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Energy Efficiency Operational Indicator (EEOI)

It present the concept of an indicator for the energy efficiency of a ship

It can be used to establish a consistent approach for voluntary use of an EEOI as its not mandatory.

It will assist ship-owners/operators in the evaluation of the performance of their fleet with regard to CO2 emissions.

Ship-owners are invited to implement either these Guidelines or an equivalent method in their environmental management systems.

To provide assistance in the process of establishing a mechanism to achieve the limitation or reduction of greenhouse gas emissions from ships in operation.

It present the concept of an indicator for the energy efficiency of a ship in operation, as an expression of efficiency expressed in the form of CO2 emitted per unit of transport work.

These are intended to provide an example of a calculation method which could be used as an objective, performance-based approach to monitoring the efficiency of a ship’s operation.

When using the EEOI as a performance indicator, the indicator could provide a basis for consideration of both current performance and trends over time.

One approach could be to set internal performance criteria and targets based on the EEOI data.

In simple form,

Energy Efficiency Operational Indicator is defined as the ratio of mass of CO2 (M) emitted per unit of transport work:

Indicator = M
CO2/ (transport work)

In order to establish the EEOI, the following main steps will generally be needed:

  • define the period for which the EEOI is calculated
  • define data sources for data collection
  • collect data
  • convert data to appropriate format
  • calculate EEOI.
Primary data sources selected could be the ship’s log-book (bridge log-book, engine log-book, deck log-book and other official records).


Ideally, the data recording method used should be uniform so that information can be easily collated and analysed to facilitate the extraction of the required information. 

The collection of data from ships should include the distance travelled, the quantity and type of fuel used, and all fuel information that may affect the amount of carbon dioxide emitted.

It is important that sufficient information is collected on the ship with regard to fuel type and quantity, distance travelled and cargo type so that a realistic assessment can be generated.

The distance travelled should be calculated by actual distance travelled, as contained in the ship’s log-book.

Documented procedures to monitor and measure, on a regular basis, should be developed and maintained. Elements to be considered when establishing procedures for monitoring could

• identification of operations/activities with impact on the performance;

• identification of data sources and measurements that are necessary, and specification of the format;

• identification of frequency and personnel performing measurements; and

• maintenance of quality control procedures for verification procedures.

The results of this type of self-assessment could be reviewed and used as indicators of the System’s success and reliability, as well as identifying those areas in need of corrective action or improvement.

It is important that the source of figures established are properly recorded, the basis on which figures have been calculated and any decisions on difficult or grey areas of data. This will provide assistance on areas for improvement and be helpful for any later analysis.

In order to avoid unnecessary administrative burdens on ships’ staff, it is recommended that monitoring of an EEOI should be carried out by shore staff, utilizing data obtained from existing required records such as the official and engineering log-books and oil record books, etc.

The necessary data could be obtained during internal audits under the ISM Code, routine visits by superintendents, etc.

Calculation of EEOI
The basic expression for EEOI for a voyage is defined as:
               ∑ FCj * CFj
EEOI= ----------------------
cargo * D

Where average of the indicator for a period or for a number of voyages is obtained, the Indicator is calculated as:
                               ∑ ∑ (FCij * CFj)
                                i  j
Average EEOI = ------------------------------
                              ∑ (m
cargo, i * Di)

j- is the fuel type;
i- is the voyage number;
FCi j- is the mass of consumed fuel j at voyage i;
CFj- is the fuel mass to CO2 mass conversion factor for fuel j;
cargo- is cargo carried (tonnes) or work done (number of TEU or passengers) or gross tonnes for passenger ships; and
D- is the distance in nautical miles corresponding to the cargo carried or work done.

The unit of EEOI depends on the measurement of cargo carried or work done, e.g., tonnes CO2/(tonnes • nautical miles), tonnes CO2/(TEU • nautical miles), tonnes CO2/(person • nautical miles), etc.

Fuel mass to CO2 mass conversion factors (CF)
CF is a non-dimensional conversion factor between fuel consumption measured in g and CO2 emission also measured in g based on carbon content. 

The value of CF is as follows:

Type of fuel
1. Diesel/Gas Oil
ISO 8217 Grades DMX through DMC
2. Light Fuel Oil (LFO)
ISO 8217 Grades RMA through RMD
3. Heavy Fuel Oil
ISO 8217 Grades RME through RMK
4. Liquified Petroleum
Gas (LPG)
5. Liquified Natural Gas


Rolling average indicator
As a ship energy efficiency management tool, the rolling average indicator, when used, should be calculated by use of a methodology whereby the minimum period of time or a number of voyages that is statistically relevant is used as appropriate. 

“Statistically relevant” means that the period set as standard for each individual ship should remain constant and be wide enough so
the accumulated data mass reflects a reasonable mean value for operation of the ship in question over the selected period.

Calculation of the EEOI – Rolling average
EEOI is normally calculated for one voyage.
Average EEOI for a number of voyages can be carried out.
Rolling average, when used, can be calculated in a suitable time period, for example:

  • One year or 
  • Number of voyages, for example six or ten voyages. 
  • For calculation of rolling average for three voyages, the average for the following voyages need to be calculated: 
  • Average of voyages 1,2 and 3 will give the 1st rolling average 
  • Average of voyages 2, 3 and 4 will give the 2nd rolling average 
  • Average of voyages 3, 4 and 5 will give the 3rd rolling average 
  • And so on. 


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