Slow Mill tests innovative anchor for wave energy
What if sustainable energy from waves at sea becomes feasible with a system that is easy to install and remove? With that question, start-up Slow Mill signed up for the Deltares SME Challenge. By taking part in the challenge, start-ups and SMEs have the opportunity to test their innovative design concept in Deltares’ experimental facilities, guided by experts in the field.
Sign up now for the SME Challenge autumn edition 2026!
Slow Mill is working towards a sustainable future in which energy is generated from waves at sea. Since its founding, the company has been developing a wave energy generator in combination with an innovative anchoring system. That anchor plays an essential role: it must keep the installation stable in position while remaining practical and cost‑efficient to install.
Following earlier tests in the North Sea, during which electricity was generated for the first time, a key challenge emerged. Erosion of the seabed occurred around the anchor, potentially reducing the system’s stability. Participation in the Deltares SME Challenge gave Slow Mill the opportunity to investigate how the anchor design could be adapted to limit this erosion and make the system more robust.
Research in the Atlantic Basin
Guided by Deltares experts, Slow Mill tested various anchor designs in the Atlantic Basin. In this facility, flow conditions can be accurately replicated, providing insight into the interaction between the anchor and the seabed.
The experiments examined the impact of shape on the flow around the anchor and the extent of scour. By testing different geometries, it became clear which designs result in smaller scour depths and volumes. These insights are crucial for developing a stable and reliable anchoring system.
In addition to the anchor’s shape, the role of roughness and biofouling was also investigated. In practice, the anchor was quickly colonised by marine life. Rather than preventing this, Slow Mill has embraced it in a nature‑inclusive design. With so‑called ‘eco patches’ – structures with openings and cavities – space is created for organisms such as small fish, crabs and sea anemones.
This growth increases surface roughness and slows the flow around the anchor, helping to reduce erosion. Initial results show that this combination of shape and nature‑inclusive design can contribute to a more stable position on the seabed.
We observed that the anchor naturally becomes overgrown with marine life. We have embraced this in our design. With this nature‑inclusive approach, we not only improve stability but also develop a more sustainable solution for offshore energy.
Erwin Meijboom, co‑founder and director of Slow Mill
Smart installation and cost savings
The anchor is designed with simple offshore installation in mind. The system is connected to the wave energy generator in the harbour and then towed to sea as a single unit. By filling the anchor with air, it floats during transport. At the installation site, it is filled with water, after which it sinks in a controlled manner into position.
This method eliminates the need for heavy crane vessels and diving operations, making installation faster and more cost‑efficient. In addition, the system can be removed just as easily using the same method.
Step towards long‑term testing at sea
The insights from the Atlantic Basin provide direction for the next phase: long‑term testing at sea. Whereas previous trials were short‑term, Slow Mill is working towards a test period of approximately one year.
For this, it is essential that the anchor remains stable under various conditions. The experiments at Deltares clarify the design choices required and provide concrete guidance for further optimisation.
This type of subsea anchor is still relatively uncommon, so this project also delivers new insights for us. We are learning how shape and flow interact and how we can limit erosion.
Minghao Wu, expert offshore scour and scour protection at Deltares
Thanks to the SME Challenge, Slow Mill gains access to facilities and expertise that are normally unavailable to a start‑up. The combination of experiments and expert guidance helps to quickly understand what does and does not work in practice.
New insights for offshore wave energy
Initial results show that design, flow and ecology are closely interlinked. By combining these aspects, a more robust solution for offshore energy generation emerges. This opens up prospects for the further development of wave energy as a sustainable energy source.
This case fits well with Deltares: testing innovative solutions for complex water and energy challenges, and supporting entrepreneurs working on sustainable applications with societal impact. The Deltares SME Challenge provides space to test new ideas under realistic conditions and to develop knowledge that advances the sector.
Register for the SME Challenge autumn 2026
Slow Mill’s experience shows what participation in the Deltares SME Challenge can deliver: insight into what works, clarity on next steps and a tangible step towards real‑world application. Registration for the SME Challenge 2026 opens (insert date). Start‑ups and SMEs with an innovative design concept in the field of water and energy are invited to apply and take their idea further.
There is active engagement in shaping the design of the test, and Deltares’ expertise is being brought in. I also notice a great deal of enthusiasm, as we are genuinely working on something new about which little is yet known.
Erwin Meijboom, co-founder and director of Slow Mill
Interested in applying?
Sign up now for the SME Challenge autumn 2026!
