The calculation of the EEXI follows the calculation of the well-known EEDI. It is based on the 2018 calculation guideline of the EEDI, with some adaptations for existing vessels. Specific EEXI-related mandatory guidelines published by the IMO are:
- RESOLUTION MEPC.333(76) 2021 GUIDELINES ON THE METHOD OF CALCULATION OF THE ATTAINED ENERGY EFFICIENCY EXISTING SHIP INDEX (EEXI)
- RESOLUTION MEPC.334(76) 2021 GUIDELINES ON SURVEY AND CERTIFICATION OF THE ATTAINED ENERGY EFFICIENCY EXISTING SHIP INDEX (EEXI)
- RESOLUTION MEPC.335(76) 2021 GUIDELINES ON THE SHAFT / ENGINE POWER LIMITATION SYSTEM TO COMPLY WITH THE EEXI REQUIREMENTS AND USE OF A POWER RESERVE
In principle, the EEXI describes the CO2 emissions per cargo ton and mile. It determines the standardized CO2 emissions related to installed engine power, transport capacity and ship speed. The EEXI is a design index, not an operational index. No measured values of past years are relevant and no on-board measurements are required; the index only refers to the design of the ship.
The emissions are calculated based on the installed power of the main engine, the corresponding specific fuel oil consumption of the main engine and of auxiliary engines (taken from the engine test bed), and a conversion factor between the fuel and the corresponding CO2 mass. The transport work is determined by capacity, which is usually the deadweight of a ship and the ship speed related to the installed power.
The calculation does not consider the maximum engine power, but for most ship types it is 75% of MCR or 83% of MCRlim (in case of an installed overridable power limitation). Specific fuel oil consumption of the main engine and ship speed are regarded for this specific power.
The EEXI is applied to almost all ocean going cargo and passenger ships above 400 gross tonnage. For different ship types, proper adjustments of the formula have been introduced to allow a suitable comparison. This is performed by correction factors. Several correction factors are defined to correct the installed power, such as for ice-classed ships, as well as to correct the capacity, for instance to consider structural enhancement. Further correction factors are applicable for cranes on board and for ice-classed ships having IA Super and IA.
With all these correction factors being applicable only for specific ship types, the initially simple calculation of the EEXI might become quite complex for some ships. In order to support you with this sometimes complex task, DNV has created two potential solutions: a digital self-service tool and the interactive, expert-led route. DNV's Maritime Advisory, with many years and several hundred cases of experience in the calculation of the EEDI, offers reliable, accurate and profound determination of the EEXI attained for each ship, which is subject to EEXI regulations.