23 Giant Concrete Caissons Floated: Princess Elisabeth Island Hits a Critical Build Milestone as North Sea Installation Restarts This Spring

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Jan De Nul Group has completed construction and float out of all 23 concrete structures that will form the base of Princess Elisabeth Island, Belgium’s first artificial energy island designed to connect offshore wind farms in the North Sea.

The company confirmed the milestone in a LinkedIn update posted 39 minutes before publication, stating that the final concrete structure has been constructed and floated successfully. With that achievement, construction work at the Vlissingen site in the Netherlands is now officially finished.

The structures have been moved to the Scaldia terminal for final finishing works ahead of the next offshore installation phase.

Artificial islands are not new, but in offshore wind infrastructure they remain rare enough to turn heads. In practical terms, the project resembles building a modular port breakwater and substation platform, then towing it offshore and assembling it in open water.

The 23 concrete structures are the physical backbone of the island. Each unit has to be fabricated, cured, sealed, and floated with precision. A small error in weight distribution or structural integrity can turn a tow into a recovery operation.

Jan De Nul said all 23 structures are now complete, meaning the onshore production program has cleared a major risk point: the ability to deliver every unit on time and in workable condition.

With fabrication completed at Vlissingen, the focus shifts to finishing works at the Scaldia terminal.

That handoff matters for logistics planners because it marks a transition from heavy civil production to a more schedule sensitive phase: inspections, outfitting, and readiness for offshore placement.

Anyone who has worked around concrete caisson projects knows the feeling: once the units leave the yard, there is no easy redo. The terminal phase becomes the last realistic window to address defects, ensure tolerances, and prepare for sea fastenings and offshore installation.

Jan De Nul said offshore installation of the remaining structures will resume in spring in the North Sea, alongside continued works to prepare the island’s interior.

The island will sit about 45 km off the Belgian coast and is intended to connect offshore wind farms. While the update does not include new dates or tonnage figures, the spring restart signals that the project is moving into its highest visibility phase, where weather windows, marine spreads, and port readiness have to line up.

For operators and forwarders, it is the kind of schedule that behaves like a ferry timetable: miss the window, and the next one may not come for weeks.

Jan De Nul noted the works are being carried out on behalf of Elia Group, in collaboration with DEME Group.

The combination places two of Europe’s best known offshore contractors on one of the continent’s most closely watched grid connection projects. With offshore wind buildouts accelerating and connection capacity becoming a bottleneck, the Princess Elisabeth Island concept is being tracked well beyond Belgium.

In other words: it is not just concrete in the water. It is a test of whether energy islands can scale grid infrastructure fast enough to keep up with turbines already ordered and financed.