Environmental Ship Index (ESI)
Voluntary NOx, SOx, CO₂ and OPS performance index used by 50+ ports worldwide to award port-fee rebates. Score 0–100; most ports offer rebates above 30 and premium rebates above 50.
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Formula, assumptions, and limits
| Symbol | Meaning | Unit |
|---|---|---|
| Average NOx reduction below Tier II baseline, ME + AE | % | |
| Actual bunker sulphur content | % m/m | |
| Points for over-performance vs Required EEDI (capped 20) | ||
| Up to 5 points for cold-ironing capability and use |
Source: Environmental Ship Index - *environmentalshipindex.org*; World Ports Climate Initiative
In short
Compute a ship's Environmental Ship Index score for NOx, SOx, CO₂ and shore-power performance - port-fee rebate qualifier.