Improving the energy efficiency of ships


In order to reduce shipping's impact on climate change, IMO has started in the early 2000s to consider technical and operational measures to improve the energy efficiency of ships.

In 2011, IMO adopted amendments to MARPOL Annex VI to mandate technical and operational energy efficiency measures to reduce the amount of CO2 emissions from international shipping.

The Energy Efficiency Design Index (EEDI) and the Ship Energy Efficiency Management Plan (SEEMP) entered into force on 1 January 2013. Those measures represent the first global mandatory GHG-reduction regime for an international industry sector and have been driving energy efficiency improvements across the global fleet for more than a decade. Goal-based and technology-neutral regulations have incentivized the use of energy-efficient technologies such as hull air lubrication, wind assisted propulsion, waste heat recovery, etc.

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IMO Member States have adopted further energy efficiency measures in 2021 to reduce the carbon intensity of international shipping by at least 40% in 2030 compared to 2008.

Continuous improvements in the energy efficiency of shipping remains crucial, and will help to absorb the extra cost of alternative low- and zero-carbon fuels.

Energy Efficiency Design Index (EEDI)

The EEDI is an important technical measure aiming at promoting the use of more energy efficient equipment and engines for the design of new ships in order to make them less polluting. The EEDI requires a minimum energy efficiency level per capacity mile (e.g. tonne mile) for different ship type and size segments.

Since 1 January 2013, following a two-year transitional phase, new ship design needs to meet the reference level for their ship type. The level is to be tightened incrementally every five years, and so the EEDI is expected to stimulate continued innovation and technical development of all the components influencing the fuel efficiency of a ship from its design phase. The EEDI is a non-prescriptive, performance-based mechanism that leaves the choice of technologies to use in a specific ship design to the industry. As long as the required energy efficiency level is attained, ship designers and builders are free to use the most cost-efficient solutions for the ship to comply with the regulations. The EEDI provides a specific figure for an individual ship design, expressed in grams of carbon dioxide (CO2) per ship's capacity-mile (the smaller the EEDI, the more energy efficient the ship design) and is calculated by a formula based on the technical design parameters for a given ship. 

The CO2 reduction level (grams of CO2 per tonne mile) for the first phase is set to 10% compared to a reference line calculated from the average efficiency for ships built between 2000 and 2010. It is tightened every five years to keep pace with technological developments of new efficiency and reduction measures until 2025 and onwards when a 30% reduction is mandated for applicable ship types.

The EEDI was originally developed for the largest and most energy intensive segments of the world merchant fleet and embraces emissions from new ships covering the following ship types: tankers, bulk carriers, gas carriers, general cargo ships, container ships, refrigerated cargo carriers and combination carriers. In 2014, MEPC adopted amendments to the EEDI regulations to extend the scope of EEDI to: LNG carriers, ro-ro cargo ships (vehicle carriers), ro-ro cargo ships; ro-ro passenger ships and cruise passenger ships having non-conventional propulsion. These amendments mean that ship types responsible for approximately 85% of the CO2 emissions from international shipping are incorporated under the international regulatory regime.

For a uniform and effective implementation of the regulations, guidelines related to the EEDI (regulation 22 of MARPOL Annex VI) and survey and certification (regulation 5) were developed by MEPC. They are available in the Index of MEPC Resolutions and Guidelines and Circulars related to MARPOL Annex VI under the "Guidelines and Circulars related to MARPOL Annex VI" part.

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Ship Energy Efficiency Management Plan (SEEMP)

The Ship Energy Efficiency Management Plan (SEEMP) is an operational mechanism to improve the energy efficiency of a ship in a cost-effective manner. The SEEMP urges the ship owner and operator at each stage of the plan to consider new technologies and practices when seeking to optimise the operational performance of a ship. The SEEMP also provides an approach for shipping companies to manage ship and fleet efficiency performance over time using recognized monitoring tools.

The 2022 guidelines for the development of the SEEMP incorporates best practices for fuel efficient ship operation as well as templates for the development of SEEMPs, which should comprise of three parts:

  • Part I: Ship management plan to improve energy efficiency

  • Part II: Ship fuel oil consumption data collection plan

  • Part III: Ship operational carbon intensity plan

Data collection system (DCS) for fuel oil consumption of ships

In October 2016, MEPC 70 adopted, by resolution MEPC.278(70), mandatory MARPOL Annex VI requirements for ships to record and report their fuel oil consumption in order to have the necessary data to make decisions on further measures to improve the energy efficiency of ships.

More information here.

IMO short-term GHG reduction measures (EEXI, CII rating and enhanced SEEMP)

In 2021, IMO adopted a new set of technical and operational measures (resolution MEPC.328(76)), namely the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII) which enter into force on 1 January 2023.Picture3.png


Energy Efficiency Existing ship Index (EEXI) and Carbon Intensity Indicator (CII) rating

These technical (EEXI) and operational (CII) requirements were adopted in June 2021 as a short-term measure under the Initial IMO GHG Strategy framework for implementation before 1 January 2023.

Under the EEXI framework, all existing ships of 400 GT and above are required to calculate their attained Energy Efficiency Existing Ship Index (EEXI), which reflects the "technical" or "design" efficiency of the ship. Ships then have to reach a "required EEXI", equivalent to Required EEDI levels for 2022, thus creating a level-playing field among the fleet.

The EEXI framework is technology neutral, and the shipowner or charterer can choose the most appropriate means to achieve the goals set by IMO regulations. Existing technologies available to comply with the Required EEXI are engine/shaft power limitation, waste heat recovery, wind assisted propulsion, etc.

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The Carbon Intensity Indicator (CII) rating reflects the operational energy efficiency of ships, building upon fuel oil consumption from the IMO DCS and the SEEMP as a management tool. CII is mandatory for ships of 5,000 gross tonnage and above. The attained annual operational CII has to be documented and verified against the required annual operational CII. The annual carbon intensity reduction factor is equivalent to business-as-usual until entry into force; then 2% from 2023 to 2026; and to be further strengthened for the period 2027 to 2030.

Based on this, the ship's Administration determines the operational carbon intensity rating of the ship.  The rating is given on a scale - operational carbon intensity rating A, B, C, D or E - indicating a major superior, minor superior, moderate, minor inferior, or inferior performance level. A ship rated D for 3 consecutive years or rated as E, shall develop a "Plan of corrective actions".

The CII framework provides tools for Administrations, ports and other stakeholders, including the financial sector, to provide incentives to most energy efficient ships.
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