Reducing Vessel Strike Risk During Offshore Wind Operations

Service vessel docking at an offshore wind turbine

By hosting technicians overnight, service operating vessels can travel at slower speeds and reduce the risk and severity of vessel strikes

Credit: Adobe Stock (standard license)

Vessels that accommodate technicians at-sea during the operations and maintenance phase of offshore wind energy projects offer an elegant solution to arguably the most significant potential impact of offshore wind development on large whales: deadly vessel strikes.


Vessel strikes pose a serious threat to whales. They are one of the main factors currently driving the North Atlantic right whale to extinction and are also implicated in the ongoing Unusual Mortality Events for humpback whales and minke whales. Vessels of any size can seriously injure or kill a whale, and the probability of a deadly vessel strike increases when vessels are traveling at speeds faster than ten knots.

Three right whale calves have been lost to vessel strikes within the last two years. The serious injury and likely death of a calf was reported in January 2020 and two calves were documented to have been killed in June 2020 and February 2021. One of the calves’ mothers was also seriously injured at the time of the strike and another hasn’t been sighted since the strike occurred. North Atlantic right whales cannot withstand even a single of death from human causes per year if the species is to survive. Every vessel traveling at speeds above ten knots poses an unacceptable risk.

Offshore wind energy holds great promise in bringing clean, renewable energy to America’s shores and supporting thousands of well-paying jobs in both coastal and inland communities. The Biden-Harris administration has set forth an ambitious and necessary goal for the nation to have net-zero global greenhouse emissions by the middle of the century, and committed the U.S. to reducing net greenhouse gas emissions by approximately half 2005 levels by 2030. Offshore wind energy is one of the most abundant sources of zero emissions energy and must play a significant role in our clean energy portfolio if the nation is going to meet its goals.

The development of offshore wind energy, like any development activity, poses some risks to the environment that need to be avoided, minimized, and mitigated. An increase in vessel traffic during the construction of offshore wind projects as well as during their approximately 30-year operations period will elevate the risk of vessel strikes both at the offshore wind project site and the transit lanes to and from the port.

Traveling at ten knots or less can be especially challenging during the long-term operations of the project if maintenance crews need to travel quickly to and from the offshore wind project site and maximize the number of turbines maintained during daylight hours. The vessels responsible for transferring crew to and from the port are expected to regularly travel at speeds of 20 knots, adding to an already unacceptable level of risk.


North Atlantic right whale and calf

Three North Atlantic right whale calves have been killed by vessel strikes in the last 18 months. Slowing vessels down will help protect them.

Credit: Credit: Florida Fish and Wildlife Conservation Commission. NOAA Permit #20556-01.

How do we mitigate the risk of vessel strikes and protect whales while still advancing offshore wind?

One important solution exists in the form of Service Operating Vessels (or “SOVs”) - larger multifunctional vessels that serve as a kind of “at-sea base” that accommodates technicians for days or weeks at a time, transferring them, and any necessary tools and parts, directly to and from individual wind turbines. Because the vessels spend multiple days at sea, they are not under the same time pressure to return to port and can travel more slowly to and from the offshore wind site. SOVs also increase the efficiency of maintenance activities and, by traveling more slowly, may reduce emissions and vessel noise.

The benefits of SOVs are gaining traction among the offshore wind industry. Equinor has committed to use an SOV during the operation of the Empire Wind project that is scheduled to start generating power in 2023. Empire Wind is located in the New York Bight where numbers of large whales have been increasing in recent years and spectacular aggregations of humpback, fin, and minke whales—comparable with those observed at the Stellwagen Bank National Marine Sanctuary—gather to feed during the summer and fall. Equinor recently made a similar commitment for the first two operational phases of its Dogger Bank wind farm offshore the United Kingdom, touted to be the largest offshore wind energy project in the world when complete in 2026.

Ørsted—the largest lease holder in the U.S.—and partner company Eversource recently signed a long-term charter agreement with Edison Chouest Offshore (ECO) for the provision of the first-ever US-flagged SOV. The SOV will be engineered, constructed, and operated by ECO as an integral part of the operation and maintenance of the Revolution Wind, South Fork Wind, and Sunrise Wind projects in the northeast U.S., pending permitting by the Bureau of Ocean Energy Management (BOEM). These projects are located within and close to an extremely important year-round foraging area for North Atlantic right whales. The use of an SOV that can house offshore wind workers will offer essential protection to this critically endangered species. Orsted’s SOV decision will also generate more than 300 construction jobs in Florida, Mississippi, and Louisiana to build the new ship.

SOVs help advance offshore wind energy development, while providing a solution to one of the most serious impacts to marine mammals. As this new wind energy industry takes off, we encourage developers to seek out technologies like these to help mitigate additional pressures on our ocean life.

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