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Self Propelled Aquaculture Cage
Culebra, Puerto Rico, was the site of a unique project exhibiting the potential of the Self-Propelled Aquaculture Cage. As part of a project led by Cliff Goudey, director of MIT Sea Grant's Offshore Aquaculture Engineering Center (OAEC). Goudey conducted the tests at Snapperfarm, Inc. The spherical cage, developed by Ocean Farm Technologies, Inc. of Searsmont, Maine, was an Aquapod with a capacity of 3,250 cu. m. The project is funded by NOAA's Marine Aquaculture Program, aimed at demonstrating the technology needed to raise fish in the vast portions of the U.S. EEZ that are too deep for conventional anchored fish cages. By operating while submerged and in predictable ocean currents, mobile fish farms need only a modest means of positioning to stay within planned trajectories. There are many locations both in U.S. waters and around the world where oceanic currents and gyres offer useful frameworks for such mobile operations. Goudey`s approach was to exploit the inherent efficiency of large-diameter, slow-turning propellers. Placing propellers on a cage frees it from the normal constraints of a boat. The system uses a pair of eightfoot diameter, electrically powered propellers, with 6.2hp underwater motors. Through a two-stage reduction gear, the propellers turn 42 rpm at full speed. By fixing a pair of the units to the mid-depth of the 62-ft. diameter Aquapod, in a horizontal line nine feet apart, he was able to maneuver the cage like any twin-screw vessel. The thrusters were installed on the Aquapod and a suit26 MTR
able amount of fixed buoyancy was added to balance their combined underwater weight of 800 pounds. The three-phase motors were powered through tethers to the surface and a diesel generator and a pair of variable-frequency motor controllers mounted on Snapperfarm's small harvest boat. After the intial tests, Steve Page, CEO of Ocean Farm Technologies said, "My opinion of the thrusters is very high. I want to consider using them to help with future installations. There is also a growing demand for selfpropelled harvest pens that may be a great market for this technology." Brian O'Hanlon, founder of Snapperfarm, said, "I was incredibly impressed with the power and efficiency of the thrusters and Cliff 's ability to steer the cage. I see this technology having a broad range of applications in mariculture and other marine industries. This futuristic concept of farming the high seas just came one step closer to reality." With the technical feasibility proven, Goudey will be turning his attention to assessing the system's economic viability, both as a tool for routine cage movements in offshore fish farming and in a business strategy involving mobile cages associated with specific routes in concert with predictable ocean currents or tidal gyres. This future work will involve the collaboration of ocean modelers and aquaculture business people. (Source: Excerpted from http://seagrant.mit.edu)
June 2009
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