ENERGY EFFICIENCY INDEX STATISTICAL ANALYSIS THROUGH VESSEL OPERATING DATA

IMO is introducing two different emission indexes for a vessel: the Energy Efficiency Design Index (EEDI) and the Energy Efficiency Operational Indicator (EEOI). The former will be used to assess the design of the vessel, the latter would be used to evaluate the vessel in operation. Both indexes represent the ratio between emissions, in mass of CO2, and the transported cargo quantity per sailed distance. At moment an important debate is focusing on the definition of the 'baseline' values for different ship categories. The operational indicator EEOI is a function of the vessel operating data. As showed in published works, sister ships may have completely different Energy Efficiency Operational Indicators, in some cases the difference is even 50%. This gap is due to the different operating conditions of the vessels, due to different trade routes, different load conditions and different sea states. The Department of Naval Architecture, Marine Engineering and Electrical Engineering of the University of Genova carried out in the past a preliminary study aimed at evaluating the carbon footprint of RoPax vessels, and analysed various aspects affecting the carbon dioxide emissions from both technology and fleet energy management techniques points of view. Starting from that experience, the authors developed further activities, whose purpose was to evaluate the EEOI variability through the statistical analysis of the main operating variables of the vessel. A RoPax ship has been used as test case. For this ship a complete series of data concerning two years of navigation for the commercial trade in the Mediterranean Sea were collected. The results of the study are presented in the paper and could represent a useful support for the definition of the future IMO baseline, identifying a possible variation range of the efficiency indicator for a best practice managed RoPax ship.