RightShip GHG Rating: the vessel efficiency letter

RightShip GHG Rating is a commercial A-to-E letter published per vessel by RightShip, an Australian company founded in Melbourne in 2001, grading a ship’s design carbon intensity against the mean of a peer group of similar ships. It carries no statutory force. It rests on the Existing Vessel Design Index , a theoretical figure in grams of CO2 per tonne-nautical-mile, and charterers, terminals and cargo owners use it to screen tonnage before fixture.

The scale changed on 6 December 2023. RightShip retired the seven-band A-to-G scale and replaced it with a five-band A-to-E scale, stating the change was made primarily because the IMO had adopted an A-to-E scale for the Carbon Intensity Indicator . Any clause, broker report or fixture recap quoting an A-to-G letter describes the earlier scheme, and the migration was not symmetrical: old A and old B both became new A, and old F and old G both became new E.

What the RightShip GHG Rating is

The rating is one letter, A through E, attached to a named ship, expressing how carbon-efficient that ship’s design is relative to ships of the same type within plus or minus 10 percent of its deadweight. A is the most efficient band, E the least, and C is the wide middle band holding roughly 36 percent of a peer distribution. The letter is a ranking, not a threshold.

Under the current methodology the letter is derived from a size score: the number of standard deviations a ship’s index value sits from its peer-group mean, sign-reversed so a positive score reads as better than average. This matters more than it sounds. A ship can hold its index value unchanged and still lose a band, because the peer mean improves beneath it as older tonnage is scrapped and newer tonnage delivers.

The index feeding the score is not always the EVDI. Since GHG Rating 2.0 the rating accepts class-certified attained EEDI and EEXI Technical Files, and EEXI overrides the EVDI for existing ships. So the rating draws on three indices in precedence order, and the EVDI is the fallback for tonnage that has neither of the regulatory figures.

A design index measures potential. It states how efficient a hull, engine and propeller combination should be at a defined speed and loading, and it says nothing about whether the ship ran fouled, idled at anchor, or steamed above its design point. That gap is the single most important thing to understand about the letter, and it is why RightShip states plainly that a vessel’s CII does not affect its GHG Rating.

Who publishes the rating, and who owns RightShip

RightShip is an Australian company, founded in Melbourne in 2001 as a two-party joint venture between BHP Billiton and Rio Tinto. Its published offices are Melbourne, London, Singapore, Sugar Land in Texas, Gozo in Malta and Hanoi. Its chief executive is based in Singapore, and its September 2025 ownership announcement carried a Singapore dateline.

Cargill was not a founding party. It acquired a one-third interest later, the shares coming in equal portions from the two founding partners, as reported by trade press in September 2006. RightShip’s current corporate material describes all three as founding shareholders, which reflects the present ownership rather than the 2001 formation.

BHP, Cargill and Rio Tinto each hold equal stakes today. On 4 September 2025 RightShip announced that funds advised by Permira had agreed to acquire a strategic minority stake, with the three existing shareholders each retaining equal stakes. The announcement stated the transaction was subject to customary regulatory approvals, and no transaction value was disclosed.

The company’s own account of its origin runs to the Australian bulk carrier casualty record. RightShip states that nearly 100 seafarers were lost on large bulk carriers between 1988 and 1991, mostly off the coast of Western Australia, and both founders shared a common Capesize risk pool out of those ports. Founding chief executive Warwick Norman framed the design intent as rating the performance of the actors in the safety chain, meaning classification societies , flag states , owners, managers and shipyards, rather than adding another inspection layer.

When the rating actually started

RightShip’s corporate timeline dates the development of the Greenhouse Gas Emissions Rating to 2009. The earliest published first-party methodology report is dated 4 June 2010. RightShip dates the EVDI itself to 2012, and elsewhere dates the rating’s public service from 2012.

The free public lookup, ShippingEfficiency.org, was a joint initiative with the Carbon War Room from around 2010. That partnership is why the rating borrowed the European A-to-G domestic energy-label scale in the first place, a lineage worth knowing because it explains a band structure that never had a regulatory logic behind it. Carbon War Room merged into RMI in 2014.

The rest of the platform grew around the rating: the Houston office in 2005, London in 2007, the RightShip Qi platform in 2016, the current Platform and the Safety Score in 2021, the acquisition of Thynk Software’s maritime technology business in 2022, RightSTORE and GHG Rating 2.0 in 2023, and the Dry Bulk Centre of Excellence with INTERCARGO in 2024.

