Van Oord Shares Experience with Innovative Foundations (Interview)

As promised, we bring you the second part of the interview with Van Oord’s Commercial Manager of Offshore Wind Projects, Theo de Lange.

In this part we have focused on new technological developments, offshore wind projects they worked on and their vessels.

First part: Van Oord: Dredging Companies Venturing into Offshore Wind (Interview)

OW: Earlier this year, you have completed work on Eneco Luchterduinen offshore wind project that features unique foundations where monopile and the transition piece are built as a single component. What challenges did you face during the installation of these foundations?

De Lange: The Eneco Luchterduinen offshore wind project was a very successful project, we delivered it within budget and well within time, actually, four months earlier. In terms of the integrated monopile transition piece, the installation wasn’t so different. The main challenge was to install all the secondary steel components (ladders, boat landings, platforms) offshore and to drive the monopiles directly without any out of tolerances.  With this concept you don’t  have the possibility to compensate for misalignments like you have with a grouted connection during the installation of the transition piece. For this purpose we developed a special gripper on the Aeolus that worked very well.

OW: Do you see these foundations that have integrated transition piece and the monopile better than those that have separated components?

De Lange: I think it’s an option, and it’s cheaper when you can use it. Although, for example at Gemini we used foundations with a flange where we have a bolted connection between the monopile and the transition piece. It’s always a matter of optimizing. When you have shallow water depths and limited weights, we would do it again. It’s a very successful concept.

OW: For the Burbo Bank Extension offshore wind farm job, Van Oord will use its heavy lift vessel Svanen. Would you mind elaborating on the installation strategy used with this vessel?

De Lange: We will have a marshalling harbour in the neighbourhood, could be Liverpool or Barrow, and all the monopiles and transition pieces will be brought on barges or with cargo vessels towards the marshalling port. Then we will plug the monopiles and put them in the water. From there, the monopiles will be towed to Svanen by means of tug boats. The Svanen, which will be at the construction site laying on an anchor spread, will then upend the monopile and pile it.

OW: Why aren’t those monopiles sailed directly on the barges to Svanen?

De Lange: That’s a logistical matter. You want to have a kind of storage in the marshalling port. And in order to do the upending, the pile needs to be in the water, otherwise, you would be damaging the pile in case you do not make arrangements on the barges. That would make the proces more complex and expensive. The feeder system that the Svanen works with has been used already many times and it has proved to be very efficient.

OW: Why was Svanen chosen over Aelous for Burbo Bank Extension and what are the advantages and disadvantages of both vessels?

De Lange: Aeolus is still occupied with a turbine installation at Gemini at that period, but also the water depth is very shallow at Burbo, so it’s easier to work with the Svanen than with the Aeolus. It’s also not possible to jack up at all locations there, due to the soil condition, so the Svanen in floating mode is really the optimal solution there.

OW: So is the Svanen weather dependant as it is a floating vessel?

De Lange: Indeed, it has it’s limitation because you’re installing it in a floating mode and when you’re jacking up then of course you have a stable platform.

OW: For the installation of foundations and turbines at Westermeerwind project Van Oord joined forces with Mammoet. Can you tell us more about this?

De Lange: Westermeerwind project was one of the projects that came along with the acquisition of the assets and staff of Ballast Nedam Offshore at the beginning of this year. The project was a Joint Venture with Mammoet, and with the acquisition of Ballast Nedam Offshore, Van Oord became the Joint Venture partner of Mammoet. During the construction the monopiles were brought to the construction site via barges and upended with a floating crane. Due to shallow water with sheltered conditions we used the smaller equipment.

OffshoreWIND staff; Image: Van Oord