Mammoet has deployed its PTC 210 DS ring crane in Scotland to lift 114 wind turbine foundation jackets on a facility set to power two thirds of Scotland’s population.
Completing the work for Global Energy Group at the Port of Nigg to construct the marshalling facility for the Seagreen Offshore Wind Farm, Mammoet proposed the unconventional approach of using its ring crane in tandem with a combination of SPMTs to load out the 2,200-tonne jackets to combat the tidal changes taking place.
The eventual process Mammoet proceeded with took years to formulate, as they sought to factor in water level changes of more than four metres every six hours. Using a conventional approach of a fleet of just SPMTs would not do as the tides would result in the machines becoming redundant, associated costs would blow out thanks to the downtime experience by the SPMTs and the installation vessel in the water.
Mammoet’s solution included the use of a ring crane, as the machine would no longer experience operational time frames thanks to the crane being located on a barge deck and thus no longer needing to remain level with the quay, with UK Technical Sales Manager Oliver Smith saying it was “not at all” a simple process to come by.
“When an organisation is deciding on a project of this scale, cost-efficiency is always an important factor,” he said. “We were involved with this project years in advance – well before some of the full details came to light. It was only further down the line that we needed to reassess the situation and move away from SPMT-only operations.”
Even if tidal conditions are good, it still requires one shift to load each jacket using SPMTs, according to Mammoet. The other advantage of using the PTC 210 DS is that it is capable of loading-out two jackets in a single shift, providing barges are ready for it. This accelerates the pace of work significantly, increasing the feeder vessel cycle time and reducing downtime for the installation vessel at sea.
Furthermore, with the ring crane in operation loading the jackets out onto the installation vessel, Mammoet could use its SPMTs to offload others into the crane’s vicinity, ensuring a smooth, parallel process was performed.
“We knew this method was safe, flexible and more cost-effective than using SPMTs,” said Smith. “Now we can share it with the wider industry so it can serve as a template for how to get offshore wind infrastructure in the water faster and more cost-efficiently; especially where tidal variances are high.”
Seagreen will be the world’s deepest fixed bottom offshore wind farm, lying further from the coast where winds are stronger and more reliable. As a result, its 114 wind turbine foundation jackets stand 95m tall, and are robust enough to support new 10MW variants of Vestas turbine.
Watch the video of the engineering feat here.