CII is an operational efficiency indicator that measures a vessel’s carbon intensity over time. It regulates the real-life CO2 emissions from ships and applies to cargo, RoPax, and cruise vessels above 5,000 GT trading internationally from January 1, 2023[1].

Key Features

• Measures CO2 emissions in grams per cargo-carrying capacity and nautical mile
• Annual reporting based on actual fuel consumption
• Ships receive an annual rating from A (best) to E (worst)
• Rating thresholds become increasingly stringent towards 2030

CII Calculation

The formula for CII is:

CII = CO2 Emission / (Dead weight × Distance Sailed)

CII Ratings

Rating	Performance Level
A	Major superior
B	Minor superior
C	Moderate
D	Minor inferior
E	Inferior

Note: C rating is the minimum acceptable rating[1].

Methods to Improve CII Rating

Improvement Methods

• Slow steaming
• Using slide type fuel valves
• Implementing eco nozzles
• Engine derating
• Low load optimization tuning

Deterioration Suppression Methods

• Chief load limiter
• Auto speed reduction in rough seas
• Auto engine load control
• Adaptive sea condition control governor
• PMI auto tuning