CII rating estimator

From 1 January 2023 every ship of 5,000 GT and above engaged in international trade carries an annual operational Carbon Intensity Indicator (CII) rating, A through E. The methodology is set out in MARPOL Annex VI Regulation 28 and IMO MEPC resolutions 336–339(76), with the Z (annual reduction) factor updated by MEPC.355(78).

AER (Annual Efficiency Ratio) is the default attained CII metric:AER = Σ(fuel × Cf) / (DWT × distance)in g CO₂ per DWT·NM. The required CII for the year is the 2019 reference line reduced by the year's Z factor (5% in 2023, ramping by 2% annually). The dd ratio of required to attained then maps to A/B/C/D/E bands.

What the rating means

• A (dd ≥ 1.34) — major superior. Marketing advantage; some charterers offer premium hire.
• B (1.21–1.34) — minor superior.
• C (1.06–1.21) — moderate. The compliance baseline.
• D (0.94–1.06) — minor inferior. Three consecutive D years requires a documented plan of action in SEEMP Part III.
• E (< 0.94) — major inferior. A single E year requires a corrective action plan.

Corrective Action Plan (CAP) template

Three consecutive D ratings or a single E rating requires a CAP submitted with the SEEMP Part III to the Recognised Organisation. Structure per MEPC.355(78) resolution:

1. Root-cause analysis — which drivers pulled the vessel below C (hull condition, port waiting, cargo mix, weather routeing, speed profile, engine tuning)?
2. Target rating — realistic target (at least C, ideally B) for the next 12-month calendar year.
3. Measures selected — from the operational + technical lever list below. Reference the specific SEEMP Part III measure numbers.
4. Timeline — measure-by-measure implementation dates.
5. Monitoring + verification — quarterly review with the DPA; annual verification by the RO.
6. Master + Chief Engineer sign-off — mandatory endorsement per the SEEMP.

The CAP is a live document; each quarterly review updates the RO record. Non-implementation of a signed CAP is treated as a MARPOL Annex VI compliance failure by charterers + PSC alike.

MEPC.354(78) correction factors

Under MEPC.354(78) certain operational conditions can be excluded from the CII calculation via voyage-adjustment factors:

• Weather (fW) — heavy-weather deviation as evidenced by a documented voyage weather log. Reduces the fuel used-attributed to that leg.
• Short-voyage (fS) — voyages under a specified minimum distance. Excludes the port-arrival + departure manoeuvring fuel that inflates AER on short trades.
• Ice-condition (fi) — voyages inside designated ice regions. Recognises the fuel penalty of navigating through ice.
• STS (fSTS) — ship-to-ship transfer operations, particularly relevant for tanker crude-oil transfers.

Correction factors are applied via the DCS reporting; supporting evidence (voyage plans, weather logs, STS records) must be retained for RO verification.

Levers to improve CII

• Slow steaming — fuel burn is roughly cubic with speed; small speed reductions yield large CII gains.
• Voyage optimisation — weather routeing, just-in-time arrival to avoid waiting at anchor.
• Hull and propeller cleaning — biofouling can add 10–15% to fuel burn.
• Energy-saving devices — Mewis ducts, pre-swirl stators, propeller boss cap fins.
• Fuel switching — LNG (Cf 2.750), methanol, ammonia. Note CII is well-to-tank only; LCA-based metrics are coming.
• Cargo distribution / trim optimisation.

See also

• · CO₂ regulation overview — CII, EEXI, EU ETS, FuelEU Maritime, IMO GHG Strategy.
• · NOx Tier I/II/III — separate Annex VI pollutant.
• · EGCS / scrubbers — sulphur compliance, not CO₂.
• · SIRE 2.0 / TMSA — vetting now considers CII.

Last verified 4 months ago