Jan De Nul Launches Second Cable Laying Giant

Jan De Nul has launched William Thomson, the second of two identical subsea cable‑laying vessels currently under construction.

Both vessels have a cargo capacity of 28,000 tonnes and a length of 215 metres. This makes them the largest of their kind, Jan De Nul said.

Jan De Nul’s two new cable-laying vessels have been specially built to install subsea cables, both in shallow and ultra-deep waters down to 4,000 metres. Thanks to their large loading capacity, they can take longer cables on board in a single piece and bridge longer distances with as few subsea cable connections as possible.

Compared to other cable-laying vessels on the market, they therefore also need to make fewer return trips to load cables. This reduces costs, minimises the environmental footprint and enhances cable quality, Jan De Nul said.

William Thomson’s sister vessel, Fleeming Jenkin, was launched in October 2025 and her delivery is scheduled for the last quarter of 2026.

The William Thomson will follow shortly and will be operational in the first half of 2027. Both vessels and the technologies on board have been designed by Jan De Nul’s in-house experts.

Wouter Vermeersch, Director Subsea Cables Offshore Energy at Jan De Nul, said: ”The William Thomson and its identical sister, the Fleeming Jenkin, bring together all the expertise in cable installation that we have built up over the past fifteen years. They are the highest-performing and most efficient cable-laying vessels on the market.”

Once operational, Fleeming Jenkin and William Thomson can immediately get to work on their first assignments.

Their first project is the 2 GW programme by TenneT, the grid operator for the Netherlands and large parts of Germany. This introduces a new generation of grid connections for offshore wind farms, each capable of transporting up to two gigawatts. That is more than double the capacity of current connections, which typically range between 700 and 900 megawatts, making offshore wind energy more efficient and affordable. By way of comparison, an average nuclear power station typically generates between 1 and 1.6 gigawatts.

For this programme, Fleeming Jenkin and William Thomson will install more than 2,800 kilometres of 525 kV DC cables for four different grid connections.

In 2028, Jan De Nul will also deploy one of these new cable-laying vessels to install three AC cables that will connect the Princess Elisabeth Island to shore.

This energy island, which Jan De Nul is building in a joint venture for grid operator Elia, will bundle the cables from Belgium’s second offshore wind zone (Princess Elisabeth Zone) and enable a stronger interconnection between the North Sea countries.

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