Carbon compliance is not a calculation problem. The formula is public, the coefficients are published, and any competent engineer can compute an attained carbon intensity figure in a spreadsheet. The problem is the chain of evidence behind that figure — the noon reports it aggregates, the bunker delivery note values it should use rather than defaults, the voyage adjustments and correction factors applied to it, and the ability to demonstrate to a verifier that every input is traceable and unaltered. That is where spreadsheet-based carbon reporting quietly fails, because a number in a cell carries no provenance. Meanwhile the surrounding obligations have hardened: aggregated data goes to the verifier by the end of March each year, the resulting rating is recorded on a Statement of Compliance that lives on board for five years, and an adverse rating triggers a corrective action plan that must be confirmed before that statement can even be issued. With the required reduction tightening every year, vessels comfortably rated today drift downward without operational change. This guide covers the annual data chain, the documents that must exist, the trigger logic behind corrective action, and where spreadsheet reporting breaks. To put carbon reporting on an auditable footing, book a demo or start a free trial.
REPORTING GUIDE · CARBON INTENSITY
CII Rating and EEXI Reporting for Commercial Fleets
From noon report to Statement of Compliance — the annual data chain, the evidence a verifier tests, the SEEMP Part III implementation record, and the trigger logic that turns a rating into a corrective action plan.
Carbon reporting fails on provenance, not arithmetic.
The Annual Data Chain
Carbon intensity reporting runs as a sequence, and each link either preserves or degrades the integrity of what reaches the verifier. Understanding the chain shows where evidence has to be captured rather than reconstructed.
1Operational data capturedFuel consumption by type, distance sailed and hours under way, recorded as operations happen across the reporting year.
2Aggregated for the yearConsolidated into the annual data collection submission covering the full calendar year of operation.
3Attained CII calculatedAnnual carbon dioxide emissions divided by capacity multiplied by distance sailed, with any applicable correction factors and voyage adjustments applied and documented.
4Submitted by 31 MarchAggregated data and the calculated attained CII go to the verifier no later than the end of March following the reporting year.
5Verifier checks integrityThe flag administration or Recognised Organisation examines data integrity, not merely the arithmetic, before the rating is determined.
6Rating and Statement of ComplianceThe attained figure and its A to E rating are recorded on the Statement of Compliance, which is retained on board for five years.
The critical word in step five is integrity. The verifier is not simply recomputing a number; they are assessing whether the inputs are credible and traceable. This is precisely why the carbon coefficients used matter: default values are published for general use, but certified bunker delivery note figures should be substituted where they apply to a regulatory filing. A reporting process that quietly uses defaults because the bunker notes were never linked to the consumption record produces a defensible-looking number built on a weaker foundation than it should be. To capture consumption and bunker evidence together as it happens, book a demo or start a free trial.
The Target Moves Every Year
The most commonly underestimated feature of the regime is that a vessel can hold its performance perfectly steady and still fall through the bands, because the required carbon intensity tightens annually against the 2019 reference line.
20235%
20247%
20259%
202611%
202712.5%
202814.5%
202918%
203021.5%
Reduction required against the 2019 reference line, with the later factors set by resolution and steeper than the original trajectory in order to align with the wider emissions reduction target. The operational consequence is that rating management is forward-looking by necessity: the question is not what a vessel scored last year but which year it is projected to drop a band, and what has to change before then. Industry analysis has suggested a substantial share of the global fleet would fall into the lower bands without operational modification — which is a statement about the tightening denominator as much as about vessel performance.
The Trigger Logic
Ratings themselves carry no direct penalty, but two specific patterns convert a rating into a mandatory obligation with its own deadline and verification requirement.
D for three consecutive years
or
E in any single year
Mandatory corrective action plan
Developed within SEEMP Part III, identifying the causes and specifying the operational or technical measures that will restore a C rating or above. Submission is required within one month of the annual data report, and the plan must be confirmed by the Administration or a Recognised Organisation — before the Statement of Compliance can be issued.
