Michel Kurstjens, Product Strategy Director

Skybox: slip joint connection for secondary steel

Sif uses new technologies and smart solutions to take the market to the next level and reduce the costs of wind energy. There’s also a need for this: to remain competitive with other energy sources (without the need for subsidies), the costs of the entire chain must be reduced and revenues increased. The Skybox is one of the cost-saving innovations.

About a year and a half ago, Michel Kurstjens saw that many of our customers were shying away from a transition piece with secondary steel (ladders, boat landing, and main access platform) and instead choosing a direct bolted connection of the tower on a monopile with brackets where the secondary steel can be hoisted offshore. This saves costs, because no transition piece is needed, but is time-consuming in terms of installation and awkward in terms of manufacturability. The manual welding of the brackets on the monopile is a huge interruption to our production flow. ‘This can be improved’, Michel thought, so he sought the help of Sif's designers.

Three challenges

‘I gave Sif's designers three conditions that the new solution had to meet. First of all, there should be no brackets on it. The second condition was that only one hoist should be needed offshore. And thirdly, the solution should be installed by floating vessels with a dynamic positioning system (DP) and without anchors – the installation vessels of the future,’ says Michel.

What's the Skybox?

Sif's designers worked together with DOT (Delft Offshore Turbines) and consulted with technicians. The result is the Skybox! ‘The Skybox is a connection between the monopile and the tower that slides over the monopile with a Slip Joint Connection. The Skybox uses the Slip Joint Technology to install the secondary steel on the monopile with one offshore hoist. The use of a catcher plate at the bottom of the Skybox makes it suitable for DP installation vessels. It is a new application of Slip Joint Technology. DOT has developed the Slip Joint Connection to slide the tower directly onto the monopile.