SOUTH DENNIS, Mass. --

I must down to the sea again, for the call of the running tide/Is a wild call and a clear call that may not be denied.

–John Masefield, British poet

IN APRIL, Verdant Power, of Arlington, Va., installed the last four of six submerged tidal turbines in the East River off Manhattan. These are 35-kilowatt turbines, small compared with Cape Wind’s 3.6-megawatt wind turbines in the proposed Nantucket Sound project, but they are a prototype installation for an anticipated 100-turbine tide farm.

Marine Current Turbine, of Bristol, England, has been operating a 300-kilowatt tidal turbine off the Devon coast for four years, and a Norwegian company, Hammerfest Strom, has been operating a similar turbine in Norway. It is believed that enough tidal energy could be harnessed off the British coast to power 20 percent of Britain’s needs.

The Federal Energy Regulatory Commission has thus far issued preliminary permits for tidal installations at over 25 sites in the United States and is considering an additional 30 applications. Tidal power, like wind power, is on its way.

There are several designs for tidal turbines, but the most common resembles a wind turbine placed underwater to harness energy from the moving tides or, in the case of a river, from the moving current. The blades are much smaller, at about 20 to 50 feet long, because of the limited space between surface and ocean floor and, of course, water-flow considerations.

As with the wind farm, the structures are anchored to the ocean or river bed, and an underground cable would connect the tidal farm to the onshore electrical grid.

One major advantage of tidal turbines is that the tides are predictable and will continue to be so, unless, of course, the moon decides to jump its orbit. Like the wind farm, once the tidal farm is built, power is free. It produces no greenhouse gases or other waste, and it needs no fuel.

In New England, Massachusetts Tidal Energy, of Washington, D.C., has applied for a preliminary permit to build up to 150 tidal turbines between Martha’s Vineyard and the Elizabeth Islands. Each turbine could generate from 500 kilowatts to 2 megawatts and could provide power to 750 homes.

Meanwhile, Energetech, of Australia, is planning to site a 750-kilowatt project for Point Judith, and Meredith Management is looking into the feasibility of siting an installation in the Palmer River.

One misconception is that tidal turbines will be entirely submerged and out of sight. The turbine’s supporting structure will extend above water so that the turbine can be hoisted above the surface and accessed by boat for maintenance. (See illustration below.) Just as there is no free lunch, there is no invisible energy source for those who believe they own the view.

Tidal-power projects are basically in their infancy, whereas wind power now has a 25-year history and wind-turbine technology is now in its third or fourth generation. But there is one inescapable fact: Our demand for energy continues to increase at a rapid rate, with some estimates putting the increase as high as 50 percent in the next two decades.

We have plenty of coastline, therefore plenty of wind and plenty of tide. And we have other emerging energy-producing technologies, such as wave power and geo-thermally derived power. There is no reason that, with our technological expertise, we cannot, sooner rather than later, wave adieu to our dependence on foreign oil and, to a large extent, fossil fuels in general.

Our biggest stumbling block, paradoxically, is neither lack of scientific ability nor any natural obstacle. It is our increasingly transparent and arrogant politicians of both parties who repeatedly throw up egregious special-interest roadblocks to innovative energy projects and who no longer even care if the voters know they are bought and paid for by the rich and infamous.

All it takes is the will to rid ourselves of these odious shills to move forward with clean, renewable energy. Technologically, we already have the way.

Solon Economou, a frequent contributor, is an engineer and Cape Cod-based writer ( capecodder1@hotmail.com).