WOW! An Aquaponics Fish Farm that can Propel Itself

Designed to cut energy costs for offshore ocean-based aquaponic farms and aid the movement of such operations into the high seas, the system uses a pair of eight-foot diameter, electrically powered propellers, with 6.2-horsepower underwater motors. The motors are powered through tethers to the surface attached to a diesel generator and a pair of motor controllers mounted on a small boat. Funded by the National Oceanic and Atmospheric Administration's (NOAA) Marine Aquaculture Program, the apparatus produced favorable results during the recent test run at an offshore fish farm in Culebra, Puerto Rico.

Off the shores of Puerto Rico, a test project is underway by researchers with MIT. Scientists with the university's Sea Grant's Offshore Aquaculture Engineering Center are testing a different kind of fish cage: one that can propel itself and not require the use of a massive energy-intensive operation to drag it through the water.

Fish farms have their proponents and their critics. But whether you're of the view that they provide an important source of protein or you think that fish farms breed diseases, there is one fact that's not under dispute: they have to be moved around every so often. That is because conventional fish farms are set up in sheltered waters but have to be moved once disease accumulates. When that happens, the cages are relocated using massive and carbon spewing towboats which haul the cages from one site to its next location.

The spherical fish cage, developed by Ocean Farm Technologies, Inc. of Searsmont, Maine, is fully submerged and able to move itself using slow-moving propellers. The 62-foot diameter mesh sphere bobs along in the ocean with electric powered propellers. Initial tests don't show great results. While the cage maneuvers well, momentum and direction were unpredictable. But the future could show improvement if researchers can successfully outfit these self-propelled fish farms with solar cells or wave motion apparatuses to get them moving without the use of grid electricity.

The movement of cages during deployment, for relocation during fallowing, or for moving fish from the farm site to a harvest site is already a common procedure. Such transits would be simpler and use far less energy employing a high-efficiency, cage-mounted propulsion system. On such occasions the thrusters would be mounted on the cage, with their number and size dependent on the resistance of the cage, the distance to be moved, and the speed requirements due to anticipated tidal currents.

Besides the use of self-propulsion for routine cage movements, the thrusters have additional utility. Often, the limiting factor in cage stocking density is dissolved oxygen levels due to fish metabolism during slack water. The thrusters provide a ready opportunity to supplement water flow through the cage during those brief events, thereby allowing larger crops of fish.

All involved in the testing were impressed with the performance of the thrusters. Steve Page, CEO of Ocean Farm Technologies states, “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 self-propelled harvest pens that may be a great market for this technology.”

This article is courtesy of www.seagrant.mit.edu/news/press_releases.php?ID=54

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