Only one chance

Precision is very important in offshore projects.During foundation installation the site survey and everything that has to do with measuring techniques, is crucial.  “You only have one chance”, says surveyor Bert Declerck. “If the pile is in the ground and you start tapping it in, you can still adjust during the first five to ten metres, but after that, it’s too late. Then the pile stands and you cannot take it out or straighten it, it must be right from the very first try."

"Survey is crucial."

The survey team used a combination of different techniques. The depth was determined by a multibeam, which uses a technique based on acoustics. The surveyor sends out sound waves that get reflected on the seabed and are caught again. “We also mapped out the seabed with a side-scan sonar, which produces a sort of photographic scan of the seabed and using magnetometers, that measure the magnetic intensity, we checked for the presence of metal objects.”

Stable surface

In the first phase of Nobelwind, a gravel bed was created for each wind turbine. “We first delivered a gravel bed to an accuracy of 20 centimetres high. Then came the foundations themselves, which we had followed from the manufacturing stage to make sure they were manufactured correctly and that they met all tolerances, for e.g. making sure the bolt holes matched.”

“Once the vessel stood on its feet out of the water, the first pile was placed. We measured where the pile was and checked whether it was standing vertically.” Once the pile was in the right place, a hammer tapped the pile into the ground. Onto that hammer, we attached reflectors, which basically are a kind of mirrors, to allow us to closely monitor the hammer and we used lasers to check that the hammer had not damaged anything.”

The Nobelwind project comprised 50 turbines, all installed within the required tolerances. “This project had a very steep learning curve and all the teams became finely tuned with each other as the techniques were improved and refined throughout the installation process. Another useful set of experiences that we take with us to a next project!”

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