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Reviewed by: Jennifer Amaral
Last Update: November 13th, 2020
At the 17th Ronald C. Baird Sea Grant Science Symposium Session #3: Sediment and Sound, Jennifer Amaral (Ph.D. student, URI Ocean Engineering and Lead Scientist & Engineer, Marine Acoustics, Inc.) explains what the major differences between monopile and jacket offshore wind structures and how the sound generated from the construction of each varies.
Jacket structures, which were used for the Block Island Wind Farm (BIWF), are offshore wind structures that consist of four corners which are pinned to the seabed with 3 piles each. Monopile structures, which were used for the Coastal Virginia Offshore Wind Project (CVOW), constructed in May and expected to be operational by Fall 2020, consist of one single steel pile that is driven directly down into the sediment.The foundation type that is chosen depends on parameters such as the water depth, seabed properties, and turbine size.
Monopile structures use larger diameter piles than the jacket structures with the BIWF using 50-inch diameter pin piles and CVOW using one 26-foot diameter pile. Both foundation types were installed using impact pile driving, which produced high-level impulsive sounds that were detectable at long ranges from the installation sites. The overall installation time for a jacket foundation at the BIWF was longer than the installation time for a monopile foundation. The jacket structures consisted of four legs that required three pile sections to be driven in each leg, whereas the monopile only required installation of a single pile. Each pile section at the BIWF was installed in about 1 hour with the hammer hitting the top of each pile every 1 to 2 seconds. The installation of a single monopile at CVOW was completed in roughly the same time (1 hour).