights of 1-2 m and wave periods ranging from 5-7 sec. In winter, typical wave heights increased to 4-6 m and periods of 6-8 sec. The largest waves originated from northeaster storms. One of the largest storm events occurred on 16 April 2007, when significant wave heights were 8.5-9 m and wave period was 12-13 sec (Fig. 4), a 50-year storm for the region. Time series data from the storm indicated surface elevation fluctuation of nearly 30 m (single wave trough to crest height). Currents at the site were measured with an upwardlooking, 300-kHz Acoustic Doppler Current Profiler (RD Instruments) secured to the mooring at the bottom. Tidal currents at the site were nearly uniform with depth, with a maximum velocity of 0.1 m/s. Storm-driven currents were greatest near the surface and decreased with depth, with maximum velocity of 0.5 m/s (1 knot). Additionally, internal solitary waves propagated on the pycnocline (15 m), with water moving northwest at 0.75 m/s above the pycnocline and compensating southeast water movement below. These appeared in groups, separated by tidal periods, with several pulses at about 8-min intervals. Mooring Platform Utilization The submerged grid mooring provided a platform to conduct engineering and biological research projects at an exposed site in the Gulf of Maine. At various times, different cage systems were secured in the mooring, including the SS600 and SS3000 Sea StationsTM by Ocean Spar Technologies, the AquaPodTM by Ocean Farm Technologies, the American Soybean Association’s OCAT system, JPS Industries prototype submersible net pen and standard surface nursery cages (Fredriksson et al. 2005, DeCew et al. 2006, Celikkol et al. 2007, Santamaria et al. 2007, Celikkol et al. 2009). Some of these systems can be seen in Figure 5. While cages were moored to the grid at the site, tensions in mooring lines were measured and compared to numerical model predictions. Biofouling was monitored on cage systems with traditional nylon nets, anti-fouling painted nets and emerging net technologies, such as copper-alloy materials (Langan 2004, Celikkol et al. 2007, Greene et al. 2007). The grid was also used to secure surface structures. Three fish feeding buoys were used to store and deliver feed to fish in submerged cages (Fig. 6). Two feeding buoys (0.25 t and 1 t feed capacity) were attached directly to the grid with traditional and elastic mooring members. The third buoy (20-t feed capacity) had an external mooring but was coupled to the grid with elastic feed hoses. Detailed information regarding buoy (CONTINUED ON PAGE 34) FIGURE 2. A submerged grid mooring capable of securing four fish cages was designed, analyzed and deployed. The grid lines were 18 m below the surface, reducing wear and maintenance requirements. FIGURE 3. Individual components on one corner of the grid. The drawing is not to scale.
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