Generally sister ships will have the same, or similar, GHG Emissions Rating as they are ‘nearly identical’ in terms of build and specifications.
However when the relative efficiency is assessed several factors can influence the GHG Rating including:
- Verification status– if a vessel’s specifications have been updated by the shipowner the GHG Rating may be superior to ‘unverified’ sister ships. As DNV GL noted in their 2015 review, there is an incentive for shipowners to verify vessel specifications to ensure the data is up to date and accurate.
- Changes in specifications – sister ships can be built over a number of years and changes including DWT, engine type, and materials used are not uncommon.Small changes in specifications between sister ships can sometimes impact the relative efficiency and subsequent GHG rating of a vessel.
- Distribution of peer group – the GHG Rating is a comparison of ships of the same size and type. As such, the distribution of the peer ships will impact on the respective GHG Ratings. For example, a peer group may be made up of predominantly new ships, as is the case for some LNG tanker peer groups, and therefore ships which are only a few years old may attain an average or poor rating.