Comprehensive energy efficiency assessment and validation of ship shaft generator and hydrodynamic energy-saving systems under actual operating conditions

Widely used energy efficiency indicators, including the Energy Efficiency Design Index (EEDI), Energy Efficiency Existing Ship Index (EEXI), and Carbon Intensity Indicator (CII), have limitations in assessing the comprehensive energy efficiency of ocean-going ships under actual operating conditions at the design stage. To address this issue, this study proposes an engineering assessment framework for shaft generator and hydrodynamic energy-saving systems and introduces the Energy Efficiency Comprehensive Index (EECI), which incorporates typical shipping routes and actual marine environments. An extendable mathematical model of the ship power system and energy-saving devices is developed and validated against actual operational data. Navigational scenarios are then reduced based on correlations among environmental variables to improve computational efficiency. For a 230,000 DWT bulk carrier, factorial analysis shows that the combined application of the shaft generator, PRH retrofit, and propeller tip trimming reduces EECI by 8.23%. Taking the actual operational CII change as the benchmark, EECI reduces the discrepancy in the estimated retrofit benefit by 63.31% compared with EEXI. These results indicate that EECI provides a more representative design-stage assessment of expected operational energy-efficiency benefits, particularly for ships that do not normally operate at the prescribed design point.