IN Brief:
- OSS Zingst sailed from Schiedam and OSS Darß from Vlissingen.
- The two platforms each carry an approximately 450MW equipment rating within the wider 927MW connection.
- HSI is responsible for engineering, procurement, construction, installation and commissioning of both structures.
The two offshore substations serving Germany’s Gennaker wind farm have sailed from Dutch construction yards for installation in the Baltic Sea, marking a further milestone in transmission system operator 50Hertz’s OST-6-1 offshore connection programme.
On 9 October 2026, OSS Zingst and OSS Darß departed their Dutch fabrication yards under the HSI joint venture, comprising Smulders, HSM Offshore Energy and engineering company Iv. The topside and supporting jacket for OSS Zingst departed from Schiedam, while the corresponding structures for OSS Darß left Vlissingen.
OST-6-1 is intended to connect the 927MW Gennaker offshore wind farm to the 50Hertz transmission system on land. The two substations are each described as having approximately 450MW of capacity. These rounded equipment ratings describe the individual offshore platforms; they are not an arithmetic restatement of the 927MW wind farm or the overall connection rating.
The OST-6-1 connection includes offshore cable systems linking the two substations to the onshore transmission network. Each substation must be integrated with those cable connections as well as the wind farm’s collection system, bringing electrical switching, protection and control functions together across equipment installed at sea and the wider transmission infrastructure.
Gennaker lies in the German Baltic Sea, where electricity generated by offshore wind turbines must be collected and transferred through dedicated high voltage infrastructure before reaching the onshore network. The offshore substations form a major part of that electrical route, accommodating the equipment needed to collect, transform, switch and protect the exported power.
Electricity arrives from the wind farm through its offshore array system. On the platforms, high voltage electrical equipment provides the interface to the export connection. Protection and control systems must detect abnormal conditions and coordinate switching so that faults can be isolated while the infrastructure operates within its permitted electrical limits.
The physical arrangement is particularly demanding because the electrical plant must be installed above the sea on a substantial steel topside. That structure sits on a jacket, which transfers the platform’s weight and environmental loads towards the seabed foundation system. The structure must accommodate equipment access and maintenance as well as the stresses associated with marine conditions.
The Zingst topside measures approximately 48 metres by 33 metres by 17.5 metres and weighed approximately 4,700 tonnes at rollout. The scale illustrates why offshore substation delivery involves heavy fabrication, controlled transport and specialist marine installation rather than conventional building construction.
HSI’s engineering, procurement, construction, installation and commissioning responsibility covers both topsides and their associated jackets. The partners have therefore had to coordinate electrical design with fabrication, systems integration, handling arrangements and the installation sequence rather than deliver isolated equipment packages.
Construction of the Darß topside began in March 2024, with its jacket following in early 2025. Work on the Zingst topside began in May 2024, followed by its jacket in early 2025. Separate fabrication and assembly arrangements at the two Dutch yards allowed the substantial structures to progress towards shipment within the same offshore connection programme.
The departures mark the transition from assembly and yard integration to marine transport. Neither platform is yet installed or connected to its export cables, and both still require offshore electrical works before commissioning can begin.
Offshore installation depends on appropriate vessels, lifting and positioning equipment, suitable weather and the ability to integrate the structures with their final foundations. After the platforms are installed, their electrical equipment must be connected to the associated cable systems and tested under the requirements of the transmission operator.
Commissioning will assess whether the equipment performs as designed, including switching, protection, control and the electrical interfaces needed for export. A completed steel structure cannot transmit generation from the wind farm until the relevant systems are installed, connected and authorised for operation.
The arrival of additional offshore wind capacity in the Baltic Sea increases the importance of completing the network assets that carry electricity ashore. The OST-6-1 connection is designed around the needs of Gennaker, but its delivery programme has separate engineering and commissioning milestones from those of the wind turbines themselves.
The two structures have now left the controlled fabrication environment for offshore installation. The next technically significant evidence will be their successful placement, cable integration and completion of operator acceptance tests. Only after those stages can OST-6-1 perform its intended transmission role between Gennaker and the onshore 50Hertz system.
