Understanding CII and EEXI
The Carbon Intensity Indicator (CII) and the Energy Efficiency Existing Ship Index (EEXI) are two complementary measures. The International Maritime Organization introduced them through amendments to MARPOL Annex VI. Together, they represent the IMO's strategy for reducing greenhouse gas emissions from international shipping. They address both the operational and technical dimensions of ship energy efficiency.
Both measures took effect on January 1, 2023. This marked a major step in the maritime industry's decarbonization journey.
CII, adopted through resolution MEPC.352(78), measures a ship's operational carbon intensity. That is 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. 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. It applies to existing ships of 400 gross tonnage and above. It establishes whether a ship's design-level energy efficiency meets the required standard. The standard is based on the ship's type, size, and installed propulsion power.
Ships that do not meet the required EEXI value must make technical changes to bring their attained EEXI into compliance. Examples are engine power limitation or installing energy-saving devices.
The CII Rating Scale
The CII rating system assigns each ship a grade from A to E. The grade comes from comparing its attained carbon intensity with the required CII value for that ship type and size. An A rating indicates a ship is performing far better than the required level. 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. A ship must improve its operational efficiency year over year to keep the same rating.
The consequences of poor CII ratings grow over time. Ships rated D for three consecutive years, or rated E in any single year, must develop a corrective action plan. The plan is part of their Ship Energy Efficiency Management Plan (SEEMP).
This plan must outline concrete operational and technical measures. They must bring the vessel's carbon intensity back to an acceptable level. The first mandatory corrective actions are expected from 2026. They are based on ratings built up since the system began in 2023.
Beyond regulation, CII ratings increasingly influence commercial decisions. Charterers, cargo owners, and port authorities are starting 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. This makes 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. The formula 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. The ship's attained EEXI must not exceed this threshold. The calculation is performed once. 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). It reduces the maximum continuous rating of the main engine through an overridable power limit.
Other options include shaft power limitation and installing energy-saving devices. Examples of such devices are wind-assisted propulsion and air lubrication systems. In some cases, ships can also use 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. Both the technical and operational sides of energy efficiency are covered.
How Navatom Manages CII & EEXI
Navatom calculates each vessel's attained CII continuously. It uses the daily fuel consumption the engine room records in Logbooks. It also uses 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. It shows the current rating trajectory on the fleet dashboard.
This gives shore-based managers an immediate view of which vessels are on track for a good rating. It also shows which ones need action.
The platform's simulation tools let operators model the impact of different strategies on CII performance. They can do this 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. This identifies the most effective improvement measures.
These insights feed directly into the vessel's SEEMP. Navatom manages it as a living document within the platform. It links planned measures to observed performance outcomes.
For EEXI compliance, Navatom stores each vessel's attained and required EEXI values in the vessel profile. They sit alongside its technical specifications. The Planned Maintenance System module tracks any engine power limitation systems or energy-saving devices installed to meet EEXI requirements. This keeps these changes maintained and their effectiveness documented.
When CII or EEXI documents must be submitted to the flag state, Navatom generates the required reports. It also keeps a complete audit trail.