How the index is calculated

The index is the IMO attained-EEDI equation, applied to ships that have no regulatory EEDI and populated from a ranked fallback data hierarchy. This is the correction that matters most to anyone reading the older literature, which commonly describes the EVDI as a separate index that merely “mirrors” the EEDI. It does not mirror it. RightShip publishes the same numerator and denominator, and states its data is, as far as practicable, in line with the IMO guidelines for EEDI calculation.

The numerator is the rate at which the ship emits CO2 at its evaluation point, summing main engine, auxiliary engine and shaft-motor terms and subtracting the credit for approved energy-saving devices . The denominator is the transport work it does in the same conditions: capacity, a set of correction factors and the reference speed. The carbon conversion factor turns fuel mass into CO2 mass, and the specific fuel oil consumption comes from engine certification where a certificate exists. Capacity is deadweight for cargo ships and gross tonnage for passenger types, which is the same split the EEDI uses and the reason deadweight and lightweight have to be kept distinct when reading a rating.

The data source hierarchy, and what an unverified rating means

RightShip publishes a ranked source hierarchy for the inputs, from most to least preferred:

1. Energy Efficiency Design Index data from classification societies: EEDI Technical Files, and the EEDI certificate including its supplement.
2. Ship-specific specifications supplied by the owner or manager: sea trial and shop test results.
3. Industry and third-party data: engine maker specifications and shipyard data.
4. The IHS Maritime database, IMO publications and industry publications.

Where the owner has substantiated nothing, the rating falls to the bottom of that list. RightShip states an unverified rating rests on vessel-specific IHS inputs, IMO assumptions and sister-vessel data, so it is an indication built from proxies rather than from measured values. The platform displays whether a rating has been verified by the shipowner, and owners are notified where an unverified rating affects a vetting outcome.

That distinction has a measured cost. DNV GL’s 2015 review of the methodology replicated the rating on over 10,000 vessels from RightShip’s own vessel database and reported a median difference of about 5 percent between EVDI and attained EEDI for a bulk carrier sample, with the EVDI the more conservative figure. A 5 percent conservatism is enough to move a letter by more than one band, which is the entire commercial incentive to verify.

The speed-corrected method introduced in GHG Rating 2.0

Since 6 December 2023 the rating evaluates every ship in a peer group at a common speed rather than at a fixed fraction of installed power. RightShip states the common speed is referenced from the Fourth IMO GHG Study 2020, with a 10 percent reduction applied to allow for the slowdown of the world fleet attributable to EEXI and power limitation.

The reason is a distortion the earlier method could not absorb. GHG Rating 1.0 graded vessels at 75 percent of engine power, the same load point the EEDI uses. Once thousands of ships fitted an engine power limitation or shaft power limitation to meet EEXI, a de-rated ship burned less at its new rated power and looked cleaner on a power basis without being a better ship. RightShip has acknowledged that this could have led to artificial distortions which incentivised some inefficient vessels while discriminating against others.

The correction is derived from the Admiralty coefficient , the propeller-law relation, because sea trials are run at ballast draft over one or a few points and have to be extrapolated across the whole speed-power curve . RightShip’s stated policy is that EPL and ShaPoLi are operational measures rather than design measures, on the ground that they can be overridden, so the Admiralty principle is applied specifically to remove their effect. The practical consequence for an owner is blunt: fitting a power limitation to meet EEXI does not buy a better GHG letter. It was never intended to, and since 2.0 it mechanically cannot.

The cubic relationship between speed and power is what makes a common-speed comparison meaningful in the first place, and also what makes the 10 percent reduction a judgment rather than a measurement. RightShip has not published the sensitivity of the letter to that assumption.

From index to letter: the size score and its bands

The letter is a position in a peer distribution, expressed in standard deviations, and the band edges are fixed. RightShip’s published key sets A above a size score of 1.0, B above 0.5, C above minus 0.5, D above minus 1.0, and E below minus 1.0, corresponding to roughly 16, 16, 36, 16 and 16 percent of the peer population.

Source: RightShip, GHG Rating methodology, current at 2 September 2026.

