In 2018, international shipping became the first industry segment to reach an accord on greenhouse gas (GHG) emissions. The IMO’s 180 Member States committed to a global 40% energy efficiency improvement by 2030 and a 50% improvement in absolute CO2 emissions by 2050 as compared to 2008 values.

Historically, the IMO regulatory framework has evolved around a few ship types – bulk carriers, tankers and containerships – that represent the majority of world trade and therefore most of shipping’s CO2 emissions. However, the methodologies developed for homogenous deep-sea vessels do not necessarily fit well with the much more diverse segment of ro-ro ship types, which have very different capabilities in reaching CO2 reductions.


The IMO has set 1 January 2023 for the implementation of two new compliance instruments – the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII). Under this extreme timescale, all discussion and ratification is to be finalised by June 2021.


This is basically a copy/paste of the Energy Efficiency Design Index (EEDI) introduced for new designs since 2015. Existing ships will likewise have to be certified to a technical efficiency standard, or lose their licence to operate. The EEXI is highly unusual in being a retroactive requirement – it obliges ships built before EEDI Phase 2 (from 2020) to match this level. An EEXI Technical File recording a ship’s emissions reduction rates must be in place by the first annual, intermediate or renewal survey after 1 January 2023.

Put simply, the EEXI is a measure of a ship’s installed power and its speed when using a given proportion of this power. For ships that exceed EEXI restrictions, the most common mitigating measure will be Engine Power Limitation (EPL), a system that suppresses main engine rpm except in emergency situations. EPL will likely enable an average speed reduction among single-engine vessels, but is unlikely to improve the operational profile of most ferries, which require significant power redundancy through multi-engine installations.

Due to the uniquely diverse range of ro-ro type designs and operations, Interferry has always maintained that the EEDI is not a fair way to regulate energy efficiency for newbuilds, so it would be correspondingly inappropriate to impose the same methodology on existing ships. The IMO has recognised this by agreeing that the EEDI Phase 2 reduction rate for ro-ro cargo and ro-ro passenger ships should be only 5% more stringent than Phase 1, as opposed to the 20% mandated for most other shipping segments.


In addition to one-off EEDI or EEXI technical certification, ships must thereafter conform to the CII, a continuous improvement plan for operational efficiency. A ship’s annual output of CO2 per ton per nautical mile will be documented and compared with the average performance for that ship type in the base year 2008, with a general requirement to better the 2008 value by 40%. A ship that falls short must improve performance during the following year(s) until it meets the target.

This can be achieved in several complementary ways, typically by reducing fuel consumption through technical and operational measures. Since the target is to reduce CO2 output, it will also be particularly relevant to explore solutions such as low-carbon fuels, hybrid propulsion and using shore power at berth. As such, the introduction of the CII will affect the operational profile of many ships.


Given how quickly these new instruments have had to be developed, some fundamental challenges still need to be resolved at two upcoming IMO meetings, each being held remotely. The inter-sessional working group on GHG reductions will meet from May 24-28. The deliberations then conclude at the Marine Environment Protection Committee meeting from June 10-17 (MEPC76).

Interferry has submitted the following special requests to these sessions:

  1.  High Speed Craft are currently bundled up with conventional ro-pax ships in the CII dataset. Interferry wants separate treatment for HSC because they are a fundamentally different ship type whose energy efficiency cannot be measured on the same basis as mono-hull steel ships
  2. The dataset for ro-ro cargo ships includes the con-ro sub-segment. This really skews the statistical average since almost all the large ships – more than 25,000 DWT – are con-ro vessels, making CII compliance all the more difficult for pure ro-ro cargo ships. Interferry has therefore proposed that the ro-ro cargo fleet is defined in two parts, below and above this tonnage
  3. Development of the CII included discussions on how to measure capacity for the different ship types, but a decision has yet to be taken. Interferry has requested that GT rather than DWT should be used for all ro-ro types, after conducting analysis showing this was a fairer basis for implementation on such vessels


MEPC 76-7-14 – Establishing High Speed Craft as a new sector in the CII framework

ISWG-GHG 8-3 – Choice of metrics for capacity for ro-ro cargo ships and using a GTDWT-distinction for the ro-ro cargo sector