The existing-ship analogue of EEDI. Same formula, but the reference speed V_ref is derived at 75 % of the limited engine power (via EPL or ShaPoLi), which tightens the denominator and forces older ships into compliance without a full retrofit.
Formula
$$ \text{EEXI}\text{attained} = \frac{\sum_i P{\text{ME},i}^{\text{lim}} \cdot C_{f} \cdot \text{SFC} + P_\text{AE} \cdot C_{f,\text{AE}} \cdot \text{SFC}\text{AE}}{\text{Capacity} \cdot V\text{ref}^{\text{lim}}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{EEXI}_\text{attained}$ | Attained Energy Efficiency eXisting-ship Index | g CO₂ / (t·nm) | result |
| $P_{\text{ME},i}^{\text{lim}}$ | 75 % of limited MCR of main engine $i$ after EPL / ShaPoLi | kW | EPL / ShaPoLi declaration |
| $C_f$ | CO₂ conversion factor for main-engine fuel | t CO₂ / t fuel | MEPC.364(79) |
| $\text{SFC}$ | Main-engine specific fuel consumption at reference load | g / kWh | NOx Technical File |
| $P_\text{AE}$ | Auxiliary-engine power | kW | MEPC.231(65) §2.5.6 |
| $C_{f,\text{AE}}$ | CO₂ conversion factor for auxiliary-engine fuel | t CO₂ / t fuel | MEPC.364(79) |
| $\text{SFC}_\text{AE}$ | Auxiliary-engine specific fuel consumption | g / kWh | NOx Technical File |
| $Capacity$ | DWT (cargo) or GT (passenger / cruise) | t or - | MEPC.328(76) Table 1 |
| $V_\text{ref}^{\text{lim}}$ | Reference speed derived at 75 % of the limited power | kn | tank test / sea-trial |
Where the lim superscript denotes values AFTER engine or shaft power limitation.
Required EEXI
$$ \text{EEXI}\text{required} = \text{Reference} \cdot (1 - Z{\text{EEXI}}) $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{EEXI}_\text{required}$ | Required EEXI for the ship type and size band | g CO₂ / (t·nm) | result |
| Reference | EEDI reference line value $a \cdot \text{Capacity}^{-c}$ | g CO₂ / (t·nm) | MEPC.231(65) |
| $Z_{\text{EEXI}}$ | Ship-type reduction factor (see table below) | fraction | MEPC.328(76) |
| Ship type | Z |
|---|---|
| Bulk / tanker / gas / container | 20 % |
| General, refrigerated, PCTC | 15 % |
| Ro-Ro cargo, Ro-Pax | 5 % |
| LNG carrier, cruise | 30 % |
Limitation routes
- EPL (Engine Power Limitation) - physical limiter in the ME control system capping MCR. Removable by declaration for emergencies.
- ShaPoLi (Shaft Power Limitation) - instrumentation on the shaft that capsworked-power to the same effect.
Either lowers V_ref and thus reduces Attained EEXI proportionally to V_ref’s relationship with the cube of power.
Sources
- IMO MEPC.328(76) - revised MARPOL Annex VI including EEXI.
- IMO MEPC.364(79) - Cf conversion factors.