The size score is a z-score. RightShip’s 2010 technical report defines it as the difference between the ship’s index value and the peer mean, divided by the peer standard deviation, computed on natural-log-transformed index values, and then sign-reversed. The report states the reason for the sign reversal directly: because low index values represent better energy efficiency, assigning a positive value to the score better represents good performance. Whether GHG Rating 2.0 retains the log transform is not published, and this article does not assume it does.

Two consequences follow from a peer-relative construction, and practitioners hit both.

The letter is not an absolute emissions statement. A ship rated A is in the best sixth of its peer group at its size and type. It is not below any particular carbon-intensity number, and an A-rated Capesize emits far more CO2 per voyage than an E-rated handysize. Comparisons only mean anything inside a peer group, which is why the bulk carrier size classes and tanker size classes matter to reading a letter.

The letter moves when the fleet moves. RightShip states the rating is dynamic and will almost always compare a different group of vessels at each calculation, and that it is common for a vessel’s size score and rating to change slowly over time. There is no published re-basing schedule and no trajectory anchor. The band edges stay at plus and minus 0.5 and 1.0; the distribution slides underneath them.

The retired A-to-G scale, and the December 2023 migration

The pre-December 2023 key ran to seven bands on a wider spread of standard deviations: A above 2.0, B above 1.0, C above 0.5, D above minus 0.5, E above minus 1.0, F above minus 2.0 and G at or below minus 2.0, with the extreme bands each holding about 2.5 percent of the distribution.

RightShip published the migration as a conversion: old A and old B become new A, old C becomes new B, old D becomes new C, old E becomes new D, and old F and old G become new E. The two keys are arithmetically consistent with each other, which is a useful check on the published mapping rather than a separate claim.

The asymmetry is the part that bites in contract. A vessel that held a C under the old scale holds a B under the current one, so a clause drafted to accept an old C is not satisfied by a current C. At the other end, a ship that was an F and a ship that was a G are now indistinguishable at E.

Legal status: a private benchmark, not a regulation

The rating carries no statutory force in any jurisdiction. No flag state, port state or classification society requires a letter, and no letter satisfies any obligation under MARPOL Annex VI or any other annex of the MARPOL Convention . A ship rated E can be fully compliant with every energy-efficiency regulation the IMO has adopted, and a ship rated A gains nothing in law by holding the letter.

What the rating has instead is concentration of cargo demand. A small number of miners, traders and energy companies control an outsized share of long-haul dry bulk and tanker demand, and where they screen on one benchmark, the benchmark becomes a commercial gate without ever becoming a legal one. That is a real mechanism and it is worth stating precisely, because it is also the limit: a charterer is free to ignore the letter, and nothing compels a fixture either way.

The contrast with the CII is exact. The CII sits in MARPOL Annex VI through MEPC.328(76) , adopted 17 June 2021 and in force 1 November 2022, and binds every flag and port state party to the convention. Its rating boundaries are published in an IMO resolution. The GHG Rating’s band edges are published by a company, on a page it can revise.

The rating against the IMO indices

The GHG Rating and the IMO indices answer different questions on different data, and conflating them is the most common error in commercial correspondence about the letter. The IMO carries two design measures and one operational measure. The GHG Rating reads the design measures and explicitly excludes the operational one.

EEDI: the design index for new ships

The Energy Efficiency Design Index was introduced by MEPC.203(62), adopted 15 July 2011, which inserted a new Chapter 4 into MARPOL Annex VI and entered into force on 1 January 2013. It applies to ships contracted on or after that date and is calculated once, at the design stage, against a required value that tightens in phases.

The reduction factors were replaced wholesale by MEPC.324(75), adopted 20 November 2020 and in force 1 April 2022. Two features of the current table are routinely misstated:

• Phase 3 does not have one start date. It began on 1 April 2022 for gas carriers of 15,000 DWT and above, container ships, general cargo ships of 15,000 DWT and above, LNG carriers, ro-ro cargo ships including vehicle carriers, ro-ro passenger ships and cruise passenger ships with non-conventional propulsion. It began on 1 January 2025 for bulk carriers, tankers, gas carriers below 15,000 DWT, refrigerated cargo carriers and combination carriers.
• Container ships are the only type whose Phase 3 factor exceeds 30 percent, and it is graded by size: 30 percent from 15,000 DWT, 35 percent from 40,000 DWT, 40 percent from 80,000 DWT, 45 percent from 120,000 DWT and 50 percent at 200,000 DWT and above.

