Closing energy efficiency gaps in shipping requires understanding seafarers’ operations in route planning and their preferences for assistive technology. The objective of this research was to systematically examine seafarers’ decision-making to inform human-centered decision support systems (DSSs). We conducted a hierarchical task analysis based on guidelines and expert interviews (Study 1, N = 3) and assessed key tasks using seafarers’ expectancy-value-cost ratings (S2, N = 65) via online surveys. Tidal and weather routing tasks were rated highest for energy efficiency, despite associated costs. We further examined psychological need satisfaction and preferences for human versus automated control, finding autonomy satisfaction rated significantly lower than other needs; seafarers preferred automated information processing but retained human control over decisions. Finally, post-route planning interviews using the critical decision method (S3, N = 22) highlighted the complexity of balancing goals, particularly safety, and emphasized practical experience as key in route planning and system use. All studies underscored the need for high transparency and controllability in system information and functions. Our research emphasizes understanding seafarers’ perceptions of energy-efficient operations and integrating automated support into current processes.