EEXI vs EEDI: What Shipowners Need to Know
The International Maritime Organization (IMO) has strengthened its commitment to reducing greenhouse gas (GHG) emissions from shipping, which accounts for nearly 3% of global emissions. To meet the IMO’s Initial GHG Strategy—targeting a 40% reduction in carbon intensity by 2030 and a 50% reduction in total GHG emissions by 2050—mandatory regulations like the Energy Efficiency Design Index (EEDI) and the Energy Efficiency Existing Ship Index (EEXI) have been introduced.
Both regulations aim to improve ship energy efficiency and reduce CO₂ emissions, but they apply to different vessel categories and require distinct compliance strategies.
What is EEDI (Energy Efficiency Design Index)?
The EEDI ensures that newly built ships are designed with energy efficiency in mind. It has been mandatory for ships ≥400 GT under MARPOL Annex VI since January 1, 2013.
Applicability:
- New ships built after January 1, 2013
- Ships ≥ 400 GT, including container ships, bulk carriers, tankers, gas carriers, general cargo ships, and passenger vessels
Required and Attained Limits:
- Phase 0 (2013–2015): Baseline
- Phase 1 (2015–2020): 10% reduction
- Phase 2 (2020–2025): 20% reduction
- Phase 3 (2025 onward): Up to 30% reduction (depending on ship type)
✅ Think of EEDI as the “fuel efficiency rating” for new ships at the design stage.
What is EEXI (Energy Efficiency Existing Ship Index)?
The EEXI mirrors EEDI but targets the existing fleet. Introduced on January 1, 2023, it ensures older ships comply with IMO’s short-term GHG reduction strategy.
Applicability:
- Existing ships ≥400 GT built before EEDI regulations
- Part of IMO’s strategy to decarbonize the global fleet
Required and Attained Limits:
- Ships calculate attained EEXI and ensure it is ≤ required EEXI
- Reduction targets are comparable to EEDI Phase 2 or 3, depending on ship type and size
- Compliance often requires retrofits: Engine Power Limitation (EPL), hull/propeller upgrades, or installation of energy-saving devices
- One-time certification during the first IAPP survey after January 1, 2023
✅ Think of EEXI as a retroactive energy efficiency check-up for the existing fleet.
EEXI vs EEDI: Key Differences at a Glance
| Feature | EEDI (Energy Efficiency Design Index) | EEXI (Energy Efficiency Existing Ship Index) |
| Who it covers | Newly built ships (≥ Jan 1, 2013) | Existing ships built before EEDI regulations |
| Year Implemented | 2013 | 2023 |
| Focus | Design efficiency at construction | Retrofitting and modernization for efficiency |
| Calculation Basis | CO₂ per ton-nautical mile using design data | Same formula as EEDI, applied retrospectively |
| Compliance | Efficient design & technology | Retrofitting, EPL, operational measures |
How Diagnostic Tools Help Ships Comply
Accurate technical data is critical for calculating EEDI and EEXI. Tools such as Torsional Vibration and Torque Measurements and the Portable Marine Engine Diagnostic Device Collecting Three Different Signals play a central role in compliance verification and optimization.
Torsional Vibration and Torque Measurements (shaft torque and torsional vibration measurement systems)
- Real-time measurement of shaft torque, power, and torsional vibration
- Provides precise input data for attained index calculations
- Verifies the effectiveness of Engine Power Limitation (EPL)
- Detects propulsion inefficiencies such as misalignment or hull fouling
✅ Supports compliance verification and efficiency optimization
Portable Marine Engine Diagnostic Device Collecting Three Different Signals
- Analyzes engine combustion, condition, and vibration
- Ensures efficient engine operation, reducing fuel consumption and CO₂ emissions
- Detects issues such as injector faults or cylinder imbalance
- Provides before/after retrofit data to demonstrate improvements
✅ Enhances long-term compliance and energy efficiency
Combined Value:
- Verification & Compliance – Accurate data for IMO audits/class reports
- Optimization – Fine-tunes operations to reduce emissions
- Retrofit Justification – Demonstrates the effectiveness of upgrades and EPL
- Sustained Performance – Supports the Carbon Intensity Indicator (CII) beyond EEDI/EEXI
✅ Tools such as Torsional Vibration and Torque Measurements and the Portable Marine Engine Diagnostic Device Collecting Three Different Signals not only support compliance with regulations — they enable shipowners to measure, verify, and continuously optimize efficiency.