Demands placed on cable kit growing as offshore wind market evolves

Designing and installing ever-greater cable capacity on a vessel has become increasingly challenging, whether a vessel is a newbuild and designed from the outset with maximum cable-carrying capacity or a conversion.

In both cases, there are limits to vessel size and deck space, and to the height of the basket on a carousel. As baskets get higher and higher, so the compression forces on a cable at the bottom of the basket grow, and as the weight of cable and height of the basket grow, so vessel stability becomes more of a challenge.

Like other cable vessels, an inter-array cable vessel needs to be able to carry the maximum amount of cable possible. But laying inter-array cables is an intricate job and a ship’s dimensions should not prevent it from efficiently operating in an offshore windfarm.

“In ideal circumstances, when laying cable, a vessel would be manoeuvred so that it is facing into the prevailing wind, but the orientation in which the array cables in an offshore windfarm need to be installed may make that impossible,” Mr Rippe tells OWJ. Hence the need to ensure that a vessel’s dimensions are kept within bounds.

DEME’s dynamic position class 3 cable installation vessel Living Stone entered service in 2018 and in 2020 was awarded a contract to install the inter-array cables for the massive Dogger Bank project in the North Sea. It was selected based on the vessel’s cable capacity – more than 10,000 tonnes. But as Mr Rippe notes, at 147 m in length, it is a large vessel compared even to other recently introduced inter-array cable vessels.

Compared to Subsea 7’s inter-array cable vessel Siem Aimery, which is 95.3 m in length with a cable capacity of 2,500 tonnes, it is a very much larger vessel, but Subsea 7 will soon have available another inter-array and export cable vessel in the form of 130-m Seaway Phoenix (the former Seven Phoenix), which is currently being converted. It is due to enter into operation in Q2 2021.

“There are a lot of very capable oil and gas vessels for which there isn’t enough work at the moment,” says Mr Rippe. “Cable lay may not give owners the margins they are used to employing vessels on the kind of work for which they were originally designed, but several owners are looking at the cable-lay market for employment.

“With contracts for work in two to three years’ time, they are looking at vessels that are currently in warm stack or cold stack and their potential to be converted. They can see a growing pipeline of offshore wind projects, even though there is currently more capability than demand.

“In favour of converting a vessel for use in the cable-lay market is that a conversion could be available in 12 to 18 months, compared to three years for a newbuild,” says Mr Rippe. “Vessels can be bought for good prices too, because of the depressed state of the offshore oil and gas market.

“But against a conversion is that it involves a certain amount of compromise. MAATS is good at helping clients to minimise compromise and find a cable-lay solution that works, but there are other considerations.

“There is also an ever-greater emphasis in the industry on the environmental credentials of a vessel and on new types of more environmentally friendly propulsion solutions.

“The right type of vessel can be upgraded – with batteries, for instance – but there is only so much you can do with a vessel that is 5-10 years old. More and more often when a tender is being assessed, a green vessel with an advanced propulsion system will win points that a converted vessel simply cannot.”

Subsea 7 estimates it will cost approximately US$25M to convert Seven Phoenix to a cable-lay vessel. In a recent investor presentation, it noted that the vessel has a hull suited to cable lay, that it is being fitted with a new cable-lay system and other equipment on board will also be modernised.

The company says it will be a relatively low cost and fast conversion, giving the vessel a further 15-year design life. Although it has yet to return to service, it is already fully booked in H2 2021 and 2022 and will complement the capability of Subea 7’s Seaway Aimery.

Further orders for newbuilds and conversions are on the cards, but for vessel owners, the calculation they make about whether to order a new vessel or to convert one to meet expected demand is not just about the supply and demand equation.

“For a growing number of companies, it’s not just a straightforward calculation about how much demand there might be two to three years or four to five years from now,” Mr Ripper concludes.

“It’s about maintaining market share. It’s part of a strategy they have adopted for the renewables market of being able to offer heavy-lift installation services and cable-lay.

“It’s about being able to provide a whole-of-field approach and offer a full range of services needed to install an offshore windfarm in its entirety.”

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