With construction underway, two Louisiana firms with roots in the oil and gas industry are playing a leading part in what could be the nation’s first offshore wind farm.

Once it’s operating next year, Deepwater Wind’s Block Island project is in line to generate 30 megawatts of electricity — enough power for 17,200 homes — roughly 3 miles off Rhode Island’s coast.

The massive steel foundations for the wind farm’s five turbines were designed by Keystone Engineering, of Mandeville, and built by Gulf Island Fabrication in Houma.

The two Louisiana firms were a natural fit for the project: Though destined for the East Coast, the foundations were modeled on offshore technology used by the oil industry in the Gulf of Mexico.

“It was a nice bit for two Louisiana companies who have been in the oil and gas industry for more than 30 years to put their experience together and try to come up with a solution,” said Kirk Meche, president and CEO of Gulf Island, which has about 700 workers in Louisiana.

Deepwater Wind’s turbines are supported by a traditional “jacket” foundation, which resembles a radio tower. Keystone’s innovative design puts the structure’s three legs twisted around a central column, which makes it easier and less expensive to build. Using more than a dozen construction and transport barges, tugboats and other vessels, Deepwater Wind began installing the foundations in July. With the first 400-ton steel jacket piled onto the sea floor, the company is officially moving ahead with development after years of delays and legal battles pushed other offshore wind farms to the brink. Perhaps most notably Cape Wind, which missed deadlines and became engulfed in litigation during its 14-year push to build a 130-turbine wind farm off the coast of Massachusetts.

“Offshore construction is now well underway on the Block Island wind farm,” Deepwater Wind CEO Jeff Grybowski said in a statement. “We know the world is watching closely what we do here, and we’re incredibly proud to be at the forefront of a new American clean-tech industry launching right here in the Ocean State. We’re confident it’s just the start of something very big.”

Meanwhile, President Barack Obama’s administration has pushed initiatives to promote clean energy through the Clean Power Plan. Unveiled this year, the plan aims to reduce carbon dioxide emissions by 32 percent below 2005 levels over the next 15 years at the country’s power plants. It also calls for increasing renewable energy production by 30 percent while cutting costs associated with it.

After years of false starts, the federal government stepped in last year to try to speed up the pace of offshore wind development. The U.S. Department of Energy announced plans to provide up to $47 million apiece to three wind projects that sought to build farms off the coasts of New Jersey, Oregon and Virginia. Despite the help, the efforts largely have stalled in light of legal and financial challenges.

Keystone’s innovative twisted jacket design is slated to be used on two of the projects.

The design gained industry attention after it was named a finalist among more than 100 entries in Carbon Trust’s 2011 Offshore Wind Accelerator competition, which was held to promote less expensive wind turbine designs.

In Block Island, the jackets are attached to the seabed with piles. Each structure is up to 108 feet tall and weighs nearly 380 tons. The platforms add another 50 feet and 340 tons. Once it’s assembled, the turbine’s hub is almost 330 feet above the platform, and its blades stretch up to 270 feet long.

Ben Foley, who heads Keystone’s offshore renewables unit, said he’s optimistic that the U.S. will make bigger strides in offshore wind-power production in coming years.

“Globally, everything’s just kind of slowed down, but now we see it turning the way we hoped it should,” he said, noting that 15 percent of Keystone’s revenue is driven by offshore renewables. The company has 300 employees.

Designing the wind farm’s foundations required some adjustments from building for an offshore oil and gas platform, such as taking into account the added strain from the steady, repetitive vibration from the spinning turbine.

“Every time a blade goes past 12 o’clock, it’s picking up a maximum load,” said Zach Finucane, Keystone’s manager for Block Island, “and when it’s down at 6, it’s picking up a minimum load.”

Keystone engineers ran thousands of tests to ensure that the design would hold up under various weather conditions and load scenarios. Each calculation was done multiple times. Altogether, nearly 10 million tests were completed.

At Gulf Island, which began work on the structures early this year, workers relied on many of the same concepts they’ve used to build marine structures for the Gulf’s oil and gas industry. “There was a little bit of difference in terms of how the foundation mounts for the turbines themselves,” Meche said.

It took almost two months to build each jacket. The structures were delivered to Rhode Island by barge, and each trip took about two weeks, depending on the weather.

“This is really a test project of sorts to see if the energy can be produced at a reasonable rate for customers, and so I think this is the start of something that can really be a big segment of our business going forward,” Meche said.

The National Renewable Energy Laboratory, a federal research lab, estimates that the U.S. has 4,200 gigawatts of offshore wind potential that’s within reach, compared with 11,000 gigawatts of onshore wind potential.

Offshore wind is attractive to some clean energy advocates because the massive turbines can use more consistent winds blowing over the ocean. That leads to more power that can be generated than from similarly sized turbines installed on land.

But the extra potential comes with a catch, the federal Energy Information Administration noted last month as construction began on Deepwater Wind: Offshore turbines are far more expensive to build and maintain.

Still, offshore wind development has grown in Europe, which last year had 90 percent of the estimated 8.8 gigawatts of the world’s installed capacity. The first offshore turbines were installed off Denmark’s coast in 1991, although it took another decade before it gained much headway.

Industry analysts believe the long-term success of offshore wind development ultimately will hinge on whether developers can lock up long-term contracts to market the electricity — an often difficult hurdle to clear but one that Cape Wind had overcome until National Grid and Eversource Energy canceled pacts this year to buy a majority of its output.

“So far, the high cost of domestic offshore wind projects has made them economically unattractive, despite the availability of federal tax incentives and state policies to promote use of renewable energy,” the EIA, the Energy Department’s statistical arm, said Aug. 14. “In contrast, onshore wind capacity has grown by more than a factor of 25 since 2000.”

Many experts, including David Dismukes, head of the LSU Center for Energy Studies, expect wind power will continue to face financial hurdles for the near future. But if it catches on, Dismukes believes Louisiana’s oil and gas industry will have a natural advantage for its experience designing and building marine structures.

“They certainly have the technical know-how and the ability,” he said. “We’re always well-positioned for something like that. It’s just a matter of whether the market can sustain that or not.”

Meche, of Gulf Island, believes offshore developments will need to show larger returns than what’s expected near Block Island before it gets a serious look.

“You’ve got five platforms out there trying to generate 30 megawatts of power,” he said. “When we talk about trying to generate 250 to 300, a lot of people start paying attention.”

Follow Richard Thompson on Twitter, @rthompsonMSY.