In recent years, there has been an increasing focus on energy-efficient operation of vessels. The International Maritime Organization has launched several initiatives for reducing emissions from ships. One of these is the ‘Ship Energy Efficiency Management Plan’, SEEMP. This paper focuses on the operational level of the SEEMP and how the SEEMP can efficiently support the crew in performing energy efficient operations. The study is based on analyses of two vessels employed in the oil & gas and wind industry and uses qualitative methods based on 30 semi-structured interviews with seafarers and office employees, combined with document analysis of IMO’s guidelines for development of the SEEMP along with the vessels’ SEEMPs. The study shows that operation of these vessels is very irregular and is influenced by many actors. The officers on board find that many goals or demands conflict with energy-efficient operation. To make the SEEMP useful as a dynamic tool, it is therefore of great importance to involve stakeholders and crew in defining unambiguous goals and making the entire system around the ship cooperate in meeting these goals.