Note also that the regulation numbering moved. Under MEPC.203(62) the required EEDI sat at regulation 21. Under the 2021 Revised Annex VI the attained EEDI is regulation 22, the attained EEXI regulation 23, the required EEDI regulation 24 and the required EEXI regulation 25. A citation to “regulation 21” for the required EEDI is citing superseded numbering.

The calculation guidelines have moved three times. MEPC.364(79), adopted at MEPC 79 in December 2022, supersedes the 2018 guidelines in MEPC.308(73) as amended by MEPC.322(74) and MEPC.332(76), which in turn superseded MEPC.245(66). Survey and certification is MEPC.365(79). RightShip’s own published methodology still anchors to MEPC.245(66), which is a fact about RightShip’s documentation rather than an error to correct in it.

EEXI: the design index applied to existing ships

The Energy Efficiency Existing Ship Index was introduced by MEPC.328(76), adopted 17 June 2021, deemed accepted 1 May 2022 and in force 1 November 2022. It applies to ships of 400 GT and above, a different threshold from the CII, and is verified at the first annual, intermediate or renewal survey, whichever falls first, on or after 1 January 2023. It is a once-in-a-lifetime attainment rather than a recurring one.

Calculation guidelines are MEPC.350(78), adopted 10 June 2022, which revoked MEPC.333(76); survey and certification is MEPC.351(78), which revoked MEPC.334(76). The power-limitation route is MEPC.335(76), adopted 17 June 2021, current as amended by MEPC.375(80) of 7 July 2023 and MEPC.390(81) of 22 March 2024.

EEXI is where the GHG Rating and the regulation touch most directly, and in two opposite ways. A class-certified EEXI Technical File is accepted as a rating input and overrides the EVDI. The power limitation used to achieve that EEXI is stripped out of the rating by the Admiralty correction.

CII: the operational grade, and why it does not feed the rating

The Carbon Intensity Indicator applies to ships of 5,000 GT and above in twelve named categories under regulation 28, not to ships of 400 GT and above. It is computed from a ship’s actual annual fuel burn and distance sailed, reported under the IMO Data Collection System , and compared to a required value to yield an A-to-E letter.

The current guideline chain is not the 2021 set commonly cited. G1 is MEPC.352(78) as amended by MEPC.412(84) of 1 May 2026, G2 is MEPC.353(78), G3 is MEPC.338(76) as amended by MEPC.400(83) of 11 April 2025, G4 is MEPC.354(78), and the interim G5 is MEPC.355(78). MEPC.336(76), MEPC.337(76) and MEPC.339(76) were all revoked on 10 June 2022. The reference year is 2019, not 2008. The supply-based indicator using deadweight is the Annual Efficiency Ratio ; the one using gross tonnage is cgDIST.

RightShip’s position on the relationship could not be more direct. It states there is no relationship between a vessel’s CII and its GHG Rating, and that a vessel’s CII does not impact its GHG Rating. Since 5 June 2024 the platform displays a vessel’s annual and estimated CII alongside the letter, on the same A-to-E colour coding, but RightShip states those figures are for insight only and are not used in its vetting rules or baseline criteria. Asked directly whether the annual CII rating would be used in its vetting rules, RightShip answered no, on the stated ground that CII in its current structure is not suitable for vessel selection through those rules.

Where the EVDI and the IMO indices actually differ

Four differences, and only one of them is the formula.

Source: IMO MEPC.364(79) and MEPC.350(78); RightShip GHG Rating methodology, current at 2 September 2026.

The fifth difference is the one practitioners ask about most, and it belongs on its own line. Neither the EVDI nor the GHG Rating has any relationship to the CII. The ship efficiency indices hub sets all of them side by side.

Which ships are rated, and how many

RightShip rates commercial cargo tonnage across eleven type categories: bulk carriers, chemical tankers, container ships, crude and product tankers, passenger and cruise ships, general cargo ships, LNG carriers, LPG tankers, refrigerated cargo ships, ro-ro vessels and vehicle carriers. The categories predominantly follow those in MARPOL Annex VI as revised in 2021, regrouped by cargo type.

