What is EEXI?

Energy Efficiency existence ship Index (EEXI) formulated for existence vessels, is an index that estimates grams of CO2 per transport work (g of CO2 per tonne‐mile). It can be expressed as the ratio of “environmental cost” divided by “Benefit for Society”. From 1 January 2023 it will be mandatory for all ships to calculate their attained EEXI to measure their energy efficiency.

It is a function of :  Installed power,   Speed of vessel, and Cargo carried.
The philosophy behind EEXI is that its computation be simple and capable of broad application, and promote efforts by all stakeholders to reduce CO2 emissions by reflecting a ship’s energy efficiency in actual use.It stimulates continued technical development of all the components influencing the fuel efficiency of a ship. It also separates the technical and design‐based measures from the operational and commercial ones.

The GHG study conducted by IMO in 2000 resulted into an operational CO2 index. It was accepted at IMO that such an index should reflect only the technical aspects such as the optimization of engines, hull and propeller or the use of non‐fossil fuels, and not the operational or commercial aspects. This led to the refinement of the index. After much deliberation in its Marine Environmental Protection Committee’s various sessions, the current empirical formulation was accepted.

EEXI attained Formula – Parameters: 

Parameter	Description
	Non‐dimensional conversion factor between fuel consumption and CO2emission
	Ship speed in nautical miles per hour
Capacity	Computed as a function of Deadweight as indicated in 2.3 and 2.4 of MEPC 245(66) “2014 Guidelines on the calculation of the Attained EEDI for new ships”
	75% of the main engine MCR in kW
	Auxiliary Engine Power
	Output of innovative mechanical energy efficient technology for propulsion at 75% main engine power
	75% of rated power consumption of shaft motor
	Auxiliary power reduction due to innovative electrical energy efficient technology
SFC	Certified Specific Fuel Consumption in g/kWh
	Correction factor to account for shipspecific design elements. (For e.g. ice classed ships, shuttle tankers)
	Non dimensional coefficient indicating the decrease of speed in representative sea condition of wave height, wave frequency and wind speed
	Capacity factor for any technical/regulatory limitation on capacity
	Cubic capacity correction factor (for chemical tankers and gas carriers)
	Factor for general cargo ships equipped with cranes and other cargo‐ related gear to compensate in a loss of deadweight of the ship
	Availability factor of innovative energy efficiency technology

The EEXI expresses the impact to environment from shipping Vs the benefit to society from shipping. The EEXI formula takes into consideration special design features and needs, including the use of energy recovery, the use of low carbon fuels, performance of ships in waves and the need for ice strengthening of certain ships. The handling of certain design features such as electric propulsion is still subject to evaluation. The EEXI has a constant value that will only be changed if the design is altered. There are some ship types where the EEXI, in units per nautical‐mile, may be considered less meaningful or relevant. This, and the possible need for a minimum size threshold, suggests that the units in which EEXI is measured may need modification to address some ship types and ship sizes, and that the EEXI may not be practically applicable to all ship types. However, large cargo ships can be covered and these ships account for a significant share of emissions.

Baseline :

A reference line (baseline) is defined as a curve representing an average index value fitted on a set of individual index values for a defined group of ships. The baseline formula is given below:

a, b, and c are defined as table below for different type of vessels:

Source: WWW.IMO.ORG