How RightShip GHG’s Rating incorporates EEXI alongside EVDI and EEDI

RightShip’s GHG Rating is the industry’s first rating to incorporate EEXI, EVDI, and EEDI, and this change has necessitated a shift in how we define a vessel’s theoretical CO2 emissions.    

GHG Rating 1.0 rated a vessel based on engine power, using characteristics of the ship at build, like capacity, engine power, and fuel consumption. This is a strong methodology, but it doesn’t allow for the efficiency variables introduced by engine power limitation (EPL), which is expected to be adopted on a large proportion of the world fleet to comply with EEXI.  

GHG Rating 2.0 addresses this issue by moving to a speed corrected methodology. This approach evaluates all vessels within a peer group at a common speed and focuses on the emissions in the range of a vessel’s market operating speeds, applying a minimum speed logic for calculating the speed corrected intensity.    

In other words: the GHG Rating 1.0 graded vessels according to their efficiency at 75% of the engine power. Rating 2.0 grades vessels according to the efficiency at a common speed.  

This change ensures that the GHG Rating remains fair and transparent when considering EEXI and continues to function as an effective relative measure of efficiency between similar vessels.  

 

The Admiralty principle and EPL

The sea trial and associated speed-power performance data is obtained within the IMO framework and guidelines to arrive at a no wind, no wave, no sea current, depth and water temperature correction. However, there is a gap, as widely known and discussed with the market, wherein sea trials are completed at ballast draft conditions, as single or few point speed trial runs, which are then extrapolated to form the whole Speed-Power curve.

Considering the above limitations, a theoretical approach based on known design principles of Naval Architecture, specifically around the ‘Admiralty Coefficient’ - sometimes referred to as propeller law - is taken to arrive at a speed corrected gCO2/tnm.  

What is RightShip’s position on the Power Limitation (EPL/ShaPoli) for the EEXI Compliance, and how will this affect vessels’ GHG Rating?  

RightShip’s GHG Rating now accepts multiple EPL/ShaPoLi, and below MPP Level 1. The use of the Admiralty principle in the new speed corrected approach will remove the influence of EPL/ShaPoLi on a vessel’s rating. Class certified EEDI and EEXI Technical files are accepted.

 

GHG Rating and CII

The RightShip GHG Rating has moved to a 5-point A-E scale primarily due to the IMO’s adoption of an A-E scale for the Carbon Intensity Indicator (CII) rating. CII and GHG are fundamentally different – CII measures how a vessel actually performed in the past, while GHG Rating measures the designed potential to perform. A vessel’s CII does not impact its GHG Rating. However, we believe it’s important to give stakeholders the chance to understand these two ratings in relation to each other.  

For example: A vessel rated ‘A’ GHG gets chartered out for one year. It is returned to the vessel owner after one year, but it is CII rated ‘C’ due to the way it was traded. This CII rating, which may impact the vessel’s commercial viability, does not reflect the vessel’s potential or future performance. That’s what makes RightShip’s GHG Rating so important: it ensures that vessel’s are treated fairly, on a level playing field, and are measured according to their potential, not their past performance.