Posted on October 1, 2025
Thousands of kilometres of cables now lie on the seabed. They transport electricity between countries and continents and connect offshore wind farms to the mainland. They are the umbilical cords of the energy transition. Even the bulk of international data traffic runs via submarine fiber cables. But these subsea cables are vulnerable to damage and – because of their strategic value – a target for sabotage. As an expert player in the offshore energy industry, Jan De Nul focuses strongly on the protection of subsea cables and infrastructure.
New rock installation vessel
For 10 years now, Jan De Nul has been putting its full weight behind the offshore cable industry, including the protection of subsea infrastructure. Today we are expanding our fleet of large rock installation vessels. Next to Joseph Plateau and Simon Stevin, the brand-new George W. Goethals will be the third large rock installation vessel in our fleet with a carrying capacity exceeding 30,000 tonnes.
A rock installation vessel protects cables, pipelines and other subsea structures by installing a rock cover layer. With a remotely operated underwater vehicle at the end of the vertical fall pipe, we can install rocks in sea depths up to 2,000 meters with precision. Thanks to the inclined fall pipe, this vessel can also install rocks against or under permanent structures.
Where the soil conditions allow for it, cables can also be protected by burying them into the seabed. We use a trencher to do this, a robot controlled from the ship’s deck that operates underwater. This robot typically buries the cable by driving over it (post-trenching) whilst simultaneously fluidizing the soil, which allows for the cable to sink through the soil. If the soil is too hard, we will use a trencher that can cut through the seabed. Also, our trailing suction hopper dredgers can tackle a variety of soil conditions. We use these vessels to make a trench ahead of the cable installation but also to clear sand waves.
The energy transition: highly needed, highly challenging
The share of renewable energy is steadily growing in the energy mix. Although the energy transition is a big relief for our environment and a strategic lever for energy security, it does bring its share of new challenges.
First, energy from renewable sources like wind and solar is less predictable and is produced at times and places that do not necessarily match consumer demand. As a result, renewables are seriously putting our current electricity grids to the test. To cope with this problem, energy producers and network operators must work together on new digital technologies and smart, balanced grids.
These grids need to efficiently transmit electricity — produced by a diverse mix of technologies and on different locations — to end users. At the same time, stability and reliability across the system have to be maintained. The offshore infrastructure must also communicate perfectly and integrate with the national electricity grids, each of which has its own grid code and specifications.
Power cables to the rescue
Cables are the perfect way to bring energy generated at sea to land. Similarly, interconnection between countries can only be achieved by the installation of cables, over land and increasingly along the seabed. These high-voltage interconnectors establish the link between energy grids. They are being installed at sea where possible because the permit process for high-voltage overhead lines on land is becoming more and more difficult and onshore buried solutions very expensive.
Cable connections are also needed to cope with the peaks and troughs that are inherent in renewable energy generation. They make it possible to divert surplus production to projects such as hydrodams. The water is pumped up into the dam whenever there is an overproduction of green electricity and flows out again to produce hydro power energy when wind or solar production is lacking. The dam is acting as an electrical energy storage system in this case.
By 2050, all the energy consumed in the Netherlands should come from sustainable sources, such as wind power. Among other projects, the wind farms Hollandse Kust Noord and West Alpha will translate this ambition to reality. They will generate electricity for up to 1.4 million households. Jan De Nul installed 210 kilometers of subsea power cables to bring this energy ashore.
A strategic network that requires protection
Subsea cables are not just technically important; they are highly strategic. As they often lie along routes between economic superpowers, the control or influence over cable networks is taking on a geopolitical dimension. Not only can data traffic come to a halt in the event of damage, but power outages or price increases on energy markets can also result from a disruption affecting a major power connection.
The impact of damage, sabotage or malfunctions is growing now that digital and energy infrastructures are becoming closely interconnected. Protecting this vital subsea infrastructure is therefore a matter of national security, economic stability, and energy security.
Fortunately, more and more measures are being set up to protect submarine cables. For example, there are several international treaties that include rules on the installation and protection of cables. The integrity of cables can be inspected with the help of monitoring technologies. And there are partnerships between countries to implement security and repair measures.
Nevertheless, there is no room for complacency. The dependence on digital networks and green energy means that the consequences of cable breaks are becoming significant. Prevention, security and redundancy are essential to protect this vulnerable network.
