The waters off the coast of New England have gotten noisier in the last year as the nation’s first-ever large-scale offshore wind farms began pile driving steel turbines into the ocean floor.
But developers say they have a way to blunt the deafening sound for whales, dolphins and the endangered species of the northern Atlantic: blowing bubbles.
“Pile driving in the ocean is very, very noisy,” said Richard Hine, whose maritime company ThayerMahan Offshore is the first U.S. firm to pilot “bubble curtains” for wind turbine construction. The walls of air bubbles help absorb sound energy. “You can knock out about 80 to 90 percent of the acoustic energy and get it below levels where they’re harmful to marine mammals,” Hine said.
Bubble curtains are one way the rapidly expanding offshore wind industry is trying to mitigate its potential harms as it grows off the nation’s coasts. The work may be more critical than ever for wind developers over the last year, following a spate of whale deaths on the Eastern Seaboard that sparked harsh accusations against the nascent industry from Republican lawmakers and beach homeowners.
Though experts have blamed ship collisions, an exploding humpback whale population and fishing entanglements for the deaths, the mortalities drew an unwelcome spotlight to the first massive offshore wind arrays in the nation’s history.
And much more offshore wind construction is on the horizon.
The Biden administration has committed to approving 16 offshore wind farms by 2025, with the hopes that developers will build enough wind turbines by 2030 to power 10 million homes. The powerful offshore power plants are key to nearing national and state climate goals from New York to California. In total, the boom of wind farms will require thousands of turbines to be fixed to the ocean floor.
The nation’s first two large-scale offshore wind farms — Vineyard Wind and South Fork Wind— are under construction off the coasts of Rhode Island and Massachusetts. Both of those projects are using double bubble curtains during turbine installation to mute the sound.
“We hope that by pioneering this technology that it will become standard practice for the industry going forward,” Vineyard said in a statement.
To create the bubble curtains, steel encased, perforated, rubber hoses are sunk to the seafloor in two concentric rings around a monopile. As sound waves pulse out during pile driving, that sound energy must travel through the two walls of air, greatly reducing their impact.
“When you have large density changes, like from water to air, it mitigates a lot of the sound,” Hine said.
ThayerMahan vessels carry a suite of powerful air compressors to create the bubbles. At Vineyard, a crew of just under 30 — including union deck crews based in New England — ramp up about 30 minutes before pile driving begins. That’s how long it takes to create suitable air barriers. Throughout the pile driving, the vessels are also monitoring the sound levels to gauge how much sound is getting thorough the curtain.
Pioneered in Germany to protect marine life in the North Sea, bubble curtains are most effective in shielding animals that rely on lower frequencies to communicate, like baleen whales. The so-called gentle giants of the ocean, the species include the blue whale, the humpback whale and the critically endangered right whale, Hine said.
“Whales are a sensitive topic for the wind industry,” he said. “It’s a key part of safely installing wind turbines and doing it in an environmentally sensitive way where you’re not killing mammals and fish.”
The bubble curtain technology is also somewhat effective for high frequency sound mitigation, helping mammals like porpoises and dolphins.
ThayerMahan was developed by Hine and his partners, two former submariners.
They launched the Groton, Connecticut-based company in 2016 and specialized in deploying unmanned underwater vehicles, essentially underwater drones, or robots. A portion of their business was devoted to defense contracts with the U.S. Navy. They detect shipwrecks in the sand and abandoned torpedoes on the seafloor.
As offshore wind began to expand in the U.S. during the Trump administration, wind companies began percolating in New England towns, setting up their U.S. offices, investing in infrastructure like Connecticut’s New London Pier and crossing paths with local firms like ThayerMahan.
“The largest wind company in the world kind of air dropped into New London,” Hine recalled of connecting with Denmark’s Ørsted. “They said, ‘Hey, if you guys can detect submarines and destroyers and stuff, can you detect whales?’”
ThayerMahan said it could. The company developed a monitoring system that can detect the type of whale in the vicinity by identifying their unique sound, from the swooping tones of an elevator going up on a spaceship that the Atlantic right whale makes to the haunting cry of the humpback.
Over time, ThayerMahan expanded their offerings according to what the industry needed — like surveys of the seafloor before laying cables and bubble curtains.
ThayerMahan is partnered with the world leader in bubble curtain technology, the Germany company Hydrotechnik Lübeck, to bring the industry to the U.S.
Big bubble curtains are not specifically required in the U.S., but they are an accepted option to meet federal sound control requirements set by the Bureau of Ocean Energy Management.
To meet BOEM’s requirements, Dominion Energy, the utility behind the largest approved offshore wind project in the country, will be using double bubble curtains for its monopile installation off the coast of Virginia Beach.
The company tested the bubble curtains in 2020 when it partnered with Ørsted to install a two-turbine pilot project. To compare impacts, one turbine was pile driven using a bubble curtain and the other without.
“The sound levels were reduced by the bubble curtain between 11 and 23 decibels, depending on distance and sound frequency,” said Jeremy Slayton, a spokesperson for Dominion.
Pile driving sound data was also collected at the Block Island Wind Farm, a five-turbine pilot project built in 2015 off the coast of Rhode Island that was the first offshore wind farm in the U.S. During pile driving, sound was recorded at roughly 500 meters and far from construction, roughly 15 kilometers.
Vineyard said it has experimented with different sound-dampening options and found that a double bubble curtain like ThayerMahan’s can be combined with a hydro sound damper — a related sound system that uses nets — to get the strongest result. That approach is being used on its 62 turbines off the coast of Martha’s Vineyard.
ThayerMahan is not the only company doing bubble technology in the U.S. But it is the first U.S. company to do the work.
Sam Salustro, vice president of strategic communication at the offshore wind supply chain group Oceantic Network, said ThayerMahan is a good example of the economic ripple effect expected from the offshore wind industry.
Offshore wind has been promised by politicians and policymakers as a massive job creator. Many of the jobs are indirectly related to the wind power generation itself, in ship building, manufacturing and construction, Salustro said.
“The fact is that most of the job creation will occur lower or deeper into the supply chain and away from the project development sites,” Salustro said.
Though the offshore wind industry is expected to create new companies, it’s also going to drive expansion in existing companies, like Great Lake Dredge & Dock, a company founded in 1890 that is building an offshore wind vessel in Philadelphia, Salustro said. The first turbines installed in the U.S., at Block Island, depended on oil and gas lift vessels for the offshore oil and gas industry, based in the Gulf of Mexico.
Hine is also chartering service vessels from the Gulf oil industry to carry the compressors that create the bubble curtains. He said moving into the offshore wind arena helped triple the company’s revenue this year, and he expects it to double again next year.
“This is the nature of the big bubble curtain business,” he said.