New offshore wind farms are under construction around the globe. However, the installation of the state-of-the-art foundation - impact driven monopiles - often causes very high underwater sound pressures. Due to regulations in many countries, solutions to mitigate sound emissions are required. Several approaches to mitigate the pile driving noise in the water column that surrounds the pile exist and are often applied. However, modifying the sound source instead, i.e. pile and hammer, to reduce the noise already at the source before it is emitted into the water column, has recently become of interest.

This paper presents a hammer that is designed to cause significantly less sound emission than state-of-the-art hammers. A prolongation of the ram impulse due to temporarily stored energy inside the hammer components, i.e. a slower transmission of the ram energy to the pile, is the key to the reduced sound emissions. However, sound reduction also depends on the pile geometry. Overall, the results show that taking the sound emissions already into consideration while designing the hammer, the pile and possible additional parts included in the installation process, has a lot of potential to reduce the underwater sound levels during offshore pile driving.

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