Heerema Unlocking Baltic Sea with Thialf Crane Modifications

Heerema Marine Contractors is modifying cranes onboard Thialf to enable this world’s second-largest semi-submersible crane vessel to enter the Baltic Sea and work on the Arcadis Ost I offshore wind farm.

Heerema Fabrication Group is fabricating the structures needed for the modification of Thialf’s cranes capable of lifting 14,200 metric tons. Thialf is second in size only to Heerema’s Sleipnir.

In 2022, Heerema will be installing 27 Vestas 9.5 MW wind turbines for Parkwind’s Arcadis Ost I wind farm in the Baltic Sea using the company’s novel Rotor Nacelle Assembly (RNA) installation method. Thialf will be deployed to execute this project.

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However, between Heerema’s home base in the Port of Rotterdam, the Netherlands and the Arcadis Ost project location sits Denmark’s Storebaelt Bridge, also known as the Swan.

The Swan connects the Danish islands of Zealand and Funen and has a clearance of 65 metres, while the distance from Thialf’s floaters to the top of the vessel’s A-frames is 105 metres.

Heerema is now working on unlocking the Baltic Sea region to Thialf without compromising the integrity of the vessel’s massive cranes.

At the moment, Thialf is moored in the Port of Rotterdam undergoing an A-frame modification. This action is possible as Thialf’s A-frames already have hingable corners that can accommodate the NOV custom-designed semi-permanent adjustment system, Heerema said.

Using this system, Heerema can lower Thialf’s cranes and fold the A-frames to create a sufficient air gap when combined with ballasting between the vessel and the Storebaelt Bridge.

An artist’s impression of Thialf going under the Storebaelt bridge. Source: Heerema Marine Contractors

Heerema Fabrication Group’s Opole Yard completed most of the fabrication work. The team fabricated around 150 metric tons of structures required for the modification.

According to Heerema, the Baltic Sea is a unique region for offshore operations with a heterogeneous seabed profile that includes sand, mud, hard clay, and bedrock. This variety of potential seabed materials can make installations challenging, but Thialf’s floating vessel capabilities mean that the company can execute projects no matter what’s below.

”Now that Thialf will be working in the region the lifting capacity has increased by around 10,000 metric tons, so dare to think bigger! We can deliver a range of solutions for offshore wind installation, including wind turbine generators, gravity-based structures, monopiles, pre-piled jackets, and offshore substations, read more about our offshore wind solutions here,” Heerema said.