Attributes ballast-leg fuel to the paired laden leg so the round-trip EEOI reflects real commercial performance.
Formula
$$ \text{EEOI}\text{rt} = \frac{(F\text{laden} + F_\text{ballast}) \cdot C_f \cdot 10^6}{m_\text{cargo} \cdot d_\text{laden}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{EEOI}_\text{rt}$ | Round-trip Energy Efficiency Operational Indicator | g CO₂ / (t cargo · nm) | result |
| $F_\text{laden}$ | Fuel burned on the laden leg | t | voyage log |
| $F_\text{ballast}$ | Fuel burned on the ballast leg | t | voyage log |
| $C_f$ | CO₂ conversion factor for the fuel | t CO₂ / t fuel | MEPC.364(79) |
| $m_\text{cargo}$ | Cargo mass delivered | t | bill of lading / cargo manifest |
| $d_\text{laden}$ | Distance of the laden leg | nm | voyage log |
| $10^6$ | Tonnes → grams | - | constant |
The ballast distance does NOT enter the denominator - ballast miles produce zero cargo-work. Per-leg AER hides this by treating every mile as equal regardless of cargo on board.
Sources
- IMO MEPC.1/Circ.684 - EEOI guidelines.
- IMO MEPC.364(79) - Cf factors.