STUDY A vessel’s cooling water system is one of the main consumers among the auxiliary systems, requiring roughly a third of the electrical energy on board. In cooperation with a large shipping company, the maritime service consultancy FutureShip, a GL company, carried out an investigation of the cooling water circuit in the engine room of a post-Panamax container vessel to analyse potential energy and cost savings by changing the system’s architecture and implementing operational flexibility. In the following article, FutureShip’s Dr Jörg Lampe and Malte Freund describe the scope of the applied simulation, measurements and results.