Bluestream has worked with Wageningen Marine Research (WMR) to develop a remotely controlled Marine Growth Sampling Tool to survey marine growth on offshore wind turbine foundations in the North Sea. In the early stages of colonisation, algae and small sea creatures attach to the foundation surface, with numbers increasing over time. Such surveys were previously carried out by SCUBA divers. Vattenfall provided access to one of the Hollandse Kust Zuid wind farm foundations for the study. The foundation became available after the Julietta D vessel collided with it during a storm in January 2022, rendering it unusable for turbine installation. While the turbine was removed, the foundation was left in place.
For WMR, it was essential that the tool could scrape a consistent surface area to quantify total marine growth. For Vattenfall, it was important that the tool did not damage the foundation coating. Tests were conducted with scrapers made from polyurethane and metal. The polyurethane scraper performed well and carried a much lower risk of damaging the coating.
WMR measured the number, length, and width of coating particles collected. As particle thickness could not be determined in the laboratory, samples are undergoing further analysis. Only small amounts of coating residue were found, amounting to less than 1/20,000th of the sampled area.
Of 25 tests, 21 were successful. The growth observed on the foundation was relatively uniform and consistent with samples previously taken from other North Sea foundations. Amphipods, small shrimp-like crustaceans between 0.5 and 20 millimetres in size, dominated the samples, covering most of the foundation surface at densities of tens of thousands per square metre. As the foundation has only been in place for a few years, the growth layer was still thin. Over the next decade or two, a more diverse range of species is expected to establish.
The project was completed earlier this year and Bluestream and WMR plan to continue their collaboration with the development of a new tool designed to collect samples from scour protection layers that shield the seabed from erosion.
Photo: Bluestream
