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.

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 updated 2026-04-27