MIT Tests Self-Propelled Cage for Fish Farming

A self-propelling underwater cage developed and recently tested by an MIT researcher could not only cut costs for offshore ocean-based fish farms but also aid the movement of such operations into the high seas, avoiding the user conflicts and compromised water quality of coastal zones.

Fish farms account for more than half of the seafood produced globally; 40 percent of the seafood consumed in the United States is farmed in other countries and imported. However, very little of that comes from ocean-based farms.

In conventional offshore fish farming, cages are routinely repositioned to control disease. Stout towboats haul the enormous cages to another site, and both the cage size and typical propulsive inefficiency of boats make such movements very energy-intensive events.

Cliff Goudey, director of MIT Sea Grant's Offshore Aquaculture Engineering Center, is exploring a different approach to moving the cages. By placing large, slow-turning propellers directly on a cage, Goudey frees it from the normal constraints of a boat. His 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.

"These tests demonstrate that the concept of mobile cage operations is technically feasible," Goudey says.

Read the full article published in MIT news on September 2, 2008.