Improving the efficiency of energy consumption, conversion, and transmission on merchant ships has become a critical challenge due to rising fuel costs, increasingly stringent environmental regulations, and the introduction of operational efficiency requirements such as the IMO CII. Existing energy-efficiency metrics are predominantly based on absolute or design-oriented indicators and do not adequately capture the latent reserves of energy savings embedded in ship energy systems. This study addresses this gap by proposing a methodological framework for quantifying energy efficiency through the concept of relative energy-saving potential. The proposed approach integrates ship energy balance analysis with a hierarchical assessment of relative theoretical, technical, and economically feasible energy-saving potentials. The framework is demonstrated using an illustrative numerical example for a representative medium-size product tanker. The presented calculations are intended to demonstrate the applicability of the methodology rather than to provide vessel-specific operational recommendations. The results indicate that a significant share of energy losses can be identified and reduced by technical and economic feasibility considerations. The study concludes that relative energy-saving potentials offer an effective and scalable foundation for ship energy management, supporting SEEMP implementation, CII compliance strategies, and integration into digital twin and AI-based energy management systems.
Holovan et al. (Sun,) studied this question.