Van Oord installs world’s first submerged Slip Joint successfully

On 25 April, the Slip Joint foundation was successfully installed at the Borssele Wind Farm Site V.

Van Oord installs world’s first submerged Slip Joint successfully
Photo: Van Oord

It is the first time anywhere that a submerged Slip Joint was used on a full-sized offshore wind turbine on a fully commercial basis.

After years of developing the system in cooperation with its technology partners, Van Oord deployed offshore installation vessel Aeolus to install the Slip Joint foundation this week. The design and production of the Slip Joint was certified by DNVGL in the autumn of 2019, with MottMcDonald assessing it on bankability aspects. The Borssele Site V project consists of two 9.5 MW wind turbines and Van Oord has been awarded the Balance of Plant scope for this project.

The Slip Joint is an alternative connection between foundation elements, a monopile and a transition piece. It consists of two conical sections placed on top of each other. The Slip Joint is based on friction, with the weight ensuring firmness and stability. Installation takes place by sliding the wind turbine’s foundation elements over the monopile, without having to use grout or bolts.

Unlike standard solutions, the Slip Joint makes a submerged connection possible, allowing for a more balanced weight distribution between monopile and transition piece. It therefore opens up the possibility of manufacturing larger foundations for the next generation of wind turbines with existing manufacturing facilities and installing them at deep-sea locations using existing vessels. The (conical) sections that make the connection are produced using standard manufacturing methods. The Slip Joint provides a rapid, simple and safe installation solution in combination with reduced maintenance for the duration of the project.

The Borssele Wind Farm Site V is a new sustainable energy zone some 20 kilometres off the Dutch coast, which is designated as an innovation site within the Borssele Wind Farm Zone. Two Towers BV, consisting of Van Oord, Investri Offshore and Green Giraffe, has been awarded the project and given a unique opportunity to introduce advanced technologies for commercial application in future offshore wind farms with larger turbines and in deeper waters and to demonstrate the practical value.

The other technologies demonstrated at the Borssele V Site are Thermally Sprayed Aluminium (TSA), Impressed Current Cathodic Protection (ICCP) optimisation, oval cable entry holes and Eco-friendly scour protection. By demonstrating these technologies, the Borssele V Site contributes to decreasing the Levelized Cost of Energy (LCoE) of offshore wind energy.

It is therefore expected that the demonstrated innovations will set a new standard for future foundation designs. The project was only possible through close cooperation between government, industry and scientific research institutes. Once operational in 2021, the 19 MW offshore wind farm will provide sustainable energy to 25,000 households.