Our experience for your success

OWP Arkona – Interim Works and Services

On contract with the AWE-Arkona-Windpark Entwicklungs GmbH (a joint venture between E.ON Climate & Renewables and Statoil), OIS took over the maintenance and service activities during the construction phase up to commissioning for the Arkona Baltic Sea offshore wind farm.  The "Interim Works and Services" contract was handled in and from Sassnitz-Mukran off the island of Rügen.

The scope of work consisted of mechanical and electrical maintenance and repair work as well as the preparation work for offshore assembly.

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The focus was on the preparation of all offshore structures, particularly the monopiles and transition pieces (TPs) for wind turbine assembly. The work and services included:

  • Preparation of the TPs onshore for bolting taking place offshore.
  • Inspection of the condition of the flanges and measurement with the designated system
  • Maintenance of electrical components and measurement of electrical connections
  • Inspection of HSSE equipment and assistance with recertification, as required
  • Mechanical and electrical repairs of offshore structures
  • Bolting of tower segments onshore
  • Replacement and maintenance work during the interim phase at sea.

OIS started service work in October 2017, initially onshore. Among the highlights of the project, was the preparation of the tower segments for offshore installation, which also took place in Sassnitz-Mukran, while in parallel 6 technicians also prepared the installations offshore in a 14-day rotation. From December 2017, 9 service technicians were then deployed offshore at 14/14 intervals until mid-2018.

An additional event was the ceremonial inauguration in April 2019, including the then-German Chancellor Angela Merkel and the Prime Minister of Mecklenburg-Western Pomerania, Ms. Schwesig.

The contract came to sucessful completion with the start of operations in July 2019.

Several media reported on the Arkona offshore wind farm:

Ostsee-Windpark Arkona geht in Betrieb : Zeitung für kommunale Wirtschaft (

Offshore-Windpark Arkona | Betriebsstandort von RWE

OIS GmbH erhält Offshore-Auftrag in der Ostsee - OIS (

OSS NSO, Amrumbank, Arkona Service & Maintenance of the Auxiliary Systems

In 2021, OIS Offshore Industrie Service GmbH was contracted by RWE Renewables GmbH in Hamburg with the maintenance and service for the substations Nordsee Ost and Amrumbank in the North Sea and Arkona in the Baltic Sea. The contract period is 3 years.

The contracted services mainly consist of the maintenance and servicing of the following systems:

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  • Oil separator,
  • fuel system,
  • air conditioning and ventilation system,
  • cranes,
  • fire alarm and fire extinguishing system as well as
  • fire extinguishers and fire doors

Additionally, general inspection of the condition of the corrosion protection with a FROSIO inspector and cleaning work, e.g. of the top and helideck, are also part of the OIS responsibilities.

In addition to OIS' own personnel, specialists from reliable partners and subcontractors are employed, e.g. from the companies Noske -Kaeser Germany GmbH, Emdion GmbH, or PALFINGER MARINE EUROPE B.V.

Following the completion of the commissioning of the Kaskasi offshore wind farm in the North Sea, OIS will also provide the services described on the associated substation.

OWP Baltic 1 – Replacement of hydraulic and gearbox hoses

At the Baltic 1 wind farm, OIS service technicians replaced the hydraulic and gearbox hoses in the turbine generator and the hydraulic hoses of the turbine generator crane on 19 wind turbines.

The operation began in the summer of 2021 with Rostock as the starting port and was continued after the winter break in the spring of 2022 with departure from Barhöft.

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The necessary adjustments to the control system for this work, such as turning the turbine or pitching the rotor blades, were carried out by OIS personnel. In total, up to 6 technicians were deployed per offshore turn.

The hydraulic and gearbox hoses are routinely replaced after the period of use specified by the manufacturer. In the process, up to 67 hoses per WTG were replaced, some of which were only accessible after other parts of the turbine had been dismantled.

Thanks to the reliable maintenance of all companies involved and their staff, the wind farm has been able to reliably supply over 50,000 households with electricity for more than 10 years.

Maintenance of the Dolwin 3 grid connection system

Since 2018, OIS Offshore Industrie Service GmbH and Berlin-based Green Wind Offshore GmbH have been jointly performing maintenance and servicing for the DolWin3 grid connection system. This system is used to connect three offshore wind farms in the North Sea to the onshore station 120 kilometers away. For the contract, the two companies have joined forces in the joint venture "ARGE O&M Projekt DolWin3". The client is General Electric Grid GmbH. The contract has a term of five years.

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The contract consists of a preparatory phase lasting several months and the subsequent five-year maintenance phase and includes maintenance activities both at the DolWin gamma converter station and at the Dörpen West onshore substation.

The consortium is responsible for the complete planning, organization and execution of maintenance on the basis of a specially developed maintenance concept.

In addition to the maintenance and repair work, the operation of a control room, which monitors the entire plant operation and status, and provides an overview of all deployment teams and their activities, is an essential part of the contract. In additionally, a storage, logistics and deployment base will be used in Bockhorn (East Frisia), located close to the onshore substation and the offshore transport base. The creation of these personnel and technical requirements ensures the best possible maintenance process.

Maintenance Process.

Every month, OIS technicians perform the required maintenance and servicing work at the Dörpen West substation and on the OSS DolWin gamma.

A cornerstone of the monthly operations is the controlled disconnection of the grid connection system, which takes place once a year. During this service shutdown, maintenance work is also carried out in areas that are not accessible during normal operation, e.g. the high-voltage rooms. During this shutdown phase, the personnel effort increases from 8-10 service technicians per month to approx. 50-60 technicians.

With the implementation of this concept of performance and condition-oriented maintenance a new service quality in the offshore wind sector will be achieved, which includes considerable optimization and cost-saving potentials.


OIS Offshore Industrie Service GmbH and Green Wind Offshore GmbH take over maintenance for grid connection system DolWin3 -