Management Team

Meet our team members!

Our team

All of our senior team members have extensive individual experience in design, engineering and project management in the areas of offshore wind and civil engineering. Our know-how and experience is paired with an excellent individual network in the offshore wind industry.

ONP is managed by our three senior partners each with a long individual track record in offshore wind and major marine infrastructure projects.

The Management

Martin Rahtge

Phone +49 40 3602 527-13
Mobile +49 172 420 8640

Gerd Kroll

Phone +49 40 3602 527-14
Mobile +49 171 492 3973

Stefan Woltering

Phone +49 40 3602 527-11
Mobile +49 160 97272728

Dipl.-Ing. Martin Rahtge is, together with Dr. Stefan Woltering, responsible for the areas of technology and project management.

Following his vocational training in the construction industry, Martin Rahtge studied civil engineering at the Bremen University of Applied Sciences. For three years, from 1981, he worked at Philipp Holzmann AG. Thereafter, he continued his civil engineering studies at the Technical University of Berlin.

From 1988 to 2002, he once again worked for Philipp Holzmann AG, where for the last four years he managed the company's Bremen branch. Thereafter, he joined Hochtief Construction AG, initially as its Bremen branch manager, then as a member of the Hamburg senior management, and finally as its chairman. In this position, Martin Rahtge was responsible for some 450 staff and revenues in excess of 200 million euros per annum.

His vast technical and project management expertise is based on more than 30 years of professional experience, particularly in the area of complex water engineering projects. As early as the 1990s, Martin Rahtge managed large-scale projects involving the construction of sluices, shipyards and port facilities. After the turn of the millennium, he also headed international harbour, bridge and dam engineering projects.

Martin Rahtge developed a particular passion for the field of offshore wind power plant construction, where he, together with his management team, advanced the Offshore business division from its modest beginnings to the market leader of the German offshore wind power industry. Along with his experience in managing large-scale projects, Martin Rahtge also expanded his expertise through the planning, construction and operation of two of the largest and most powerful jack-up vessels in the European market.

In 2014, Martin Rahtge, together with other high-ranking executives from the Offshore business division, launched ONP Management GmbH in order to put his vast knowledge and practical expertise at the disposal of clients engaged in the development, financing and realisation of offshore wind power plants.


Gerd Kroll is responsible for the areas of risk and contract management within ONP Management for project finance.

After completing his business apprenticeship in the construction industry Gerd Kroll studied at the IHK Cologne / Business Institute Düsseldorf to receive his degree as construction business administrator.

Gerd Kroll started his professional career as commercial project manager with the Philip Holzmann AG before he moved to join the HOCHTIEF AG in 1986 where he took over the commercial responsibility for civil engineering and marine works. From 1999 until 2015 Gerd Kroll was a member of the management board of the subsidiary Civil Engineering and Marine Works. He was also Managing Director of the HOCHTIEF Crewing GmbH, which was founded due to his business idea.

His implementing strength is based on thirty years of professional experience, in which the focus was always on project realisation and the build-up and management of business units. He was commercially responsible for the construction of complex marine and civil engineering works such as port facilities, bridges, tunnels and offshore structures.

His main focus in the last years was the build-up of the offshore wind business unit for HOCHTIEF AG. Especially the construction and financing of two large jack-up vessels for the european market is worth pointing out. These vessels have been used in the construction of several Major offshore wind farms.

Together with Dipl.-Ing. Martin Rahtge, Dr.-Ing. Stefan Woltering signs responsible for the areas of technology and project management at ONP Management GmbH.

Following his vocational training as a specialist construction worker for concrete and reinforced concrete structures, Stefan Woltering studied engineering sciences at Hannover's Leibnitz University. Stefan Woltering was already focusing on the subject of marine engineering during his academic studies. Accordingly, he wrote his PhD thesis about the Lagrangian view on the motion of the seastate as part of a coastal engineering project for the German Research Foundation at the Franzius-Institute for Hydraulic, Estuarine and Coastal Engineering, Hanover University.

During his professional career, Stefan Woltering significantly expanded his expertise on both offshore and nearshore projects. For instance, following his doctorate, he worked as a research associate and assistant of the head of the structural engineering department at the port authority in Bremerhaven and later as department manager for port maintenance and port dredging. Moreover, for two years he held the position of divisional head for national traffic affairs at the Bremen senatorial offices of Economy and Ports.

Over the following nine years, Stefan Woltering was instrumental in advancing the international business of Bremenports GmbH & Co. KG, a 100% subsidiary of the Free Hanseatic City of Bremen (former port authority). As sole general manager of this company, he then managed the business of the public infrastructure of the ports of Bremen and Bremerhaven, also with a strong commercial focus.

In 2011, Stefan Woltering moved into the private sector, joining Hochtief Solutions AG, where he initially headed the offshore branch and later on joined the executive committee of the company as a member of the Civil Engineering, Marine and Offshore senior management.

In 2014, Stefan Woltering, together with other high-ranking executives from the offshore division, launched ONP Management GmbH in order to put his vast knowledge and practical expertise at the disposal of clients engaged in the development, financing and realization of offshore wind power plants.