In June of 2021, the IMO Marine Environmental Protection Committee (MEPC) held its 76th meeting, where they adopted resolution MEPC.328(76) containing amendments to MARPOL Annex VI concerning mandatory goal-based technical and operational measures to reduce carbon intensity of international shipping. Developed under the framework of the Initial IMO Strategy on Reduction of GHG Emissions from Ships agreed in 2018, these technical and operational amendments require ships to improve their energy efficiency in the short term and thereby reduce their greenhouse gas emissions.
From 1 January 2023 it is mandatory for all ships to calculate their attained Energy Efficiency Existing Ship Index (EEXI), to measure their energy efficiency and to initiate the collection of data for the reporting of their annual operational carbon intensity indicator (CII) and CII rating. The attained EEXI shall be calculated for each ship and for each ship which has undergone a major conversion.
The required EEXI value is determined by the ship type, the ship’s capacity and principle of propulsion and is the maximum acceptable attained EEXI value.
The amendments to MARPOL Annex VI are in force from 1 November 2022. The requirements for EEXI and CII certification came into effect on 1 January 2023. This means that the first annual reporting will be completed in 2023, with initial ratings given in 2024.
Vessels impacted by EEXI must demonstrate compliance by their next survey – annual, intermediate or renewal – for the International Air Pollution Prevention Certificate (IAPPC), or the initial survey before the ship enters service for the International Energy Efficiency Certificate (IEEC) to be issued, whichever is the first on or after 1 January 2023.
A ship’s attained EEXI indicates its energy efficiency compared to a baseline. Ships attained EEXI will then be compared to a required Energy Efficiency Existing Ship Index based on an applicable reduction factor expressed as a percentage relative to the Energy Efficiency Design Index (EEDI) baseline. It must be calculated for ships of 400 gt and above, in accordance with the different values set for ship types and size categories. The calculated attained EEXI value for each individual ship must be below the required EEXI, to ensure the ship meets a minimum energy efficiency standard.
The CII figures out the yearly reduction factor that is needed to make sure that a ship’s operational carbon intensity keeps getting better while staying within a certain rating level. The annual operational CII that was actually reached must be written down and checked against the minimum annual operational CII. This lets us figure out the operational carbon intensity grade.
The carbon intensity of a ship will be graded A, B, C, D, or E, with A being the highest. The rating indicates a performance level of major superior, minor superior, moderate, minor inferior, or inferior. The performance level will be documented in a “Statement of Compliance” that will be expanded upon in the ship’s Ship Energy Efficiency Management Plan (SEEMP).
A ship rated D for three consecutive years, or E for one year, will have to submit a corrective action plan to show how the required index of C or above will be achieved. Administrations, port authorities and other stakeholders as appropriate, are encouraged to provide incentives to ships rated as A or B. A ship can run on a low-carbon fuel clearly to get a higher rating than one running on fossil fuel, but there are many things a ship can do to improve its rating, for instance through measures, such as: hull cleaning to reduce drag, speed and routing optimization, installation of solar/wind auxiliary power for accommodation services, installing main engine power limiters etc.
The easiest way to get the energy efficiency index down is to reduce engine power, as vessels’ fuel consumption and emissions, respectively, increase as speed increases. The propulsion power, thus CO2 emissions, is approximately proportional to the cube of the speed. This means that reducing speed by 20% can drop the emitted CO2 by 50%. Slow steaming, therefore, is a more carbon-efficient way to transport goods. The engine power limitation systems can be bypassed, but only if required for the safe operation of the ship, for example, in harsh weather conditions.
The Engine Power Limiter (EPL) must be overideable and will limit engine power by restricting the fuel index to a calculated set value. This restricts the total amount of fuel that can be injected into the engine and thereby limiting the power the engine can produce. For correct installation, the EPL must limit the fuel index to match the engine power for MCRlim.
The Engine Power Limitation (EPL) as such does not alter NOx critical settings or components of the engine.
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. 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 overideable power limitation). Specific fuel oil consumption of the main engine and ship speed are regarded for this specific power.
In conclusion, 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, through correction factors have been introduced to allow a suitable comparison. 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. From a technical perspective, all ship owners and shipbuilding stakeholders must consider and assess how they will support compliance with EEXI. Depending on the vessel age and prospects, some owners and operators may even be scrapping vessels earlier than envisioned.
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Source and Bibliography:
- International Maritime Organization (IMO)
- American Bureau of Shipping (ABS)