The first step to improve an attained EEXI value is to replace the conservative approximated reference speed and the standard values of the specific fuel oil consumption with measured model test and shop test data. Eventually, model test data might be substituted by numerical calculations.
When, after applying individual data based on the documents provided, a gap between the attained EEXI value and the required EEXI value still remains, the design does not comply with the EEXI requirements and changes to the design are needed. This might be the installation of energy efficiency technologies or a limitation of the installed main engine power.
Popular energy efficiency technologies are energy-saving devices such as ducts or propeller boss cap fins, which increase the reference speed for constant installed power. According to current draft calculation guidelines, the effectiveness of these devices is to be determined by model tests. Based on our experience, DNV GL's maritime advisory can estimate the improvement of the attained EEXI value by the potential installation of different energy-saving devices.
The solution chosen most often for improving the attained EEXI is engine power limitation. With the restriction of the available propulsion power, the main engine power value applied in the EEXI formula decreases, but at the same time the reference ship speed decreases and specific fuel oil consumption increases as well. The required level of the engine power limitation is to be determined by an iterative calculation.
DNV GL's maritime advisory offers to calculate the required level of engine power limitation accurately to avoid excessive limitation of the propulsion power. We also provide the level of required engine power limitation to comply with EEXI requirements. Based on this result, the engine’s manufacturer or a certified supplier can determine the corresponding restriction of the fuel rack or the injected fuel amount.