How much does a D or E rated ship have to cut its CII?

Formula, assumptions, and limits

An 82,000 DWT bulk carrier rated E for 2025 at an attained CII of 4.500 needs a 15.2% cut to reach C in 2027 and a 20.0% cut to reach the required CII itself. A 20% cut in place from 2027 brings it back to C in 2027 and 2028, but the required line keeps falling and the ship is D again from 2029. The projector works this out from the MEPC.353(78) reference line, the reduction factors of MEPC.338(76) and MEPC.400(83), and the boundaries of MEPC.354(78).

Formula

The required CII for each year is the fixed reference line cut by that year’s factor, and the planned cut applies from the first full year the measures are in place:

The cut the plan needs in the target year, taken here as $T = Y + 2$:

• $Y$: the trigger year, the third consecutive D or the E.
• $p$: the combined cut in attained CII from the planned measures.
• $y_i$: the first full year with the measures in place.
• $d_3$: the C/D boundary multiplier for the ship type, MEPC.354(78) Table 1 (1.06 for bulk carriers).
• $Z_y$: 5% to 11% for 2023 to 2026, then 13.625% to 21.5% for 2027 to 2030.

Derivation

Regulation 28.7 of MARPOL Annex VI requires a plan of corrective actions from a ship rated D for three consecutive years or rated E, and Regulation 28.8 requires the SEEMP to be revised to include it and submitted no later than one month after the attained CII is reported. The 2024 SEEMP Guidelines, MEPC.395(82), which revoked MEPC.346(78), describe what the plan sets out in paragraph 15.4.1: the actions to achieve “at least a C rating for the calendar year following the adoption of the plan of corrective actions and ultimately the required annual operational CII”.

The attained CII is reported within three months of the year end (Reg. 28.2), so on this projector’s reading a plan for a year-Y rating is adopted in Y+1 and its first test year is Y+2. “At least C” means a ratio at or below the C/D multiplier, and “the required annual operational CII” is a ratio of 1.00, the middle of band C (Reg. 28.6). The reference line does not change for the ship, so only Z moves the required CII from year to year.

Assumptions

• The ship’s capacity and type are unchanged over the plan.
• Before the measures take effect, attained CII stays at the trigger year’s figure; from then on it is cut by the planned percentage and held there.
• The planned cut is the combined effect of all measures, without double counting where two measures act on the same fuel.
• The target year is two years after the trigger year. The Regulation sets the reporting and submission deadlines; the year of adoption is the projector’s reading of them.

Worked example

The bulk carrier from the opening, 82,000 DWT with a reference line of 4.167 and an attained CII of 4.500 in 2025:

For C in 2027 the attained CII must be at or below 1.06 × 3.599 = 3.815, a cut of 1 − 3.815 ÷ 4.500 = 15.2%. To reach the required CII of 3.599 it must fall 20.0%. The 20% plan meets both in 2027 and loses C in 2029.

Edge cases and limits

• After 2030. No reduction factor is adopted beyond 2030, so the table stops there and a trigger year of 2029 or later has no target year in range.
• Repeat triggers. Regulation 28.7 does not say whether an E rating resets the count of consecutive D years.
• What the cut means. A percentage cut in attained CII is a cut in CO2 per unit of transport work; a ship that sails further on the same fuel lowers its CII without burning less.

Regulatory basis

MEPC.395(82) of 4 October 2024 sets the plan’s content and has since been amended by MEPC.401(83) and MEPC.413(84). Neither amendment touches the corrective plan, so para 15.4 and its target in para 15.4.1 apply as adopted, and MEPC.347(78) para 5.7 still governs the additional verification of a plan required under MARPOL Annex VI Regulation 28.7.

Common errors

1. Aiming at the C/D edge three years out. The plan’s first test is C in the year after adoption, and its aim is the required CII, a ratio of 1.00.
2. Holding the required CII at the trigger year’s value. It falls every year to 2030 under MEPC.338(76) and MEPC.400(83), so a fixed target is too lenient.
3. Confusing the corrective plan with the three-year implementation plan. Every ship’s SEEMP Part III carries a three-year plan under MEPC.395(82) section 12; the corrective plan of section 15 is the added one for D and E ships.
4. Citing MEPC.346(78). The 2022 SEEMP Guidelines were revoked by MEPC.395(82).

The two cuts a corrective plan has to show

Every plan answers two numbers: the cut that brings the ship to at least C in the year after the plan is adopted, the first aim MEPC.395(82) para 15.4.1 sets for the plan, and the cut that reaches the required CII itself. The gap between them is the upper half of band C, from a ratio of 1.00 to 1.06: 6% of the required CII for a bulk carrier, whose C band runs from 0.94 to 1.06.

The year-by-year table then shows whether the plan holds. Because the required line tightens by 2.1 to 3.2% a year, a one-step cut sized exactly to the C/D edge in the target year is back at D the following year. A plan that has to hold C to 2030 needs either a deeper first cut or a second measure before the ship slips.

Where to find each input

• Trigger year and attained CII: the Statement of Compliance for the year rated E, or for the third consecutive D, issued after the IMO DCS data are verified.
• Capacity: the deadweight or gross tonnage from the ship’s particulars, the same figure the CII calculator uses.
• Planned cut: the combined estimate of the measures listed in the plan, such as speed reduction, hull cleaning or a fuel change, worked out on the same annual basis as the attained CII.
• First full year in place: the first calendar year in which every measure runs for the whole twelve months; a measure fitted at a mid-year drydock counts fully only from the following year.