Equipped for safety and comfort, the new generation cable layer Nexans Aurora can handle the heaviest subsea cables efficiently in shallow or deep water
Bristling with new-generation technology to maximise its efficiency and flexibility, Nexans Aurora joins the global cable-laying fleet amid a booming offshore wind market, heading to work within weeks of delivery from Norway’s Ulstein Verft.
A project largely executed by the ‘Norwegian maritime cluster’, the 150 m-long and 31 m-wide vessel is signed for a string of work running long into the future according to owner Nexans. “[It includes] the interconnector between Crete and Attica in Greece, the Seagreen offshore windfarm in Ireland and the offshore Empire windfarm in the US,” the Paris-based cable and optical fibre provider tells OSJ.
Although Nexans did not reveal the cost of its new flagship, OSJ has been advised it was a substantial part of a €360M (US$427M) investment that includes the transformation of the Charleston plant in the US to that country’s first high-voltage subsea cables infrastructure.
The cable layer enters a dynamic market, with offshore wind booming in Europe, the US and UK. Earlier this year the EU announced plans to increase the amount of power it generates through offshore wind by 25 times within less than 30 years. The EU is aiming for 60 GW within a decade, while China and India between them expect to build 80 GW in the same period. The US meantime is committed to adding 20 GW every year, according to the International Energy Agency.
All this energy must be hooked up by vessels like Nexans Aurora and clients are queuing up. The ship’s advanced technology has already attracted some plum contracts, with Nexans being named preferred supplier to help electrify New York State by connecting the Empire offshore windfarms to the grid.
Nexans Aurora was designed for installing HVDC and HVAC cable systems in all weathers by virtue of an ability to stay on station. The vessel is also equally comfortable in deep or shallow water. Finally, high levels of manoeuvrability qualify the cable layer for the dynamic positioning three classification (DP3), the highest awarded by class society DNV.
The Silent-E notation, also awarded by DNV, which has been instrumental in developing guidelines for underwater noise, is another ecological plus. “Our first concern is that our operations do not have a negative impact on the environment, and this extends to underwater radiated noise,” explains Nexans group project manager Frode Beyer, citing specific local requirements that are designed to protect vulnerable surroundings.
The massive on-deck infrastructure has set new standards. Among numerous innovations, the traditional turntable has been redesigned to carry a record amount of cable. The concentric arrangement – “carousel in a carousel” – can handle two cables simultaneously and store up to 10,000 tonnes of a single length and up to 5,000 tonnes in each basket. The result is the world’s largest offshore carousel, according to Mr Beyer.
As UK-based consultant MAATS, designer of the equipment, notes, “[The] system consists of an on-deck, concentric, 10,000-tonne carousel and two separate firing-line deck-spread systems, one line utilising a capstan lay solution while the other adopts the use of two twin-track 25-tonnes tensions, each providing four points of contact to the product.” Complementing the system are a range of heavy-duty roller pathways, two loading arms and stern lay wheels, all of which help enable laying in deep water, harsh conditions and rough weather.
There is also space for a container garage with handling systems and storage positions for nine 20-ft containers arranged in-house. “This enables efficient mobilising and demobilising between missions,” designer Skipsteknisk tells OSJ. It adds: “An automated handling system for up to eight workboats is situated in a protected area on deck.”
The quality of the accommodation has not been neglected either. It was a stipulation of Nexans that the crew be comfortably accommodated. There are 90 single-bunk cabins with plenty of space.
Nexans Aurora was a long time in the planning. “Nexans has been considering this kind of vessel for several years,” explains Mr Beyer. Over the years since Nexans’ workhorse vessel Skagerrak was built in 1976, cables have become longer, larger and heavier. Its replacement can handle cables of more than 400 mm, all of which however place more stress on the rest of the handling equipment, as the loads increase exponentially.
Also, adds Mr Beyer, cables are being laid at ever greater depths. “More cable in the water means more weight,” he says. “This requires additional strength in topside handling gear.”
Another influence on the design of the deck infrastructure is the stipulation by windfarms for handling gear that can bundle two cables together or lay them in parallel. The carousel – or turntable – is a high-capacity split system and is located midship, rather than the usual two single turntables. The benefits, explains Mr Beyer, are “flexibility, saved space and [it] helped keep the ship’s dimensions down.”
“More cable in the water means more weight, requiring additional strength in topside handling gear”
To lay cables through two types of lines, there is a capstan winch for deepwater operations and a standard tensioner line for shallower water. “This is a configuration only possible with a tailor-made cable layer,” he says.
Although the 17,000-tonne vessel’s deepwater capabilities attract most of the interest, its shallow-water operations are equally as important because windfarms are often located close to shore in environmentally sensitive areas. And vitally, Nexans Aurora has to load up on cable from a shallow-water quay in Norway before sailing off on its assignments.
“This means that the same vessel has to meet very different performance demands,” points out Bjørn-Oscar Kløvning, sales manager at designer Skipsteknisk, which had a few headaches in coming up with a ship suitable for all seasons and depths.
The build was something of a triumph for the Norwegian maritime cluster, including Ulstein Verft. While building its first-ever cable layer, Ulstein was also fending off the depredations of Covid and still managed to deliver the vessel on time.
Nexans Aurora is unlikely to be Ulstein’s last DP3. “We hope that Nexans Aurora can serve as a door opener to the cable-laying segment,” says Jose Garcia, deputy managing director at Ulstein International. “The Aurora is one of the projects moving the industry into the next generation of cable-laying vessels.”
Truly, a vessel for a new offshore energy era.
A vessel that can do most anything
Norway’s Skipsteknisk design team had to surmount more than the usual number of challenges for Nexans Aurora, particularly in coping with the enormous loads and sometimes shallow operating waters for such a specialised vessel, weighing in at 17,000 tonnes.
Nexans got the designers and engineers off to a good start with detailed instructions about the vessel’s criteria and modes. “That was a good starting point,” Bjørn-Oscar Kløvning, sales manager at designer Skipsteknisk, tells OSJ.
However, that still left some big strength and weight challenges that required close co-operation with class society DNV. “The vessel is a powerful DP3 cable layer designed with high redundancy,” he explains. “Even if it is a big vessel to our scale, you realise that you need all the space you can get in the enginerooms. It is fitted with two operation centres, enabling the owners to operate and navigate from two fully equipped wheelhouses. One is forward, where you normally have the navigation bridge, and one aft, with an overview of the aft part of the vessel where the cable goes overboard. That is where you operate the vessel during cable laying.”
Asked about the biggest challenge, he explains: “The owner had requirements for a minimum deadweight at a maximum draft because the vessel has to pass through a pretty narrow passage out of their cable factories at Halden, Norway. This took a lot of effort to verify upfront [because] it was a completely new design. We ended up with a vessel that exceeded these requirements.”
On the subject of crew comfort (Nexans Aurora has 90 single-bunk cabins), he describes this as one of the major issues. With most of the cargo weight on deck in the carousel, that was a good starting point for a comfortable motion, especially when loaded up with cable. “When empty and filled up with fuel and freshwater, Skipsteknisk designed in two large anti-rolling tanks to make her ‘softer’,” he says.