A poor rating is not detainable — a missing plan is a finding
This distinction matters and is often misunderstood. A D or E rating is not in itself a Port State Control detainable deficiency; the regime does not detain ships for carbon intensity performance. What can be flagged is the absence of the mandatory corrective action plan where one was triggered, or a SEEMP Part III that was never revised when required. In other words the enforcement exposure attaches to the documentation obligation rather than the performance, which is exactly why the implementation record deserves as much attention as the rating itself. Vessels that missed the revision deadline for the current period face flag state enforcement and inspection deficiencies on that basis alone.
Reporting that carries its own evidence
Consumption captured as operations happen, bunker documentation linked to the fuel it covers, voyage adjustments recorded with their justification, and SEEMP Part III implementation evidenced rather than asserted — so what reaches the verifier has provenance behind every input.
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What Must Exist On Board
Three document sets carry the carbon compliance position, and each has a different character — one technical and largely static, one a living implementation record, one an annual outcome.
EEXI technical file
The design-side requirement, applying from a lower tonnage threshold than the operational regime. The attained index for the individual ship must sit below the required value, establishing a minimum energy efficiency standard. Where compliance is achieved through limitation of shaft or engine power, the associated monitoring and recording obligations continue in service rather than ending at certification.
Technical, one-time certification with ongoing evidence
SEEMP Part III and its confirmation
Contains the calculation methodology the ship uses, the required carbon intensity over the coming three years, the implementation plan for achieving it, and the procedures for self-evaluation and improvement — retained on board alongside its Confirmation of Compliance. It is revised on a defined cycle, and the revision for the current period was due at the end of 2025.
A living implementation record, not a filed document
Statement of Compliance
Issued after the verifier accepts the annual submission, recording the attained operational carbon intensity and the resulting rating. Retained on board for five years, so a vessel carries a visible multi-year performance history that charterers and inspectors can read.
Annual outcome, retained five years
The middle document is where most operators under-invest. SEEMP Part III is frequently treated as a plan to be produced and filed, when its self-evaluation and improvement procedures imply an ongoing record of what was actually implemented and what effect it had. When a corrective action plan becomes mandatory, that implementation history is the foundation the plan is built on — and a vessel with no evidence of what it tried is poorly placed to explain what it will do differently.
Where Spreadsheet Reporting Breaks
The failure modes are consistent, and all of them are about the chain rather than the formula.
Consumption figures transcribed from noon reports into a workbook, with no link back to the source record a verifier could examine
Default carbon coefficients used throughout because certified bunker delivery note values were never associated with the fuel they cover
Voyage adjustments and correction factors applied without the documented justification that makes them defensible
No audit trail showing who changed a figure, when, or why — so an amended cell is indistinguishable from an original entry
SEEMP Part III implementation actions tracked separately from operations, so what was actually done is reconstructed from memory at revision time
Rating projections calculated once a year rather than monitored through it, leaving no opportunity to change the outcome while the year is still running
That last point carries the most commercial weight. Because the rating is an annual aggregate, performance in the early months is already fixed by the time a year-end spreadsheet reveals a problem. Monitoring the attained figure through the year turns carbon intensity into something manageable — a fuel or routing decision taken in month four can still move the annual outcome, whereas the same insight in month twelve cannot. And the consequences of a poor rating extend beyond the corrective action obligation into charter appeal, exclusion by environmentally selective charterers and asset value, none of which are recovered by explaining the number afterwards. To monitor the position while the year can still be changed, book a demo or start a free trial.
Frequently Asked Questions
What is the annual CII reporting cycle?
