Specialist Fleet Lays Ireland France Interconnector Cable | Season 6 – Episode 34
Floats Apr 10, 2026
In the Celtic Sea, a fleet of specialist vessels is bringing the Celtic Interconnector to completion, comprising 500 km of subsea cable that will connect the power systems of Ireland and France. The cable laying vessel Calypso leads offshore operations, equipped with high capacity turntables, dynamic positioning and tension control systems to install the subsea cable. She is supported by a number of other specialist vessels, including Aethra, carrying out boulder clearance and trenching, while Athena undertakes cable burial using jetting systems. Seapiper installs subsea rock protection along selected sections of the route. A number of guard vessels, including GV Resolution, operate as “guardian angels” throughout the works.
THE INTERCONNECTOR
The Celtic Interconnector, costing €530.7 million and delivered by EirGrid and Réseau de Transport d’Électricité, is a 700 MW HVDC (High-Voltage Direct Current) link that will enable the exchange of electricity between Ireland and France. With the capacity to supply up to 450,000 homes, it represents a key step in the development of a more integrated European energy system.
Extending from Claycastle Beach in Youghal, County Cork to Cléder on the north-west coast of Brittany, the interconnector will form Ireland’s first direct electricity connection to continental Europe. The project represents a significant step in the country’s transition to a low carbon energy future, while enhancing the security of its electricity supply.
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THE CABLES
The underground and subsea cables are being supplied by the French company Nexans, the world’s second largest cable manufacturer. Production is split across its European facilities, with 1,000 km of subsea cable manufactured in Halden, Norway and 180 km of underground cable produced in Charleroi, Belgium. Accessories are made in Cortaillod, Switzerland, while the 400 kV HVAC 10 km grid connection in Ireland also forms part of the Nexans contract.
THE VESSELS
Since work began in August 2025, the project has progressed in stages, with specialist vessels carrying out surveying, route clearance, cable laying and protection.
THE CALYPSO
Launched in 2023 the Calypso is a purpose-built cable laying vessel and the primary ship deployed on the Celtic Interconnector project, she began installing the 500 km HVDC (High-Voltage Direct Current) cable in August 2025, completing the first 84 km of cable laying before September 2025. Measuring 131 metres in length, she is owned by the Dutch family company Van Oord. Designed for high-capacity cable operations, Calypso is equipped with two 4,000-tonne carousels, one mounted on deck and a second below decks, providing a combined capacity of 8,000 tonnes.
Other vessels involved in site preparation and cable protection include:
THE AETHRA
Callsign SVDM6, she is a DP-2 trenching support vessel designed for global subsea operations, supporting trenching vehicles as well as cable laying, repairs, diving, ROV, survey and IMR work. She is equipped with a moonpool, ROV hangar for two WROVs, a 100-tonne A-frame, and a 150-tonne offshore crane with heave compensation and a 15-tonne auxiliary hoist. On the Celtic Interconnector, the Aethra carried out pre-trenching, boulder clearance and cable burial operations between Wednesday 21 August and Tuesday 1 October 2024.
THE ATHENA
Call sign SVDO4, she is a DP-3 trenching support vessel of MarinTeknikk MT6024 design, equipped for cable laying and repair, as well as diving, ROV, survey and IMR operations. She features a twin-deck arrangement, a 150-tonne AHC A&R winch, a 275-tonne offshore and subsea crane, anchor handling and towing winches, integrated saturation and surface diving systems, and a helideck. On the Celtic Interconnector, Athena is carrying out post-lay burial cable protection, including jetting and trenching from 10 August 2025, with this phase expected to last approximately 135 days, subject to operational and weather conditions.
THE SEAPIPER
Operated by the Dutch company Boskalis, she is a subsea rock installation vessel responsible for seabed protection along the cable route. Measuring 147.24 metres in length with a 36-metre beam, she is equipped with a DP2 positioning system and can install rock at rates of up to 2,000 tonnes per hour to depths of 500 metres using a fallpipe system. An inclined fallpipe, adjustable between 23 and over 50 metres, allows precise placement to depths of around 70 metres.
GV RESOLUTION
A number of guard vessels, typically converted fishing boats or small offshore support craft, operate alongside the cable-laying fleet. Painted in a distinctive black and yellow colour, boats like the GV Resolution (PD.797), photographed in Kilkeel Harbour, County Down by Ireland Made contributor Ernie Patterson, act as “guardian angels” during operations. They provide 24-hour monitoring and maintain a safety exclusion zone around the works, helping to manage risks from passing marine traffic, particularly fishing vessels.
NEARING COMPLETION
According to the Celtic Interconnector Newsletter, as of March 2026, 95% of the HVDC cable has been installed, including 40km underground cabling in Brittany and 35km underground cabling in County Cork. At the Ballyadam converter station, terminations are complete, civil and electrical works are nearing completion, and installation of high voltage equipment and control systems is well advanced. By 2028, final marine installation and burial are to be completed, followed by commissioning, trial operation and entry into commercial service.
EU COUNCIL PRESIDENCY
As Ireland prepares to hold the EU Council Presidency from July to December 2026, focus is increasing on securing our vast maritime area, with an Exclusive Economic Zone over seven times the State’s landmass. Key threats include vulnerable subsea infrastructure such as data cables and the new Celtic Interconnector, activity from Russia’s “shadow fleet” and wider hybrid risks including sabotage, drones and cyberattacks.
In response, the government is strengthening cooperation with EU partners and exploring support from neighbouring states such as Britain and France, while also seeking to address capability gaps in naval vessels and maritime patrol aircraft to better protect our waters.
If you have an idea for a story, please email Kevin Reid [email protected]
Sources of Information, Photo, Video & Music Credits:
All music and sound effects used in Ireland Made – Stories of Irish Transport are royalty free and are fully licensed through Epidemic Sound. Ireland Made – Stories of Irish Transport therefore holds the legal right to use this audio material within its productions under the terms of the Epidemic Sound licensing agreement.
Asso-subsea website
Cable carousel photograph – Maxwell
Echo Live website
Eirgrid website
Nexans website
Seas Source website
Vanoord website
VARD website
