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CII Corrective Trajectory

Project a ship's attained CII forward over the corrective action plan period under user-set annual improvement assumptions, against the tightening Required CII trajectory and the A-to-E rating boundaries. Identifies the year of expected return to a C rating.

CIICorrective action planReg 28.10

Starting position

Attained CII at trigger yearg CO₂/(cap·nm)The most recent year's attained CII that triggered the corrective action plan.Required CII at trigger yearg CO₂/(cap·nm)The Required CII for the trigger year (from the Required CII calculator).Trigger yearThe calendar year that pulled the trigger (D for 3 consecutive years, or E once).

Corrective measures

Combined CII improvement from corrective measures%Combined non-overlapping savings from all planned corrective measures. Use the SEEMP combined operational measures calculator to compute this from individual measure savings.Implementation yearThe first calendar year in which the full set of corrective measures is operational.Required CII annual tightening%/yrAnnual reduction factor of the Required CII trajectory. 5% per year applies to most ship types from 2023 to 2026; the post-2026 trajectory is to be reviewed at MEPC 86 in 2027.

Year of return to C rating

2027

2 year(s) after trigger; 0 year(s) after implementation.

Attained CII at end of plan

4.55g CO₂/(cap·nm)

Final rating

Plan feasibility

Feasible

Returns to C rating in 2027.

Year-by-year trajectory

Year	Attained CII	Required CII	Ratio	Rating
2025	6.15	5.00	1.23	E
2026	6.15	4.75	1.29	E
2027	4.55	4.51	1.01	C
2028	4.55	4.29	1.06	D
2029	4.55	4.07	1.12	D
2030	4.55	3.87	1.18	D
2031	4.55	3.68	1.24	E

Formula, rating boundaries, and assumptions

The attained CII is held constant at the starting value until the implementation year, then reduced by the combined corrective measure savings s. The Required CII is reduced by the annual reduction factor each year. The rating is determined by comparing the ratio Attained / Required against the standard d-vector boundaries.

Standard d-vector rating boundaries (MEPC.339(76))

Rating	Upper bound (Attained / Required)
A (superior)	≤ 0.86
B (advanced)	0.86 – 0.94
C (compliant)	0.94 – 1.06
D (low minor)	1.06 – 1.18
E (inferior)	> 1.18

Symbol legend

Symbol	Meaning	Unit	Source
$\\text{CII}_a$	Attained CII for year y	g CO₂ / (cap·nm)	computed
$\\text{CII}_r$	Required CII for year y	g CO₂ / (cap·nm)	MEPC.337(76) reference line
$y_0$	Trigger year	year	input
$y_\\text{impl}$	Implementation year	year	input
$s$	Combined corrective-measure savings	fraction	SEEMP combined measures calculator
$r_\\text{annual}$	Annual Required CII reduction factor	fraction	MEPC.338(76)
$d_R$	Rating boundary multiplier	-	MEPC.339(76) Table