Imagine a field of windmills, but underwater. Instead of making power only when the wind blows, they would run according to the tide charts, as predictable as the phases of the moon. The East River  not a real river, but a tidal strait connecting Long Island Sound to Upper New York Bay  is famous for currents so strong that sailboats must wait for the tide to turn in their favor.

Those currents ate up the first two generations of turbines, installed by Verdant Power, a small private company, in late 2006 and early 2007. The only way inventors can make anything work is to see how it doesn’t work. And in the saga of the East River turbines, there is already a sharp lesson on the risks of giving up too soon.

For centuries, people have used river power to run mills, to turn water wheels and to make electricity. True rivers run in only one direction. To capture the power of the East (Not Really a) River, all three generations of the Verdant turbines have been designed so that they are automatically swung by the tide and always face the current, whichever direction it is running. They sit on piles drilled into the riverbed, and at low tide are six feet below the surface. Power cables carry electricity onto Roosevelt Island.

The original turbine blades were fiberglass stretched over a steel skeleton.

“They broke on the first deployment,” said Dean Corren, the director of technology for Verdant.

New blades were fabricated from aluminum magnesium, and they held up well, but the flowing water found the next weak point in the machines, along the rotors, or hubs. These snapped within two months. During their limited operation last year, the turbines provided enough power to run a supermarket and light a garage.