Voluntary 0–100 index covering NOx, SOx, CO₂ and shore-power performance; used by 50+ ports to award port-fee rebates.
Formula
$$ \text{ESI} = 0.35 \cdot \text{NO}_x^\text{avg} + 30 \cdot (1 - s / 0.5) + \text{EEDI bonus} + \text{OPS bonus} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{NO}_x^\text{avg}$ | Average NOx reduction below Tier II baseline, ME + AE | % | NOx Technical File |
| $s$ | Actual bunker sulphur content | % m/m | BDN |
| $EEDI bonus$ | Points for over-performance vs Required EEDI (capped 20) | - | IEE Cert |
| $OPS bonus$ | Up to 5 points for cold-ironing capability and use | - | WPCI |
Score ≥ 30 = standard rebate; ≥ 50 = premium rebate at most participating ports.
Sources
- Environmental Ship Index - environmentalshipindex.org.
- World Ports Climate Initiative.