Energy efficiency is a key element for reduced shipping emission to meet future environmental regulations. Both design and operation play an important role to meet this goal and the perfection of the interplay between these aspects promises quick improvements to meet the requirements of short term emission standards. The MariData project [https://maridata.org] developed a forward-looking energy management and decision support system (DSS) for ship operation based on rational methods and data created during ship design and sets out to bridge the gap between design and optimizedoperation. The “digital performance twin” of a vessel, which is based on design data, is enhanced with lifecycle data covering the entire operational envelope and provides valuable feedback into design processes.