A photo of the SSCV vessel Thialf installing EnbW Hohe See substation jacket

Thialf Installing Jacket Foundations for Dogger Bank A & B Offshore Substations

Heerema Marine Contractors’ semi-submersible crane vessel (SSCV) Thialf has returned from the Baltic Sea and has been deployed on the Dogger Bank A & B offshore wind farms, where the vessel is currently installing jacket foundations for the project’s two offshore substations.

Illustration; SSCV Thialf installing EnbW Hohe See substation jacket; Photo source: EnBW

According to AIS data available online and a recently issued Notice to Mariners for the project, Thialf arrived at the Dogger Bank Wind Farm area on 5 April and will continue working there until approximately 1 May.

The jacket components are being transported to the project site onboard the cargo barges Saipem 44 and Wagenborg 11 towed by tow tugs AHT Fram Prince and AHT Carlo Martello.

Saipem is responsible for the transportation and installation of the Dogger Bank A and B substations, being delivered by Aibel, under a contract the company signed in 2020 with the Dogger Bank Wind Farm joint venture partners.

Heerema Marine Contractors, whose SSCV Thialf is now installing jackets for the substations of the first two Dogger Bank Wind Farm phases, was awarded the same contract for Dogger Bank C, the third phase of the 3.6 GW offshore wind project.

The 3.6 GW Dogger Bank Wind Farm is being built in three 1.2 GW phases some 130 kilometres off the UK coast.

The project, owned by a joint venture between SSE Renewables (40 per cent), Equinor (40 per cent), and Vårgrønn (20 per cent), will be the world’s largest offshore wind farm once completed, providing enough electricity to power roughly six million UK homes a year.

Offshore construction started last year with the first monopile foundations installed in July 2022 and the first wind turbines are set to be installed soon.

Thialf’s Return from the Baltic Sea

At the beginning of April, Heerema Marine Contractors announced that Thialf, the world’s second-largest semi-submersible crane vessel, made its second passage under the Storebaelt Bridge, also known as the “gate to the Baltic Sea”, on its journey back from the Arcadis Ost 1 offshore wind farm site.

In October last year, the vessel entered the Baltic Sea for the first time ever, on which occasion it first needed to undergo crane alterations to enable reaching a total air draught of just under 65 metres with the A-frames down, while ballasted down to its maximum draught.

This was done as the Danish Storebaelt Bridge has a clearance of 65 metres, while the distance from Thialf’s floaters to the top of its A-frames was 105 metres.

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The vessel was deployed in the Baltic Sea to install the offshore substation at the Baltic Eagle offshore wind farm site under a contract with Iberdrola from May 2021.

Thialf installed the substation’s jacket foundation after arriving in the Baltic Sea last year and lowered the topside at the beginning of this year.

The vessel has also been chartered for wind turbine installation at the nearby Arcadis Ost 1 offshore wind farm, being built by Parkwind, which now has 24 turbines in place, most of them already producing electricity. The remaining three wind turbines are scheduled to be installed later this year due to delays in the deliveries of blades.

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On its return journey from the Baltic Sea, Thialf was towed by the Maersk Supply Service’s tug Maersk Handler.


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