Offshore wind farms rely on subsea cables to transmit electricity between wind turbines, offshore substations, and the onshore grid. But these cables can stretch for tens of kilometers and weigh thousands of tonnes.

How can such enormous cables be carefully laid onto the seabed? The answer lies with a specialized vessel known as the Cable-Laying Vessel (CLV).

A Floating Cable Installation Platform
A CLV is an engineering vessel specifically designed to transport and install subsea cables. Unlike an ordinary cargo ship, it carries specialized equipment for cable storage, handling, tension control, and deployment.
The Cable Carousel, introduced in our previous article, is one common storage system. But when a cable leaves the carousel, it is not simply dropped into the sea.
Modern CLVs may use equipment such as tensioners, capstans, and lay wheels or sheaves to control the cable as it moves through the vessel and into the water. 

Laying a Cable Is More Than Letting It Sink
During installation, the CLV travels slowly along a predetermined cable route while continuously paying out the cable.
One of the most important factors during this process is tension control.
Between the vessel and the seabed, the suspended cable forms a curved profile through the water before reaching the seabed. If vessel speed or cable tension is poorly controlled, excessive tensile or bending loads may be placed on the cable.
Installation teams therefore continuously monitor the vessel's position, cable tension, and laying conditions.
This is also why many modern CLVs are equipped with Dynamic Positioning (DP) systems. Using positioning sensors, thrusters, and computerized controls, DP helps the vessel accurately follow the planned cable route without relying solely on anchors.

What Happens After the Cable Reaches the Seabed?
Reaching the seabed does not necessarily mean the installation is complete.
Depending on project design and seabed conditions, the cable may be laid and buried in a single operation, known as Simultaneous Lay and Burial. Alternatively, it may first be laid on the seabed and buried later using dedicated equipment in a Post-Lay Burial (PLB) operation.
Some cable-laying vessels can therefore work with cable ploughs, ROV-based burial tools, or other specialized subsea equipment.

A Cable-Laying Vessel is much more than a ship carrying a very long cable. It is a mobile engineering platform combining cable storage, deployment, tension control, positioning, and offshore installation capabilities.
The next time, you see a CLV with its enormous carousel and cable-handling equipment, imagine this: an electrical artery connecting an offshore wind farm to the power grid is gradually extending from the vessel all the way to the seabed.


References
 • Guide to an offshore wind farm | An informative resource for offshore wind (Image source)
 • Pure player in sustainable electrification - Nexans
 • Prysmian | Cables, Energy & Telecom Solutions | Prysmian