Jan De Nul Launches William Thomson: The World’s Largest Cable-Laying Vessel

Jan De Nul has launched the William Thomson, the world’s largest cable-laying vessel, featuring a record-breaking 28,000-tonne capacity and the ability to operate at depths of 4,000 meters. This ultra-low emission, methanol-ready powerhouse will debut on TenneT’s 2GW program, installing over 2,800 kilometers of subsea cables to revolutionize European offshore wind connectivity.

Belgium | April 7, 2026 – In a major leap for the global energy transition, maritime leader Jan De Nul has officially launched the William Thomson, the second of two record-breaking subsea cable-laying vessels (CLVs). Along with her sister vessel, the Fleeming Jenkin, these ships now stand as the largest and most advanced of their kind in the world, specifically engineered to meet the soaring demand for offshore renewable energy infrastructure.

The scale of these vessels is unprecedented. At 215 meters in length and boasting a staggering cargo capacity of 28,000 tonnes, they offer double the loading capacity of any other cable-layer currently on the market. This massive volume allows Jan De Nul to transport longer continuous cable segments, significantly reducing the number of subsea joints required, a critical factor in enhancing cable integrity and lowering project costs.

Ultra-Deep Capabilities: Reaching 4,000 Meters

The William Thomson is not just about size; it is built for extreme environments. While many vessels are limited to continental shelf depths, Jan De Nul’s new class can operate in ultra-deep waters down to 4,000 meters.

• Tension Power: The vessel features advanced tensioners capable of handling up to 150 tonnes, roughly the weight of the Statue of Liberty, allowing for the safe deployment of heavy high-voltage cables.
• Dual-Depth Layout: A specialized aft-deck setup includes a chute for shallow-water work and a massive cable-laying wheel designed for high-efficiency deep-sea installation.
• Simultaneous Operations: Equipped with three carousels (two on deck, one below) and a dedicated fiber optic hold, the vessel can lay up to four cables simultaneously, maximizing operational windows.

A 2,800-Kilometer Debut: The TenneT 2GW Program

The first mission for this new fleet is nothing short of monumental. The Fleeming Jenkin and William Thomson have been contracted for TenneT’s 2GW program, a next-generation grid connection initiative in the Netherlands and Germany.

The vessels will install over 2,800 kilometers of 525 kV DC cables. These connections will each transport two gigawatts of power, more than double the capacity of current 700–900 MW connections and significantly more than a standard nuclear power plant. Following this, in 2028, the fleet will move to Belgium to connect the Princess Elisabeth Island, the world’s first artificial energy island.

The “Ultra-Low Emission” Standard

In line with the green energy they facilitate, these vessels are classified as Ultra-Low Emission vessels (ULEv). Jan De Nul has integrated a dual exhaust filter system that removes 99% of nanoparticles, meeting the rigorous Euro VI emission limits.

• Fuel Flexibility: The engines are designed to run on biofuel and green methanol, drastically slashing carbon footprints.
• Hybrid Power: A 2.5 MWh battery pack allows for “peak shaving” and load smoothing, ensuring the engines run at optimal efficiency and providing a spinning reserve during critical operations.

Strategic Expansion: Five More on the Way

The launch of the William Thomson (scheduled for operation in H1 2027) is part of a broader fleet expansion. Jan De Nul is currently readying five additional vessels to bolster its subsea division:

1. Two Cable-Laying Vessels (Fleeming Jenkin and William Thomson)
2. Two Trenching Support Vessels (for burying and protecting the cables)
3. One Rock Installation Vessel (for specialized seabed protection)

“Reliable, affordable and renewable energy, independent of geopolitical tensions, is one of the most important societal challenges of our time,” said Wouter Vermeersch, Director of Subsea Cables at Jan De Nul. “With this wave of investment, we are strengthening our capacity to help build solutions.”

Technical Specifications at a Glance

About Jan De Nul Group

Jan De Nul Group is a global leader in maritime infrastructure, energy, and environmental engineering. A family-owned Belgian powerhouse with roots dating back to 1849, the Group has evolved from a local construction firm into a premier “total solution” provider for the most complex offshore and civil engineering challenges of the 21st century.

The Group operates through four specialized pillars:

• Offshore Energy: A pioneer in the energy transition, Jan De Nul provides turnkey services for the offshore wind, oil, gas, and renewable sectors. Its fleet includes the world’s most advanced jack-up installation vessels and cable-layers, such as the record-breaking William Thomson and Fleeming Jenkin.
• Dredging & Maritime: One of the world’s “Big Four” dredging companies, the Group maintains global trade routes and builds the ports of the future. Recent milestones include multi-year maintenance contracts in Iceland and major reclamation projects in Brazil and Taiwan.
• Civil Construction: From the Oosterweel link in Antwerp to the revolutionary Princess Elisabeth Island, the world’s first artificial energy island, Jan De Nul’s civil wing manages massive infrastructure projects that redefine mobility and energy security.
• Planet Redevelopment: Focused on circularity, this division specializes in large-scale soil remediation, brownfield redevelopment, and environmental dredging, utilizing in-house “biopile” technology to restore contaminated industrial sites.

Innovation & Sustainability

Jan De Nul is recognized for its “Ultra-Low Emission vessel” (ULEv) standard. The Group’s internal design office, one of the largest in the industry, ensures that its newbuilds are future-proofed with hybrid technology and dual-fuel engines capable of running on green methanol and biofuels. With a workforce of “Can-Do” professionals and a focus on Nature-Based Solutions, Jan De Nul Group continues to shape the future of land and water for the next generation.

Source: Jan De Nul