24.06.2026
Since its completion in 1974, the Umlauftank 2 — commonly known as the “rosa Röhre” — on Schleuseninsel in Tiergarten has been a landmark of West Berlin. The technical principle of the ship-engineering test facility, conceived by Christian Boës, consists in immersing a fixed floating body, for measurement purposes, in a constant water current of up to 10 meters per second. This current is generated by a propeller in the lower section of the 120-meter-long tube, driven by one of two ship engines with a combined output of 5,500 horsepower. Ludwig Leo’s design translates this principle into an eccentric late-modernist figure: the vertically oriented annular pipe is held by a laboratory block, raised on steel I-beams, in which the diving basin opens. The principle is based on an inversion of the logic of the 250-meter-long towing channel housed in the neighboring historic building complex, where floating bodies are pulled through still water, likewise for experimental purposes. This facility, first built in 1903 in the context of naval rearmament in the lead-up to the First World War, may itself be understood as an inversion of the still older lock system on the island’s southern flank, where watercraft — at the time primarily barges carrying building materials — were stopped, and lowered or raised. Moreover, the architects of both the building housing the towing channel and the Umlauftank made a pointed contribution to giving the island’s tapering northwestern shore the character of a bow, lending the roughly ship-shaped island the appearance of a stationary floating body gently surrounded by water. Ultimately, however, this makes the densely built-up islet merely a monumental sibling of the houseboats anchored to the north along the opposite bank of the canal.
The walk-through, in dialogue with experts, addresses Ludwig Leo’s Umlauftank, the towing channel, and Schleuseninsel as a site complex that is revealing for the history of architecture, technology, and, not least, Berlin. Multiple temporalities are condensed here: the ambitions of modernist postwar research, the current state of university facilities, and the uncertain future of both research infrastructure and architectural heritage. In addition, different scales and regimes of use are brought into immediate proximity — from the highly precise experiments of fluid dynamics to the slower, more contingent rhythms of communal life along the canal. In this sense, the visit becomes less an act of mere observation than an exercise in situated attention: an opportunity to trace the often invisible relations through which this site is continually being produced anew.
Speaker:
Prof. Dr.–Ing. Paul Uwe Thamsen studied mechanical engineering, specialising in fluid machinery, at the Technical University of Braunschweig, where he also obtained his doctorate. He spent twelve years working for the American group Flowserve, primarily at the Pleuger Wothington plant in Hamburg, first as Head of Research and Development, then as Technical Director, and finally as Managing Director. In 2003, he was appointed professor at the Technical University of Berlin. He heads the Fluid System Dynamics group, specialising in fluid mechanics in machinery and plant. From 2011 to 2014, he also served as First Vice-President of TU Berlin, with responsibility for appointments and research. In 2022, the ASME awarded him the Henry R. Worthington Medal in recognition of his expertise in centrifugal pumps.
Dr. Gregor Harbusch is an architectural historian, freelance writer and deputy editor-in-chief of the online platform BauNetz. He obtained his doctorate (Dr. sc. ETH) from ETH Zurich with a thesis on the architect Ludwig Leo. From 2007 to 2013, he led two research projects at the gta Archive of ETH Zurich on Sigfried Giedion, photography and the fourth CIAM Congress. He is a member of research circles in the fields of architectural and urban history. Harbusch also regularly works as an exhibition curator. For example, he has collaborated with BARarchitekten on projects and documentary films about Ludwig Leo’s legendary circulation tank.
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The Hybrid Lab is a space for work, events and experimentation. The lively place brings together the various project partners, scientists, artists and designers from UdK Berlin and TU Berlin. Inter-, trans- and post-disciplinary projects, events, workshops and seminars are invited to use the space. Please contact our lab coordinator Dr. Michael Fowler for information on use and terms of use at
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