IJmuiden Ver Beta: Inside Europe's Largest Offshore Grid Build and the 1,700-Tonne Jacket Taking Shape at Vlissingen

The short version

At Heerema Fabrication Group's yard in Vlissingen, the Netherlands, the first major structural element of the IJmuiden Ver Beta offshore converter platform jacket has been completed and rolled up — lifted from horizontal fabrication position to vertical using two cranes. The element weighs roughly 1,700 tonnes. First steel was cut in September 2025. The jacket is one of a family of large steel substructures being built for TenneT's Dutch and German North Sea grid connections, a programme that is arguably the largest single driver of European offshore steel demand this decade.

That is the news. What follows is why a single jacket milestone sits inside a much bigger story about how the Netherlands is rebuilding its offshore electricity backbone — and what it means for fabricators, steel suppliers and the wider offshore supply chain.

What is actually being built

TenneT, the Dutch-German transmission system operator, is developing a set of offshore grid connections under the Dutch government's offshore wind road map. IJmuiden Ver is one of the designated wind energy areas off the Dutch North Coast, roughly 60–70 km from the coast, and it is being developed in zones (Alpha, Beta, Gamma).

TenneT's role is not to build the wind farms — that is done by developers such as RWE, Vattenfall and others — but to build the offshore converter platforms that collect the power and transmit it to shore as high-voltage direct current (HVDC). These platforms are among the largest and most complex steel structures ever installed in the North Sea.

The IJmuiden Ver Beta connection is a 2 GW HVDC link. For scale: 2 GW is roughly the output of two large nuclear units, or enough to power around two million Dutch households. It is part of a broader Dutch programme (IJmuiden Ver Alpha, Beta, Gamma, plus Nederwiek and other areas) and a German programme (Baltic and North Sea hubs such as BorWin, DolWin and LanWin) that together are intended to deliver tens of gigawatts of offshore wind capacity by the mid-2030s.

The contract structure: who is doing what

The IJmuiden Ver Beta platforms (there are typically two — an offshore converter platform and an onshore converter station) were awarded to a consortium of GE Vernova and Seatrium. In March 2024, TenneT announced a set of framework agreements worth a combined figure reported in the region of €23 billion covering multiple 2 GW HVDC connections in the Dutch and German North Sea — one of the largest offshore transmission procurement packages ever assembled. The GE Vernova–Seatrium consortium was one of the winning parties.

Within that structure:

This is a common pattern for North Sea converter platform jackets: the EPCI consortium owns the overall platform delivery, but the structural steel — the jacket — is subcontracted to a specialised fabricator with a suitable yard, quay and heavy-lift capability. Heerema Fabrication Group operates one of the few European yards with the combination of deep-water quayside access, lifting capacity and offshore fabrication track record needed for structures of this size.

The jacket, and why it matters

A converter platform jacket is a four-legged steel lattice substructure that stands on the seabed and carries the platform topsides above the sea surface. It is not a wind turbine foundation — it is bigger, heavier and more complex, because it has to carry a converter station, transformers, switchgear and typically accommodation and helideck rather than a single turbine tower.

Two numbers shape the engineering:

• Water depth. IJmuiden Ver sits in the order of 25–35 metres of water. That is moderate by North Sea standards — not the 60–70 m challenges of Norwegian or Faroe-Shetland waters — but still demanding enough that jackets are preferred over monopiles for a structure this heavy.
• Topsides mass. Converter platforms of this class commonly have topsides in the 10,000–15,000 tonne range, which means the jacket must be engineered for substantial vertical and dynamic loading, plus fatigue from waves and wind over a 30–40 year design life.

The 1,700-tonne element that was rolled up is a portion of the jacket — likely a leg section or a lower frame assembly — not the finished structure. Full jackets of this class typically weigh several thousand tonnes and are assembled from many such elements. The roll-up itself is a routine but critical fabrication step: rotating a fabricated assembly from horizontal to vertical so that successive sections can be stacked and welded into the final geometry.

Fabrication timeline

A roughly twelve-month gap between first steel cut and first roll-up is normal for a jacket of this scale: the early months are dominated by plate and tubular procurement, cutting, forming, edge preparation and sub-assembly, before the first large integrated elements come together.

