Three marine vessels that study the makeup and geology of seabeds are scheduled to arrive in Maine over the next week or so to survey the proposed route of an underwater cable that will link a floating, offshore wind turbine near Monhegan Island with the mainland power grid in East Boothbay.

The vessels are scheduled to be on site next Monday through April 4, weather permitting. They are planning to conduct three passes along the 23-mile route, as well as study the area where the turbine will be anchored in state waters south of the island.

The vessels also will perform an assessment around Mack Point in Searsport, where the floating, concrete platform that supports the turbine could be fabricated.

The subsea cable survey marks a milestone for New England Aqua Ventus, the partnership that’s developing what is expected to be the nation’s first demonstration of commercial-scale, offshore floating wind technology.

“It’s the first real tangible, physical evidence of offshore wind development activities off the coast,” Chris Wissemann, chief executive of Aqua Ventus, told the Portland Press Herald on Monday.

The survey work is the latest indication that, after a dozen years, a full-size version of the platform technology designed and tested at the University of Maine will finally get in the water. Developers plan to begin construction in 2022 and have the turbine in service in 2023. The cable also will likely be laid in 2023.

Developers say the test project is expected to generate more than $125 million in total economic activity and create hundreds of Maine-based jobs during the construction period.

The project received a major boost last August when Diamond Offshore Wind, a subsidiary of Mitsubishi Corp., and RWE Renewables, the world’s second-largest offshore wind company,  joined the public-private partnership and committed to investing $100 million. That investment comes on top of $47 million in grants already awarded by the U.S. Department of Energy.

Last November, the partnership created an online portal to start lining up vendors and suppliers.

The cable survey also is significant because it will be an early indicator of the degree to which fishing interests can coexist with a new, evolving energy industry that will competing for sea bottom off the coast of Maine.

Fishing interests already feel under pressure from a variety of forces, from right whale protection mandates to shifting lobster export markets, according to Ben Martens, executive director of the Maine Coast Fishermen’s Association.

“It’s clear that Maine wants to be a leader in this space, floating wind technology,” Martens said. “But the concerns are very real for the fishing industry; (it’s) kind of being pushed to the side for something else.”

Aqua Ventus has been in contact with fishing interests this winter to brief them on the path and work schedule. It intentionally chose to work in March, despite the greater potential for bad weather, because there are no conflicts with recreational boaters and fewer lobstermen working traps.

The partnership has told fishermen that gear in the path of the survey vessels will need to be removed before work begins. It has published information listing the coordinates of cable and anchor survey locations. Any gear that becomes entangled during the survey will be turned over to the Maine Marine Patrol, the developers say.

Martens said it has been challenging to engage fishermen and exchange data during the coronavirus pandemic, leaving much of the information-sharing to virtual meetings. That has left questions unanswered about the potential impact the cable work will have on certain fisheries, such as scallop harvesting.

“I think there’s still a lot of misinformation out there,” he said.

Wissemann said the partnership intends to bury the cable along its entire 23-mile route, which could mitigate some of the concerns among fishermen. In that regard, he said, it would be no different than other undersea electric cables currently connecting Maine islands, such as one from Rockport to North Haven that was buried six feet under the mud of Penobscot Bay in 2005.

Once the cable comes ashore in East Boothbay, it will be routed underground to a Central Maine Power substation in Boothbay Harbor. The seabed survey will be conducted by vessels owned by Fugro Marine USA. They will use the 45-foot R/V Westerly, the 144-foot R/V Go Liberty and the 250-foot M/V Fugro Explorer. The Go Liberty is likely to dock at the Maine State Pier in Portland this week, Wissemann said.

These vessels will use various technologies, including sonar, bathymetry (depth measurements), core sampling and photography to map the ocean floor to measure the depths and shapes of the underwater terrain. Water depths vary along the route, to a maximum of more than 300 feet near the test site. The goal is the find the best route and installation methods to minimize impact on the environment and fishing, the partnership says.

While the location of offshore wind turbines has gotten a lot of attention from fishing interests worldwide, the siting of the cables that connect turbines to each other and to the mainland has received less scrutiny, according to Annie Hawkins, executive director of the Responsible Offshore Development Alliance, a Washington, D.C.-based national coalition of fishing industry associations and companies.

The network of cables can have a greater impact on fisheries than the turbine towers and anchoring systems, she said, because they cover more sea bottom. The best practice, Hawkins said, is to work with knowledgeable fishermen to find the optimum routes and bury cables fully whenever possible.

Wissemann said the cable being considered for the Monhegan project is being sized only for the 12-megawatt test turbine and isn’t designed to eventually bring power to the island. When the demonstration is finished in 25 years or so, the cable could be removed, if that is deemed desirable at that time.

Information gathered from the survey won’t be finalized until May, he said.

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