GHG Emissions Rating

GHG Emissions Rating Methodology

The core measure for comparing the relative efficiency of the world’s fleet is grams of CO2 per tonne nautical mile.

RightShip utilise one of two sources when determining an individual vessel’s efficiency:

  1. EEDI – which is a regulatory requirement for new ships developed by the IMO (and applied on an ad-hoc basis to existing vessels), or
  2. EVDI – developed by RightShip, the EVDI can be applied to existing vessels as well as new builds (where EEDI is not available/applicable).

As the two methods compare relative efficiency on the same basis, a like-for-like comparison of efficiency is achievable – as outlined in DNVGL’s review of RightShip’s methodology in 2015.

Source Data

RightShip recognises that the reliability of its calculations directly correlates to the accuracy of source data. RightShip continues to work closely with ship owners, managers, yards and classification societies to validate the data used for the calculations.

The source data for the GHG Emissions Rating is based on the following hierarchy:

Preference / Verification Level

Data Type

Data Source / Example

Most preferred /

Highest level of verification

Energy Efficiency Design Index

  • Classification Societies e.g. EEDI Technical Files


Ship specific specifications

  • Ship-sourced data, e.g. sea trial and shop test supplied by the vessel owner / manager


Industry / Third Party data sources

  • Engine manufacturer’s specifications.
  • Data sourced from Ship Yards

Least preferred /

Benefit from verification

IHS Maritime database

Industry publications

  • IMO publications
  • IHS Maritime Database

Specific fuel consumption figures are sourced from respective shop tests, or EEDI technical file, for each vessel.

If the data is not provided by the ship owner, the values used in the calculation are based on the same assumptions used in the IMO GHG Study and/or detailed in IMO Circulars on calculation of the energy efficiency measure as listed below.

Specific Fuel Consumption (Main Engine), SFCME 

Engine Age


SFCME (g/kWh)


> 15,000


5,000 to 15,000


< 5,000



> 15,000


5,000 to 15,000


< 5,000



> 15,000


5,000 to 15,000


< 5,000


Specific Fuel Consumption (Auxiliary Engine), SFCAE

Engine Age

MCRAE > 800 kW

MCRAE < 800 kW


220 g/kWh

230 g/kWh

The data utilised follows the same data set recognised by IMO MEPC in their establishment of the EEDI reference lines.  RightShip continue to refine and update the various assumptions which underpin the EVDI and are exploring improved SFC factors.

It should be noted, as outlined in the DNV GL review, due to data pre-defined set of assumptions applied to ‘non-verified’ vessels, there is an incentive for shipowners to update relevant data within Qi.

DNV GL methodology review

In January 2015 DNV GL commenced an independent methodology review of RightShip’s GHG Emissions Rating.

The review was finalised in November 2015 and the key points included:

  • There is a trend for the number of A-rated vessels to increase with younger vessel age. This observation, that there seems to be a correlation between year of build and A-G rating, and not only DWT, further strengthens the case of robustness for the scheme.
  • By analysing a sample dataset of over 10,000 bulk carriers, it was observed that the median difference of EVDI to EEDI was 5% (thereby EVDI being more conservative), which is enough to give an average improvement of A-G rating by over 1 rate, i.e. more than one A-G letter. 
  • There exists an incentive for interested parties (e.g. ship owners / managers) to update (‘verify’) EVDI values to remove any uncertainty that may exist between ‘verified’ and ‘non-verified’ ratings.

The executive summary of the outcomes of DNV GL’s methodology review can be found here.