Operational data on fuel consumption, distance sailed and time under way is captured through the reporting year, then aggregated into the annual data collection submission. The attained carbon intensity is calculated — annual carbon dioxide emissions divided by capacity multiplied by distance sailed — with any correction factors and voyage adjustments applied. The aggregated data and calculated figure go to the verifier, which is the flag administration or a Recognised Organisation, no later than 31 March following the reporting year. The verifier checks data integrity rather than simply recomputing the arithmetic, the rating from A to E is determined, and a Statement of Compliance is issued recording both the attained value and the rating. That statement is retained on board for five years, giving the vessel a visible multi-year performance record.
What triggers a corrective action plan?
Two patterns. A D rating for three consecutive years, or a single E rating in any one year, requires a corrective action plan to be developed within SEEMP Part III. The plan must identify the causes of the shortfall and specify the operational or technical measures that will restore a C rating or above. Submission is required within one month of the annual data report, and the plan must be confirmed by the Administration or a Recognised Organisation — importantly, before the Statement of Compliance can be issued, so an unaddressed trigger holds up the documentation itself. Because the required carbon intensity tightens annually, a vessel that scrapes a C in one year may face the trigger a year or two later without any change in its own operational performance, which is why rating projection matters more than rating history.
Can a vessel be detained for a poor CII rating?
No. A D or E rating is not in itself a Port State Control detainable deficiency — the regime does not detain vessels on carbon intensity performance. What can be flagged is the documentation obligation attached to it: the absence of a mandatory corrective action plan where the trigger conditions were met, or a SEEMP Part III that was not revised when required. Vessels that missed the revision deadline for the current period face flag state enforcement and inspection deficiencies on that basis alone. The practical implication is that the enforcement exposure sits with the implementation record rather than the performance, so a fleet under commercial pressure on its ratings should be particularly careful that the paperwork obligations are fully satisfied while the operational improvements take effect.
Why does the required carbon intensity keep changing?
Because the regime is built on an annually tightening reduction factor applied against a 2019 reference line, so continuous improvement is structurally required rather than optional. The factor rose through the early years of the regime and continues to steepen, reaching double figures in the middle of the decade and climbing substantially by 2030 under the resolution setting the later trajectory, in order to align with the wider transport-work emissions reduction target. The consequence for operators is that holding performance steady means sliding down the bands over time. Rating management therefore has to be forward-looking: the useful question is which year a currently compliant vessel is projected to drop a grade, and what operational or technical change has to be in place before that point.
What does SEEMP Part III actually need to contain?
It sets out the carbon intensity calculation methodology the ship uses, the required carbon intensity over the coming three years, an implementation plan for achieving it, and procedures for self-evaluation and improvement. It is retained on board together with its Confirmation of Compliance. The part most often under-served is self-evaluation, because it implies a continuing record of what was actually implemented and what effect it had, rather than a plan produced once and filed. That record matters practically as well as formally: when a corrective action plan becomes mandatory, the implementation history is the foundation it is built on, and a vessel with no evidence of what it has already tried is in a weak position to explain convincingly what it will do differently.
How does EEXI differ from CII in reporting terms?
EEXI is a technical, design-side requirement applying from a lower tonnage threshold, under which the attained index calculated for an individual ship must fall below the required value to establish a minimum energy efficiency standard. It is essentially a one-time certification supported by a technical file, whereas carbon intensity is an annual operational measurement with a recurring reporting cycle. The two are not entirely separate in practice, though: where EEXI compliance was achieved through limitation of shaft or engine power, the associated monitoring and recording obligations continue in service rather than ending at certification, and that power limitation directly shapes the operational profile that determines the annual carbon intensity outcome. So the technical file is not simply archived — it sets constraints the operational regime then measures against.
Provenance, Not Arithmetic
The verifier examines data integrity, the required intensity tightens every year, and enforcement attaches to the implementation record rather than the rating. Marine Inspection captures consumption and bunker evidence as operations happen, keeps voyage adjustments documented with their justification, tracks SEEMP Part III implementation as a live record, and surfaces the projected rating while the year can still be changed.
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