A–G letter grade derived from a ship’s EEDI Z-score within its ship-type + size peer group.
Formula
$$ z = \frac{\text{EEDI}\text{peer} - \text{EEDI}\text{ship}}{\sigma_\text{peer}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{EEDI}_\text{ship}$ | Attained EEDI / EEXI of the ship | g / (t·nm) | IEE Cert |
| $\text{EEDI}_\text{peer}$ | Peer-group mean EEDI | g / (t·nm) | RightShip database |
| $\sigma_\text{peer}$ | Peer-group standard deviation | g / (t·nm) | RightShip database |
| $z$ | Z-score | σ | result |
Grade bands (approximate): A ≥ 1.3, B ≥ 0.5, C ≥ −0.5, D ≥ −1.3, E ≥ −2.0, F ≥ −3.0, G below.
Sources
- RightShip - GHG Rating methodology.
- IMO Resolution MEPC.328(76) - EEDI / EEXI.