Understanding CII and EEXI
The Carbon Intensity Indicator (CII) and the Energy Efficiency Existing Ship Index (EEXI) are two complementary measures introduced by the International Maritime Organization through amendments to MARPOL Annex VI. Together, they represent the IMO's strategy for reducing greenhouse gas emissions from international shipping by addressing both the operational and technical dimensions of ship energy efficiency. Both measures took effect on January 1, 2023, marking a significant step in the maritime industry's decarbonization journey.
CII, adopted through resolution MEPC.352(78), measures a ship's operational carbon intensity — how many grams of CO2 it emits per unit of cargo-carrying capacity per nautical mile. It applies to ships of 5,000 gross tonnage and above on international voyages. Unlike static design metrics, CII reflects how a ship is actually operated: its speed, routing decisions, cargo utilization, and fuel management all influence the outcome. Each ship receives an annual rating, and the threshold for each rating grade tightens over time to drive continuous improvement.
EEXI, adopted through resolution MEPC.350(78), is a one-time technical assessment that applies to existing ships of 400 gross tonnage and above. It establishes whether a ship's design-level energy efficiency meets the required standard based on its type, size, and installed propulsion power. Ships that do not meet the required EEXI value must implement technical modifications — such as engine power limitation or the installation of energy-saving devices — to bring their attained EEXI into compliance.
The CII Rating Scale
The CII rating system assigns each ship a grade from A to E based on its attained carbon intensity relative to the required CII value for that ship type and size. An A rating indicates a ship is performing significantly better than the required level, while an E rating means the ship's carbon intensity is well above the acceptable threshold. The boundaries between rating grades are defined by reduction factors that tighten annually, meaning a ship must improve its operational efficiency year over year to maintain the same rating.
The consequences of poor CII ratings become increasingly significant over time. Ships rated D for three consecutive years or rated E in any single year are required to develop a corrective action plan as part of their Ship Energy Efficiency Management Plan (SEEMP). This plan must outline concrete operational and technical measures to bring the vessel's carbon intensity back to an acceptable level. The first mandatory corrective actions are anticipated from 2026, based on ratings accumulated since the system began in 2023.
Beyond the regulatory requirements, CII ratings are increasingly influencing commercial decisions. Charterers, cargo owners, and port authorities are beginning to factor CII performance into their selection criteria. Ships with favorable ratings may receive preferential berthing, reduced port fees, or priority in charter negotiations. The data underpinning CII calculations closely mirrors what is collected for EU MRV reporting , making integrated data management essential for operators navigating both obligations.
EEXI: The Technical Baseline
While CII addresses how a ship is operated, EEXI addresses how it was built. The Energy Efficiency Existing Ship Index is calculated using a formula that considers the ship's installed main engine power, specific fuel consumption, and design speed, among other parameters. Each ship type has a required EEXI value based on its deadweight tonnage or gross tonnage, and the ship's attained EEXI must not exceed this threshold. The calculation is performed once, and compliance is verified at the first annual, intermediate, or renewal survey on or after January 1, 2023.
Ships that do not meet the required EEXI value have several options for compliance. The most common approach is Engine Power Limitation (EPL), which reduces the maximum continuous rating of the main engine through an overridable power limit. Other options include shaft power limitation, the installation of energy-saving devices such as wind-assisted propulsion or air lubrication systems, and in some cases, the use of alternative fuels with lower carbon content.
It is important to understand that EEXI compliance does not exempt a ship from CII obligations. A vessel may pass its EEXI assessment but still receive a poor CII rating if it is operated inefficiently. Conversely, a ship with a marginal EEXI may achieve excellent CII performance through careful speed management and optimized routing. The two measures work together to ensure that both the technical and operational aspects of energy efficiency are addressed.
How Navatom Manages CII & EEXI
Navatom calculates each vessel's attained CII continuously using real-time fuel consumption data from the Consumption and Waste module and voyage records including distance sailed, cargo carried, and time at sea. The platform compares the attained CII against the required value for each ship type and displays the current rating trajectory on the fleet dashboard. This gives shore-based managers immediate visibility into which vessels are on track for a favorable rating and which require intervention.
The platform's simulation tools allow operators to model the impact of different operational strategies on CII performance before committing to a course of action. Adjustments to speed profiles, ballast voyage management, and fuel selection can be tested against the current rating trajectory to identify the most effective improvement measures. These insights feed directly into the vessel's SEEMP , which Navatom manages as a living document within the platform, linking planned measures to observed performance outcomes.
For EEXI compliance, Navatom stores each vessel's attained and required EEXI values alongside its technical specifications in the vessel profile. The Planned Maintenance System module tracks any engine power limitation systems or energy-saving devices installed to meet EEXI requirements, ensuring that these modifications are maintained and their effectiveness is documented. When CII or EEXI documentation must be submitted to the flag state, Navatom generates the required reports and maintains a complete audit trail.