Floating wind turbine off Naples stayed quieter than surrounding ships, waves and the sea’s natural animal sounds

The turbine itself was not the noisiest item in the water.

In the waters off Naples, an underwater microphone listening near the Hexafloat scale model created by Saipem registered ship noise, wave noise, cracking crustaceans, singing fish, and clicks from passing dolphins.

However, the turbine itself was registering noise as well.

Hexafloat prototype testing was performed from September to December 2023 by means of an automatic underwater recorder located about 98 feet away from the turbine.

But even after the researchers were able to filter out the other sounds being emitted from the test site, the added noise from the turbine was less than that coming from the marine environment itself.

One recorder sat 98 feet away

Hexafloat prototype testing was performed from September to December 2023 by means of an automatic underwater recorder located about 98 feet away from the turbine.

The device was quite small in comparison with a typical commercial offshore turbine.

The prototype was about 33 feet tall and had blades 21.3 feet long located at a distance of about 328 feet from the Naples harbor pier.

This created many problems in terms of the acoustic monitoring system used.

There were large cargo vessels, ferries, hydrofoils, fishing boats, and pleasure craft that constantly cruised the area.

Wind and waves only added to this problem.

And then came the animals to create noise too.

The sea already had its own soundtrack

Manually checked recordings revealed intensive biological noise.

There were repetitive crustacean snapping noises from shrimp.

The fish generated choruses.

The delphinids were picked up less often via echolocation clicks.

These noises occurred in the same waters with a functioning floating wind power plant.

It is important to note that the measurement of the turbine noise is not so simple that one puts a hydrophone near the device and measures the total intensity of the noise.

Most of the noise detected may have come from another source.

Therefore, the scientists divided periods by month, time of the day, wave height, and the operational state of the turbine.

The turbine lived mostly below 1 kilohertz

After taking these other sources into consideration, however, there was still a traceable mark left by the Hexafloat.

Much of the noise created by the turbine occurred under 1 kHz.

When waves were less than 3.3 feet, operation of the wind turbine increased sound levels in the 63 Hz and 125 Hz third-octave bands by 4 decibels.

With maximum blade speed, however, another characteristic was observed.

A clear tonal signal was observed at 400 Hz.

In certain cases, where matched conditions existed, the difference between the highest operating condition and stopping was more than 8 dB.

Nevertheless, shipping and wave noise were still the dominant sound sources.

The rotor was traceable.

It was not, however, an acoustic master.

The chains made a different sound

Floating wind provides hardware components that the bottom-fixed turbine lacks.

It requires anchoring through the mooring systems, which respond to movements caused by the wind and waves acting on the structure.

At Hexafloat, those metal chains have had their say.

They observed short broadband emissions centered at 3 kHz and tonal emissions up to about 8 to 10 kHz.

These signals seemed to correlate with movements of the floating structure and variations in wind and waves.

This provides two sources of acoustic emissions for floating wind.

The turbine equipment emits its typical low-frequency humming sound.

The responding moorings may add to the signal with high-frequency components.

A prototype cannot answer the wind farm question

The levels measured did not indicate any physiological harm to marine life due to the threshold set by the researchers.

However, it does not imply that the sounds are physiologically harmless.

The researchers state that it is impossible to exclude the possibility of masking the communication of fish within the time-frequency overlap between the turbine noise and biological choruses.

There is a further constraint that should be noted.

This is just a scaled-up prototype; not the dozens of full-scale floating turbines operating simultaneously in a wind farm.

More turbines and their mooring system will create a totally different soundscape, and the researchers explicitly point to the fact that more research is necessary for scaling up their findings.

For the time being, Hexafloat gives us something more concrete.

It demonstrates that a floating turbine can become a distinctive mechanical source of sound without being the most prominent sound source in the Mediterranean.

Off Naples, ships and waves won this competition.

All the details of the study can be read here: Buscaino, G., Papale, E., Ceraulo, M., Bardazzi, A., Lucarelli, A., Gao, R., … & Lugni, C. (2026). Acoustic Impact of a Floating Wind Turbine Prototype in the Mediterranean Sea. In The Effects of Noise on Aquatic Life IV (pp. 1-13). Cham: Springer Nature Switzerland.