Approximately 15 kilometres off the coast of Aberdeen, Scotland, Grupo Cobra is working on the Kincardine project, one of the first commercial floating wind farms in the world. Boskalis is involved in the project as a transport and installation contractor. Managing Director Marine Services Steve Van Hulle talks about the ins and outs of the activities.

Floating wind farms are mainly installed in areas where the water is too deep to install turbines on foundations such as monopiles or jackets on the seabed. In the near future, these will be the waters off South Korea and Japan, but also the east coast of the United States, the Mediterranean Sea and the northern North Sea.

In Northwest European waters, fixed wind farms are the most obvious option. In the future, when costs come down, floating wind may be an interesting option. But this is not yet the case. For the time being, floating wind farms are small-scale projects, sometimes even in the form of demonstration projects. It is expected that floating wind will take off after 2025, with wind farms becoming steadily larger.

Floaters ideal for turbine maintenance

A floating wind turbine can be described as an enormous anchored float. They come in the form of a spar, a floater and a tension leg. The anchoring system consists of drag anchors, suction piles or driven piles to which chains, steel wires or polyester lines are attached, which are in turn connected to the floaters.

‘The type of anchoring system depends on the water depth, the size of the floater and the weight. For Kincardine we use drag anchors,’ says Van Hulle. ‘The advantage of floaters is that they can be disconnected relatively easily. That is ideal for the future, to carry out maintenance on the turbines.’

For Kincardine, Boskalis is working with floaters, which are semi-submersible foundations on which the turbines are placed, each connected by three chains 100/150 mm thick at a depth of 50 metres. But since floating wind is still in its infancy, own designs for floaters and anchoring systems are still being experimented with.

‘Of course, we already had expertise in the field of renewables, fixed wind farms and in the area of cable laying. We are bringing that expertise to floating wind. In addition, we have experience with the transport and installation of oil platforms and FPSOs, including pre-mooring installations, towing, positioning and hook-ups,’ says Van Hulle.

This also means that the equipment usually used for transport and installation of oil and gas platforms can also largely be used for floating wind projects.

Arrival of a foundation for Kincardine in Rotterdam (photo: Boskalis).

Multiple transport options available

The transport work that Boskalis carries out within the scope of the Kincardine project can be wet or dry. In the latter case, the company works with a transport barge, which it tows. ‘In Spain we do the roll-on of the foundation onto the barge. Then we transport it to a sinking location in the port of Rotterdam, where we do the float-off. The client then has the turbine installed at great height,’ Van Hulle explains. Alternatively, Boskalis can work with one of its heavy-lift vessels instead of a barge.

After this pre-commissioning, the floater is towed with a heavy sea tug, in this case the Manta, via the deep-water route towards Scotland. ‘This trip takes eight to nine days at an average speed of 3 to 3.5 knots. We cannot sail too fast because of the forces that are exerted on the steel of the turbine.’

Also read: Boskalis tows out first floating turbine for Kincardine

Once at the Kincardine wind farm site, Boskalis has a tugboat at its disposal to bring the floater into position. The company also works with the anchor handling tug Nicobar, which not only serves as a hookup vessel, but also as an accommodation vessel for the team responsible for the installation.

So far, two floating turbines have been successfully installed for Kincardine. Boskalis is scheduled to pick up the third floater in Spain in mid-March and tow it to the site in mid-April. This will be followed by numbers four and five.

‘Normally you don’t do that kind of work in winter, but because of the corona crisis the whole schedule has been shifted. In Spain in particular, they had to deal with a lot of problems and delays due to Covid-19,’ says Van Hulle about the postponed planning.

Kincardine tow-out from Rotterdam to Scotland at open sea (photo: Boskalis).

Prelude to larger commercial floating parks

Kincardine is a special project for Boskalis, not only because it is one of the first commercial floating wind farms, but also because with a nominal capacity of 50 MW it is currently the largest. ‘We want to take advantage of this, because we are very ambitious when it comes to floating wind,’ says Van Hulle.

Also read: VIDEO: Installing the North Sea’s first semi-submersible floating wind turbine

For Boskalis the project is a prelude to and preparation for the larger commercial floating wind farms. In this way, the company wants to increase its knowledge and build up a track record. This will allow Boskalis to implement the lessons learned at the earliest possible stage.

‘In this kind of work, it’s all about efficiency of the various cycles,’ Van Hulle explains. ‘With floating wind, think of the pre-mooring cycle, the hookup cycle, etc. You try to make each part as efficient as possible and to limit the execution risks. This is certainly the case if, in the long run, your scope of work exceeds the transport and installation of the turbines alone. Then you reap the benefits of efficiency in installation.’

Picture (top): Kincardine tow-out from Rotterdam to Scotland (by Boskalis).

This article first appeared in Dutch on Schuttevaer, a publication of SWZ|Maritime’s publishing partner Promedia.