Block ip Trap

Subsea Solutions for US Offshore Wind

21 Jul 2021

By Martin Dronfield

Given the renewed interest from developers to establish a U.S. offshore wind supply chain, and the limited domestic experience, many European suppliers are now looking for the right moment to make their market entry. There are clear benefits for the US in leveraging European expertise and critical factors the industry must get right. 

The United States already has many of the skills needed to develop offshore wind projects; the electricians, the welders, and the marine vessel crews in place simply have not been focused on that purpose. Experience will come quickly with the right European supervision, which must align with the requirements of each state and their respective project pipelines, the supply chain, and the workforce already available locally. Only then should European expertise be used to help bridge the gaps. 

Noise attenuation is one such opportunity. Noise attenuation refers to the dampening of sound to protect marine life. European suppliers, in particular, have unusual experience dealing with unexploded ordnance (UXO) - experience that can help protect the US's diverse marine life. The eastern seaboard is a prime location for fixed bottom offshore wind. It's also home to several threatened or endangered species such as the blue whale, leatherback turtle, and the giant manta ray[1], all of which must be given due consideration to protect them from construction noise. 

James Fisher Renewables Article Image 1Noise attenuation and unexploded ordnance expertise

[Asp1] The use of explosive weapons in the first and second world wars, and the government munitions dumping programs that followed, created a complex challenge for any offshore wind developer seeking to construct a project in the North Sea. Fromphosphorus bombs to torpedoes, there are millions of tons of munitions littered across the sea floor. They pose a problem for any offshore development - communications cables, oil and gas platforms, and offshore wind projects - as each must be detected and carefully neutralized before work can begin. With the need to ensure these detonations do not distress, displace, or disrupt local marine life, Europe became a leader in noise attenuation technologies. 

This comes as good news for US project developers who will face similar challenges. Up until 1970, unknown quantities of munitions were disposed of off the US coast in both documented and undocumented locations. While most munitions were dumped in depths far beyond those reached by offshore wind infrastructure, munitions regularly wash ashore or are dredged up by fishing activities. As such, all US offshore wind projects, including developers and regulators, will need to factor in UXO identification and disposal to ensure project activities will not accidentally trigger an explosion or cause a chemical leak.

James Fisher Renewables Article Image 2Responding to the need to operate more sensitively offshore, industry experts have developed a specialized bubble curtain technology that pumps class zero (medical grade) air through a perforated ring (mounted to the seabed) that encircles the construction zone or unexploded ordnance in a ring of air bubbles. The use of a bubble curtain could halve the sound intensity of pile driving[2] for east coast offshore wind projects. 

A typical bubble curtain project might require 20 to 26 compressors, in groups of five, to feed air through each filtration system, which cleans and conditions the compressed air to ensure it is oil-free before it goes into the sea. To further improve the design, the team innovated a new generation of compressors that have a smaller footprint and are stackable. This stackability means a greater number of compressors can be fitted on deck without compromising power output or risking heat build-up. Not only does this save deck space, it also allows smaller vessels to be used for the job, which positively impacts project costs. [Asp2] 

Further innovations are currently being trialed at Taiwan's largest offshore wind farm, where the team is doubling up the curtains to provide a thicker sound barrier to reduce the impact of the installation of the project's monopiles. The double curtain will be created using a dedicated 'noise mitigation vessel' to create a large bubble curtain around the monopile site. A smaller set up onboard the pile driving vessel will provide a smaller bubble curtain directly around the monopile for additional noise attenuation during the installation of the foundations.

James Fisher Renewables Article Image 4

Coupled with the use of pinging or soft-start pile driving, bubble curtains can significantly reduce the potential for distress, displacement, and disruption to local marine life along the east coast. 

The US offshore wind market has reached a pivotal moment in its history. With an administration that is committed to driving climate action and a wealth of experience to draw from on both sides of the Atlantic, being at the starting line of a new offshore wind market has never looked more exciting.  With careful execution and European expertise to lean on, the east coast could be well on the way to having a fully competent and equipped domestic offshore wind supply chain in the next three to five years; an incredible time savings on the decades it took Europe to develop these same competencies. 

By helping the US to leapfrog many of the offshore wind industry's challenges from the past, not only will US projects benefit from smooth execution, they can also ensure things get done right first time, reducing the risk for both man and the environment.


Martin Dronfield is Special Advisor to James Fisher Renewables, which specializes in the delivery of niche topside and subsea marine operations, engineering solutions, and software systems for the installation and commissioning, operations, and maintenance for new and existing offshore wind farms.

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 [Asp1]Caption: An unexploded ordnance located using WROV forward imaging sonar. Noise attenuation technologies such as bubble curtains can be deployed to minimize the impact of unexploded ordnance disposal on local marine life. 

 [Asp2]Caption: A dedicated noise mitigation vessel (left) encircles the pile driving vessel (right) in a curtain of bubbles to provide noise attenuation during the installation of monopiles for an offshore wind farm. 

Author: Martin Dronfield
Volume: 2021 July/August