Where the steel goes — and why it is hard to see

The public record on IJmuiden Ver Beta's jacket is thin on steel specifics: no published grade mix, no plate or tubular specification, no named steel suppliers, no contract value. That is typical of offshore substructure fabrication. Structural steel for jackets is usually specified in the S355 / S420 family under EN 10025, with enhanced through-thickness and toughness requirements for primary nodes, and increasingly with specialised grades for fatigue-critical connections. Tubulars are typically seamless or longitudinally welded pipe, with node castings or forged inserts at the critical joints.

What is visible is the demand signal:

• Heerema's Vlissingen operation is one of a small number of European yards competing for this work. That concentration matters — jacket fabrication capacity in Europe is limited, and the same yards are being asked to deliver substructures for Dutch, German, UK, French and Baltic projects simultaneously.
• A single 2 GW converter platform jacket consumes thousands of tonnes of heavy plate and tubulars. Multiply that across the roughly 11 connections in the TenneT 2 GW framework package and you get a structural steel requirement measured in the hundreds of thousands of tonnes.
• That demand lands disproportionately on European plate mills with the necessary certification, thickness capability and delivery reliability — a shortlist that is significantly smaller than the list of mills that can supply ordinary structural steel.

The competitive tension here is real: European fabricators are under pressure from Asian yards on price, while European mills are under pressure from imports on volume. Converter platform jackets sit in a segment where quality and certification requirements still favour European supply for the critical elements, even if secondary steel can be sourced more broadly.

The 1,700-tonne roll-up is a useful reminder that this is not a thin-margin commodity business. It is heavy, precision fabrication on a 30-year asset — and the mills that supply it are effectively partners in a multi-decade offshore transmission programme.

Why this project matters beyond the Netherlands

1. It is a standardisation play. TenneT's 2 GW HVDC platform design is deliberately modular and repeatable across the Dutch and German North Sea. If the consortium can build the same platform type at multiple sites and in multiple yards, the cost curve bends. The IJmuiden Ver Beta jacket is an early test of whether that repeatability actually materialises in the fabrication yard, not just on the drawing board.

2. It de-risks the Dutch 2030 targets. The Netherlands has committed to roughly 21 GW of offshore wind by 2030, with IJmuiden Ver as a centrepiece. That capacity is only as real as the grid connections that carry it to shore. Converter platforms, not wind turbines, are the most common schedule bottleneck in offshore wind programmes across Europe. Progress at Vlissingen is progress on the timeline that matters most.

3. It reinforces the North Sea as a shared industrial system. Dutch platforms, German platforms, UK platforms and Norwegian platforms are being built in overlapping yards by overlapping contractors and supplied by overlapping mills. The IJmuiden Ver Beta jacket is a node in a supply chain that is becoming more integrated — and therefore more exposed to a single yard outage, a single mill's delivery delay or a single certification gap.

What to watch next

• Jacket completion and load-out. The next public milestone is likely to be completion of the full jacket and load-out from Vlissingen, which will indicate the actual fabricated weight of the structure — a useful benchmark for future jacket estimates.
• Installation window. No installation date has been stated publicly. Jacket installation typically requires a heavy-lift vessel, and the North Sea heavy-lift fleet is heavily booked, so the installation slot is often the binding constraint.
• Whether the steel sourcing becomes visible. Contract values and steel suppliers are rarely named, but if TenneT or Heerema publish a mill or a tonnage figure, that would give the first real read on European plate demand from this programme.
• Repeat builds. Whether Heerema is awarded jackets for additional TenneT 2 GW connections will say a lot about whether European fabrication capacity is scaling for the programme or merely absorbing a one-off order.

Bottom line

A 1,700-tonne steel element being rolled up in a Dutch yard is a small event in a large programme. But the IJmuiden Ver Beta jacket is a fair proxy for the state of Europe's offshore grid build: technically demanding, steel-intensive, dependent on a handful of specialist yards and mills, and proceeding steadily rather than spectacularly. For the steel industry, the takeaway is straightforward — the North Sea's transmission build-out is a durable, certification-constrained, high-specification demand pool, and the yards and mills positioned for it are being locked in now, jacket by jacket.