Advances in Quantifying the Efficiency of Energy Consumption, Conversion, and Transmission on Merchant Ships

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 abso-lute 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 economical-ly feasible energy-saving potentials. The methodology is demonstrated through an illustrative case study of a medium-size product tanker, focusing on the main engine, auxiliary generators, pumping systems, and HVAC loads. The results indicate that a significant share of energy losses can be systematically identified and progressively constrained by technical and economic feasibility considerations, providing a transparent basis for prior-itizing energy efficiency measures. 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.