While the maritime sector seeks to reduce its climate footprint with operational measures, onboard energy efficiency is confronted with internal and external constraints. The objective of the current study was to improve understanding of ship crew’s cognition, emotion, and motivation regarding energy-efficient operations in the face of a complex system. Utilizing a mixed method approach, we conducted an interview study onboard a container vessel (N = 14) and an online survey of seafarers (N = 74). Using Thematic Analysis for the interview data, we identified four themes (Stressors, Strategies, Influence, and Motivation), with the latter two themes explored with rating data in the survey. This revealed that concerns for the environment or one’s shipping company were motivating, that the perception of conflicting orders or lack of knowledge were perceived as hindering, and that influence was seen as split between external stakeholders and onboard crews. We discuss how our findings and concepts such as psychological basic needs can be used to develop decision support systems or inform policy, especially by increasing transparency and understandability, e.g. of constraints such as charter contracts.