The steel tube arrived at the site lying on its side, like a fallen smokestack.
It was 275 feet long and 35 feet wide.
A crane on a jack up vessel lifted it upright over the North Sea and began driving it into the seabed.
When the hammer stopped, the first foundation of a 1,400 MW wind farm was in the ground.
How does a vessel handle a foundation tube that wide?
Why 35 feet is so far beyond what the old vessels could handle
For most of offshore wind’s first two decades, monopiles were far narrower than this, commonly well under 30 feet across. That width was less a design preference than a ceiling set by the cranes, gripper frames and hydraulic hammers that jack up installation vessels were built to carry. Push past it and the vessel either cannot take the load or cannot hold the pile steady enough to drive it true.
The turbines changed first. Modern 14 to 15 MW machines stand taller and sweep far more air, and the steel beneath them has grown to match. The result at this site is a foundation up to 35 feet in diameter, wider than a two lane road. Every other number in the project flows from that single dimension.
So the installation contractor built the vessel up to the job. Seaway7 fitted the jack up vessel Seaway Ventus with a custom built mission equipment spread of grippers, pile guides and handling frames designed, fabricated and installed in under two years to meet the project schedule.
What 275 feet of steel looks like before it hits the water
This first driven pile is one of 95 monopiles made for the 1,400 MW wind farm, and the order was split between two fabricators. JVNW is fabricating 45 of the 95 foundations, with the remaining 50 manufactured by Haizea. Each runs between roughly 220 and 280 feet in length, up to 35 feet in diameter, and weighs between 1,200 and 1,800 metric tons. That range alone signals how much the seabed conditions vary across the site.
At the top of that range, the weight alone is roughly that of 900 mid size pickup trucks. The developers describe the record pile, at 275 feet tall and 35 feet wide, as the largest installed to date from a jack up vessel in Europe.
The first of the 95 transition pieces has also been installed. Each collar stands about 66 feet tall, measures 26 feet across and weighs more than 400 metric tons. It sits on top of the monopile and accepts the tower base, lowered into a precise position above a tube already driven into the seabed.
The vessel and the two years it took to get ready
Two years is a compressed timeline for hardware of this scale, where a single gripper frame must hold a steel column plumb through wind and wave while a hydraulic hammer drives it home. Seaway7 is installing all of the East Anglia THREE monopiles and transition pieces, and the same contract, signed in June 2023, also covers seabed preparation, scour protection and the inter array cables.
“This achievement comes after two years of preparation, resulting in Seaway Ventus installing the largest monopile from a jack-up vessel in Europe,” the contractor’s vice president for the UK, Ireland and Asia said when the first foundation went in.
Each pile reaches the site by sea, is upended using the vessel’s crane, slid into a pile guide and driven with a hydraulic impact hammer until the tip reaches its designed bearing depth. The logistical picture behind each lift is almost as striking as the lift itself.
95 foundations spread across a site 43 miles offshore
The 95 monopiles support 95 turbines rated at 14.7 MW each, for a total of 1,400 MW of clean energy and enough to power the equivalent of more than 1.3 million homes. That nameplate figure is comparable to a single large nuclear reactor unit, though a wind farm delivers it only when the wind blows.
The whole project carries a price tag of £4 billion, roughly $5.3 billion, making it one of the world’s largest offshore wind farms. Every foundation sits approximately 43 miles from the Suffolk coast, spread across 95 positions. Spread that cost across those 95 positions and a single north sea monopile still represents a serious slice of the investment.
A comparable effort shows how closely foundation dimensions must match the site and the ship. One vessel handled a full foundation campaign at Denmark’s largest offshore wind farm, a reminder that the vessel to pile match matters as much as the turbine spec. And separately, the export infrastructure that ties a wind farm to the grid carries its own engineering record: an export cable running 105 miles from a wind farm to Long Island carries current that never changes direction the way every other line in the country does.
What comes after the first pile and what it means for the next generation
That first lift is no longer alone. All 95 foundations are now installed off the Suffolk coast, all 95 transition pieces are complete, and turbine installation has crossed the halfway mark. The wind farm is scheduled to become fully operational by the end of 2026.
Verticality is where the money goes. A single degree of error at the pile becomes several feet of misalignment 500 feet up, so the gripper frames and pile guides earn their cost on every lift. One wrong hammer blow compounds all the way to the nacelle.
The 35 foot diameter that set this record is already shaping how the next wave of installation vessels gets designed. Every dimension in a modern offshore turbine is larger than the one it replaced, and every piece of equipment that touches it has to grow to match. The custom engineering behind this campaign is the proof that the vessel problem is solvable, one hammer blow at a time.
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