Transportation and installation of two offshore substations Mermaid & Seastar

Market: Renewables and Environmental
Scope of Work: Transportation and installation of two offshore substations Mermaid & Seastar
Location: North Sea, Belgium
Client: Deme Offshore NV
Period: March 2020
HLV: Gulliver

Otary RS NV, Electrabel and Eneco are developing the offshore wind farms Mermaid and Seastar, collectively known as the Seamade project. The Mermaid and Seastar fields are respectively the northernmost and central concessions of the Belgian offshore energy zone. Both offshore wind farms combined have a total capacity of 487 MW, spread over 58 wind turbine generators and will provide 485000 families with green energy. On behalf of DEME Offshore, Scaldis was responsible for the transport and installation of the Mermaid & Seastar Offshore substations.

Scaldis Scope

Efficiency driven transportation concept
Having installed six offshore substations in the Belgian North Sea, Scaldis came up with a new transportation concept for sister substations Mermaid and Seastar. Tailor made and in-house designed seafastening grillages on aft deck of Gulliver partly supported and secured the 1200 ton structures during transit to the field. This innovative method avoided the endeavor of offshore lifting from a barge and the need of auxiliary tugs. Already from the start, there was an intense cooperation with the client. On Scaldis’ request, padeyes were transformed to trunnions to smoothen the process of rigging connection and more importantly the offshore disconnection. The combination of trunnions and soft slings, which are easier to handle than steel slings, even reduced the connection of the rigging to roughly 10 mins.

Swift installation — twice!
On 2nd March 2020, Mermaid offshore substation arrived in Vlissingen where it was picked up by Gulliver. In the evening, Gulliver left the port at high water and sailed towards the field. The crew conducted the DP trials before entering the field and was ready for installation before noon. In front of the foundation, the substation was lifted from deck and Gulliver slowly approached the last 100 m towards monopile in DP2 mode. On the instructions of the heavy lift supervisor, the substation was lowered gently over its stabbing guides. Mermaid was installed in a record time. However, the record stood only 11 days, as we successfully installed Seastar’s substation on 16th March. The team used the period between both installations to finetune the process and this resulted in a flawless operation.

Thanks to a different approach, early involvement and a motivated onshore and offshore team the double scope was a great a succes.