The first phase wind turbines are built on gravity-based foundations while phase 2 and 3 are built on Jacket foundations.


Jacket Foundations (Phase 2&3)


Gravity Based Foundations (Phase 1)

Jacket Foundations (PH2&3) Jacket Foundations (PH2&3)   Gravity Based Foundations (PH1) Gravity Based Foundations (PH1)
The jacket foundation is a steel structure with four legs connected to each other with braces. The legs are grouted to pinpiles. The latter are driven into the sea soil. The main advantages for the jacket foundation in comparison with the gravity based foundation is serial production and easier logistics.
The gravity based foundation (GBF) is a concrete cylindrical/conical structure. It is a support structure held in place by its own gravity. 
The deepest locations realized with GBF foundations are the ones at the Thorntonbank. 
  • Faster fabrication (serial production)
  • Better quality control (7/7 days – 24h/days)
  • Simpler logistic
  • Less harbour space needed
  • Less marine preparation works
  • For the Jacket installation, only 2 types of installation vessels are required. One for the pre-pilling with small dimension piles and readily available pile driving hammers and another one for the installation of the jacket foundation (delivered to the site directly from the jacket production line)
  • More cost-effective (steel price evolution!)
  • Easier decommissioning
  • Need for further standardization and industrialization
  • Man power-intensive works
  • Logistically complex
  • More harbour space needed
  • Many marine preparation works (seabed preparation, scour protection, …) subject to weather risks
  • The installation of the GBF requires the intervention of numerous large vessels, subject to weather risks

Jackets are standard equipment in the Oil & Gas offshore industry and are state-of-the-art technology for North Sea conditions. They are increasingly seen as one of the standard foundation designs for offshore turbines in mid-depth waters (25-50 meters) and have been utilized recently for a number of projects, including Beatrice and Alpha Ventus with Senvion turbines.