Operational Issues Complicate CO2 Formulas


By Wendy Laursen 2015-09-08 18:49:24

The IMO Energy Efficiency Operational Indicator (EEOI) has been examined using data from the Belgian Shipowners Association fleet with the study highlighting that market factors influence ship operations in a way that cascades into changes in the EEOI over time.

The University College of London (UCL) Energy Institute was commissioned by the Royal Belgian Shipowners Association (RBSA) to provide insights into CO2 emissions in preparation for the European Commission’s proposal to require ships exceeding 5,000 gross tons to monitor and report their operational energy efficiency starting in 2018 on all voyages to, from, and between E.U. ports. 

The EEOI was developed by the IMO in order to allow ships to monitor the carbon emissions of their shipping activities. The EEOI is the total carbon emissions in a given time period per unit of revenue ton-miles. 

Variations in the index are mainly caused by three factors: the technical efficiency of the ship, the amount of cargo transported per unit of time and variations in speed. However, as the EEOI is an aggregate number, it is difficult to identify the influence of these factors.

The study found significant differences in the laden EEOI (fuel consumption in ballast voyages and port excluded) when a ship was operated on the spot market compared to time charter, resulting in a higher laden EEOI for ships on time charter.

Fleet Data

UCL examined individual ship’s as well as fleets’ data over a five to six years timespan in order to provide an evidence-based opinion on the merits of different operational energy efficiency indices. The report also discusses the challenges for policymakers in implementing MRV given the uncertainty in the data and measures to sanitize the data for analysis.

A series of analyses were carried out on a set of owner-reported data, similar to the data that will be used to comply with the future legislation. As well as calculating the carbon emissions and values of EEOI for ships in the Belgian fleet, the study decomposed the EEOI into sub-indices looking at the contribution of the laden, ballast and port segments to the total EEOI for 94 ships in the bulk carrier, chemical tanker, container, LPG carrier and oil tanker sectors over the period 2008-2014, in which there was variation in market factors such as fuel prices and freight rates. 

Given the bleak prospects for the shipping industry at the end of 2008 (the first year of the study’s time period) and high fuel prices to 2013, all ships in the study were slow steaming until at least 2013 as the cost savings were more valuable than saving time. The payload utilization (actual mass of the cargo/DWT) also followed a similar declining trend in line with the deteriorating market conditions.  


The researchers concluded that technical and logistic factors are the key drivers of the EEOI. There is a correlation between the Energy Efficiency Design Index (EEDI) and the EEOI across different ship sizes, but there is a wide dispersion of EEOI values within a ship size class. This can be explained by the variation in logistic factors with little evidence of correlation between the EEOI and any single logistic factor. 

For all the types and sizes considered, variations in EEOI can be explained only by considering contributions from a combination of the logistic factors (including payload utilization and allocative utilization). 


For each of the different ship types and sizes, the alternative operational energy efficiency indices (currently being discussed at the IMO) show varying levels of agreement or disagreement. It was often the case that the three alternative indicators produced different trends to the EEOI. This shows that a) no alternative energy efficiency metric is a reliable proxy to EEOI and b) the choice of energy efficiency metric is a function of what information is believed to be of greatest importance. 

Of the indicators considered, the EEOI is the only indicator that represents the carbon intensity of the actual transport work done. All other indicators approximate transport work done in some way. 

The estimated trend in EETI (the EETI is a ship’s estimated technical efficiency in real operating conditions at a specific point in time) appears consistent with expectations that performance is likely to deteriorate over time (e.g. coating and fouling deterioration, propeller damage and engine wear). 

However, EEOI improvements are being obtained over the period of the study (reducing EEOI with time) in spite of this underlying technical efficiency deterioration, mainly due to extensive implementation of slow steaming.

Shipowners Preparing for Legislation

In light of the potential MRV legislation, shipowners and their associations are trying to better understand the drivers of the proposed EEOI in order to prepare themselves. The study aims to assist with those preparations.

Discussions at the IMO indicate that such monitoring, reporting and verification (MRV) initiatives could serve as initial phases toward eventual in-use ship fleet efficiency standards. Also, the collection of fuel consumption data, as required by the MRV policy, has led to speculation about how the EEOI could be extended to other regulations or for commercial purposes. 

One of the commonly cited barriers in the shipping industry, however, is the lack of sufficient information on the technical efficiency of a ship operated in real operating conditions when a ship is chartered. Although there is publicly available data that approximates the technical efficiency of a ship when it is built, the efficiency of a ship in its designed condition at age 0 does not necessarily equal the ship’s technical efficiency because the EEDI formula makes assumptions about parameters that determine efficiency. 

Furthermore, as a ship ages, the specific parameters that determine its fuel consumption change over time due to a gradual deterioration of the hull’s surface and fouling due to marine growth. For example, two ships which appear identical in their design characteristics can perform differently due to a difference in maintenance or retrofitting which would not be observed in the EEDI.

Although shipowners measure fuel consumption and cargo information, it is not known to what extent this data is used for improving operations. As a result, the industry lacks a detailed understanding of the consequence of energy efficiency interventions on its emissions.