Inland navigable waterways are significant in cargo transport and leisure activities. In parallel, these channels and rivers often suffer from the ship traffic, as the generated waves may damage waterway banks, along with their riparian fauna. As a consequence, speed limits have commonly been introduced. In some cases, adaptations on the vessel might be more appropriate as an alternative. This paper describes a flap that is mounted at the stern of a barge and is operated by a pusher tug. The barge is used to transport around 170 tons of waste per course from the City of Geneva (Switzerland) to an incineration plant. The optimum shape of the flap was derived from numerical and physical modeling, and its effect tested in situ. The latter indicated that, on site, the wave energy at 20 m distance to the convoy was reduced by half with the use of the flap.