A few weeks after the successful load out at Heerema Fabrication Group yard, the steel substructure for the transformer platform Hollandse Kust (West Alpha) will leave the port of Vlissingen over the coming weekend (August 14 or 15).

The jacket will be transported on a floating pontoon to its location some 50 kilometres off the coast of Egmond aan Zee. From 2024 TenneT will be start bringing sustainable wind energy to land via this ‘plug socket at sea’.

Ten months after the start of construction, the large yellow supporting structure, measuring 49 metres high, and weighing some 2,300 tonnes, was placed on a floating pontoon earlier this month. Should the weather conditions at sea not allow for safe transport, the sail away will be postponed until further notice, until the weather conditions allow for safe transport and installation, TenneT said in its statement on Friday.

Under pre-determined conditions such as wave height and wind, DEME’s offshore installation behemoth Orion will lift the jacked while the pontoon is towed from under it. After the exact positioning on site, the steel construction will be placed on the seabed by the ship’s cranes.

At the four corners, the jacket will be secured by means of piles that are driven into the seabed to a depth of more than 50 metres. The piles are guided by large pipes of 10 metres which are connected to the feet of the undercarriage. By filling the space between the piles and the tubes with grout, the connection will be made in such a way that the platform can withstand even the heaviest storm in the North Sea.

Prior to installation, the soil conditions on the site were carefully examined. It was also investigated whether there are any unexploded explosives from the Second World War. Next, the contractor poured a large bed of stones to create a firm and flat foundation. The stones also ensure that the soil under the jacket is not washed away by the flow of seawater. With regular maintenance, the construction has a minimum lifespan of 40 years.

Over the next few years, TenneT will connect offshore wind farms to the onshore electricity grid so that the energy generated can be used. Next year, the ready-made superstructure will be placed on the substructure for the Hollandse Kust platform (west Alpha). The platform will be ready in 2024 and TenneT will use this ‘plug socket at sea’ to bring 700 megawatts of sustainable wind energy onshore. The undercarriage was built by Heerema Fabrication Group in Vlissingen on the instructions of Smulders and EQUANS, who built all the platforms (jacket and topside) for the Hollandse Kust (north) (west Alpha) and (west Beta) projects.