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How to Calculate EEXI: Formula, Example, and Tools

As the shipping industry works toward decarbonization, the Energy Efficiency Existing Ship Index (EEXI) has emerged as a key regulation introduced by the International Maritime Organization (IMO) under MARPOL Annex VI. EEXI is a technical measure designed to assess the energy efficiency of existing ships by calculating their CO₂ emissions relative to their transport work capacity.
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Unlike the EEDI (Energy Efficiency Design Index), which applies to new vessels, EEXI was introduced to ensure that older ships also align with global emission standards. This index is part of the IMO’s Initial Strategy on the Reduction of Greenhouse Gas Emissions from Ships, which aims to reduce carbon intensity by at least 40% by 2030, compared to 2008 levels.

For shipowners and operators, understanding how to calculate the EEXI is crucial not only for regulatory compliance but also for operational planning and emissions reduction. In this blog, we will explain the EEXI formula, walk you through a sample calculation, and introduce tools that make EEXI calculations easier and more accurate.

Understanding the EEXI Formula

What is the EEXI Formula?

The Energy Efficiency Existing Ship Index (EEXI) is calculated using the following formula:
EEXI =
(Cf · PME · SFC · fi · fj) + (Cf · PAE · SFCAE)
Capacity · Vref

Key Component Definitions

Symbol Description
CO₂ conversion factor (Cx) Represents the CO₂ emissions per unit of fuel consumed. For Heavy Fuel Oil (HFO), it is typically 3.114 gCO₂/g fuel.
PME Installed power of the main engine (kW).
SFC Specific Fuel Consumption of the main engine (g/kWh).
fi Correction factor for specific design or technical features (e.g., ice-class notation).
fj Adjustment factor for innovative energy-saving technologies.
PAE Rated power of auxiliary engines (kW).
SFCAE Specific Fuel Consumption of auxiliary engines.
Capacity Usually Deadweight Tonnage (DWT) or Gross Tonnage (GT), depending on vessel type.
Vref Reference speed of the vessel under maximum power, typically measured in knots.
The goal is to compare the attained EEXI (from this calculation) with the required EEXI set by IMO based on ship type and size.

Step-by-Step Example of EEXI Calculation

Sample Calculation for a Bulk Carrier
Let’s consider a simplified example of a 50,000 DWT bulk carrier:
Given Data:
  • P_ME = 10,000 kW
  • SFC = 185 g/kWh
  • V_ref = 14 knots
  • Capacity = 50,000 DWT
  • C_f = 3.114 (for HFO)
  • fᵢ = 1 (no correction for ice-class)
  • fⱼ = 1 (no advanced technology installed)
  • P_AE = 1,000 kW
  • SFC_AE = 200 g/kWh

Step-by-Step Calculation

  • Numerator:
    (3.114⋅10,000⋅185⋅1⋅1)+(3.114⋅1,000⋅200)=5,760,900+622,800=6,383,700
  • Denominator:
    50,000⋅14=700,00050,000 \cdot 14 = 700,00050,000⋅14=700,000
  • Final EEXI Value:
EEXI =
6,383,700
700,000
= 9.12 gCO₂ / ton·nm
Let’s assume the required EEXI for this bulk carrier is 8.5 gCO₂/ton·nm. In this case, the ship does not comply and must take corrective action.

Correction and Conversion Factors

What are fᵢ and fⱼ in the Formula?

fᵢ – Correction Factor:
  • Applied when specific design elements affect performance
  • Common for:
    - Ice-class ships (higher resistance)
    - Ships with shaft generators or PTO (Power Take-Off)
fⱼ – Technology Adjustment Factor:
  • Used when energy-saving technologies are installed, such as:
    - Air lubrication systems
    - Wind-assisted propulsion
    - Waste heat recovery systems
These factors help ensure fairness in EEXI scoring by considering both handicaps and enhancements. They are detailed in IMO’s MEPC.333(76) guidelines and should be applied only when justified by technical documentation.

Required vs Attained EEXI

The required EEXI is defined by IMO for each ship type and size based on a reference line derived from the Energy Efficiency Design Index (EEDI) for new ships. It is generally:
RequiredEEXI = EEDIReferenceLine × (1 − ReductionFactor)
Example Reduction Factors (from MEPC.333(76)):
Ship Type DWT Required Reduction
Bulk Carrier ≥ 50,000 20%
Tanker ≥ 120,000 25%
Container Ship ≥ 200,000 50%
Each ship must achieve an attained EEXI ≤ required EEXI to be compliant.

Tools for Calculating EEXI

EEXI Calculation Tools and Software:
Recommended Tools:
  • IMO’s EEXI Calculator:
    Official spreadsheet-based calculator.
  • DNV’s EEXI Express:
    Online platform for fast EEXI assessments.
  • ABS and Lloyd’s Register Tools:
    Class society portals with automated EEXI evaluations.
  • In-house Excel Templates:
    Used by consultants and ship technical teams for tailored scenarios.
Several tools are available to streamline the EEXI calculation process:
Required Data Inputs:
  • Engine power and SFC
  • Fuel type and C_f
  • Reference speed (sea trial or model-based)
  • DWT/GT
  • Correction factors (fᵢ, fⱼ)
  • Any installed energy-saving tech
These tools reduce manual errors and provide a basis for preparing the EEXI Technical File required by classification societies.

What to Do If Your Ship Fails EEXI

If a ship’s attained EEXI exceeds the required EEXI, corrective actions must be taken. These can include:
Compliance Strategies:
Engine Power Limitation (EPL):
  • Reduces the ship’s maximum engine output to lower emissions.
  • Simple, quick, and cost-effective solution.
  • Implemented by adjusting the engine control system and verified via EPL documentation.
  • Implemented by adjusting the engine control system and verified via EPL documentation.
Shaft Power Limitation (ShaPoLi):
  • Limits the maximum shaft power transmitted from the engine to the propeller.
Propulsion System Optimization:
  • Retrofit or upgrade components such as propellers, rudders, or ducts.
Energy Efficiency Retrofits:
  • Introduce innovative technologies like:
    - Shaft generators
    - Low-friction hull coatings
    - Air lubrication systems
    - Waste heat recovery units
  • These solutions enhance fuel economy and reduce CO₂ emissions
Technical File Submission:
Each compliant vessel must submit an EEXI Technical File to its classification society. This document includes:
  • Detailed calculation
  • Sea trial reports or model test data
  • Description of applied correction factors or limitations
  • EPL documentation, if applicable

Conclusion

As the maritime industry navigates stricter environmental regulations, mastering the EEXI calculation is essential for shipowners and operators. Not only is it a compliance requirement, but it also serves as a benchmark for evaluating a ship’s operational efficiency.

With the right tools, accurate data, and a proactive approach to retrofitting, achieving EEXI compliance can be straightforward and beneficial in the long term. Don’t wait until inspections or penalties become an issue—calculate your EEXI early, identify gaps, and plan smart.

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