Due to currents at the anchoring point of the monopiles in the seabed and thus risk of erosion, stones are dumped on the seabed to limit the movement of the sand. The stones are imported from Norway. 

The picture shows the stones which are to be placed on the seabed to stabilise the basis. 

Once the foundation is ready, a conical hollow steel monopile is driven into the seabed.

The monopiles have a diameter of 3.9 metres and a length of 30-40 metres. The length depends on the exact position on the offshore bar. A steel monopile is being loaded on board the vessel in the port. The yellow pillar at the rear is the transition piece. In front to the left (with hydraulic pipes and a capital M painted on it) stands the hammer that drives the monopile into the seabed.

 
The top of a transition piece

The transition piece is pulled over the monopile and is pre-installed with features such as boat landing arrangement, safety fence, etc. The fully mounted platform is located 13 metres above sea level. The monopile is made of steel, whereas the platform is made of concrete.

Due to currents at the anchoring point of the monopile in the seabed, stones are dumped on the seabed to limit the movement of the sand. The stones are imported from Norway.

 
As illustrated, the lower pile cannot be seen from the sea level.