For a ship subject to MARPOL Annex VI Regulation 25 (EEXI), Engine Power Limitation (EPL) under MEPC.335(76) or Shaft Power Limitation (ShaPoLi) under MEPC.357(78) is the standard compliance mechanism when technical or operational measures alone are insufficient. The required limited MCR is sized to bring the attained EEXI down to the Required EEXI for the ship type and size.
Required limited MCR
$$ \text{MCR}\text{limited} = \text{MCR}\text{original} \cdot \left(\frac{\text{EEXI}\text{required}}{\text{EEXI}\text{original}}\right)^{3/2} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{MCR}_\text{limited}$ | Required limited maximum continuous rating | kW | result |
| $\text{MCR}_\text{original}$ | Original installed MCR | kW | EIAPP Certificate |
| $\text{EEXI}_\text{required}$ | Required EEXI per MEPC.328(76) | g CO₂ / (t·nm) | reduction-factor table |
| $\text{EEXI}_\text{original}$ | Attained EEXI computed at the original MCR | g CO₂ / (t·nm) | EEXI formula |
The 3/2 exponent reflects the combined cubic speed-power relationship (P ∝ v³) and the linear power-CO₂ relationship at constant SFC. The attained EEXI scales as MCR^(2/3) at constant capacity, distance and Cf, hence inverting the relationship gives the 3/2 exponent.
Speed at limited MCR
$$ v_\text{limited} = v_\text{original} \cdot \left(\frac{\text{MCR}\text{limited}}{\text{MCR}\text{original}}\right)^{1/3} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $v_\text{original}$ | Reference design speed at 75% original MCR | knots | EEXI Technical File |
| $v_\text{limited}$ | Estimated maximum speed at limited MCR | knots | result |
Speed loss from the cubic-law approximation. For ships with hull forms optimised for a single design speed, the actual speed loss may be slightly larger than the cube-root estimate; verify with a sea trial under MEPC.366(79).
Constraints
- The limited MCR must remain at or above the Minimum Propulsion Power required by IMO MEPC.232(65). The MPP is calculated as a function of ship type, deadweight and applicable Beaufort scale.
- For ships using ShaPoLi, the alarm threshold is typically set 5% above the limited MCR to allow for measurement uncertainty and brief transients.
- The Onboard Management Manual (OMM) must specify the emergency unsealing procedure (for EPL) or the unlimited operation procedure (for ShaPoLi) and the operational scenarios in which it may be invoked.
Worked examples
| Ship | Original EEDI | Required EEXI | Original MCR (kW) | Limited MCR (kW) | Reduction | Speed loss |
|---|---|---|---|---|---|---|
| 50,000 DWT bulk carrier | 5.0 | 4.2 | 7,500 | 5,775 | 23% | 8% |
| 12,000 TEU container ship | 13.0 | 11.0 | 60,000 | 46,680 | 22% | 8% |
| LR1 product tanker | 7.5 | 6.0 | 12,500 | 8,944 | 28% | 11% |
| 80,000 DWT bulk carrier | 4.5 | 4.0 | 10,500 | 8,778 | 16% | 6% |
| 320,000 DWT VLCC | 2.0 | 1.8 | 27,000 | 23,030 | 15% | 5% |
Sources
- IMO Resolution MEPC.328(76) - Amendments to MARPOL Annex VI introducing EEXI under Regulation 25.
- IMO Resolution MEPC.335(76) - 2021 Guidelines on the Limitation of Maximum Engine Power for EEXI Compliance.
- IMO Resolution MEPC.357(78) - 2022 Guidelines for the Limitation of Maximum Power for ShaPoLi.
- IMO Resolution MEPC.366(79) - 2022 Guidelines on Sea Trial Verification.
- IMO Resolution MEPC.232(65) - 2013 Interim Guidelines for Determining Minimum Propulsion Power.
- IMO Resolution MEPC.364(79) - 2022 Guidelines on the Method of Calculation of the Attained EEXI.