RightShip does not publish a current count of rated vessels. The figures it does publish measure different things and should not be read as coverage of the rating: more than 1,000 organisations use RightShip, and in November 2020 it stated it vets over 40,000 vessels annually. The only sourced coverage figure attached to the rating itself is historical, from DNV GL’s 2015 methodology review, which used over 10,000 vessels from RightShip’s vessel database.

Depth of coverage is uneven by segment, and the reason is historical rather than technical. The founding shareholders are dry bulk cargo buyers, and the rating grew up in the bulk carrier and oil tanker trades where they charter. Container ship coverage came later, and the chemical tanker and LNG carrier segments carry their own vetting regimes that a charterer weighs alongside the letter.

Verification, the plus suffix and dispute

Verification is what moves a rating off proxy data, and the owner initiates it. Through RightShip’s environmental review flow the owner submits an EEDI, EVDI or EEXI Technical File together with the International Energy Efficiency Certificate. A full EEDI or EVDI Technical File is preferred; failing that, RightShip accepts a capacity plan, shop tests, a sea trial report and other certified documents. Where an item is missing, RightShip raises a request for information that stays open for 30 days.

Review is carried out by RightShip’s own Sustainability team. There is no independent auditor and no appeal to a regulator. An owner contesting a letter is asking the publisher of the rating to reconsider its own rating, which is a materially different position from an appeal against a class decision or a port state control detention, where an external body and a published procedure exist.

A verified retrofit earns recognition in the letter. Modifications to propulsion, machinery or design, and approved energy-saving devices , can be submitted with classification-society verification and a new EEXI certificate to trigger recalculation. Approved measures earn a plus sign appended to the rating, and the devices are listed on the vessel’s platform profile. RightShip’s published example is Odfjell SE reaching A+ after a MAN Kappel propeller upgrade.

Coating claims carry their own evidence requirement, and it is specific enough to plan a docking around. The owner supplies the reference speed at 75 percent nameplate maximum continuous rating both with and without the paint improvement effect, the average hull roughness, and the surface-preparation standard, with the EVDI Technical File approved by an IACS member society or another class-approved methodology. That is a higher evidential bar than most owners expect from a commercial rating, and it is the reason a coating upgrade often fails to register.

Who uses the rating, and how it enters a vetting decision

Cargo buyers, terminals and ship-finance institutions use the letter as a screen before commitment, but the letter is not itself the gate. The gate is the vetting recommendation, a binary output of acceptable or unacceptable for a nominated voyage, produced by applying RightShip’s own standard plus any customer-specific criteria including berth fit.

RightShip’s own vetting standard

The clearest published threshold belongs to RightShip, not to any charterer. In the vetting criteria published on 17 November 2020, the criteria split into two kinds:

Source: RightShip, Introducing RightShip’s new vessel vetting criteria, 17 November 2020.

Two things follow. A binary failure means the vessel cannot be recommended at all. The GHG Rating is not binary: where a vessel falls below the criterion, the customer must confirm willingness to proceed and a due diligence time stamp is recorded. The compliance artefact is the recorded decision, not an exclusion. The letter named in that release is on the retired A-to-G scale, and RightShip has not republished its current equivalent, so this article does not state one.

Charterers may tighten the standard but not loosen it. RightShip’s worked example is a charterer capping vessel age at 25 years against RightShip’s own 35. A charterer can require a better letter than RightShip requires; it cannot instruct RightShip to recommend a vessel that fails a binary criterion.

No major charterer publishes a minimum letter that could be verified. RightShip states charterers can set a minimum GHG Rating within their chartering programme and filter and track against it, which describes a capability rather than any named company’s policy. Company-and-letter pairings quoted in secondary sources should be treated as unsourced unless the company itself has published them.

The GHG letter beside the Safety Score

RightShip publishes a separate Safety Score, launched with the Platform in 2021, replacing the earlier star rating and Qi risk rating. It is a score out of five built from a vessel’s incident record, its deficiency and port state control history and its class and flag performance, benchmarked against the historical operational performance of the world fleet. On 20 August 2025 RightShip changed the method so that PSC deficiencies are weighted by severity rather than counted against a regional average.

The two scores are not two floors in a single policy, and the relationship runs in one direction: RightShip states the vetting standard inspired the Safety Score rules rather than the reverse. In a fixture the practical sequence is that the safety and berth-fit assessment decides whether the vessel can be recommended, and the GHG letter conditions how the customer records its decision.

Terminals, ports and the incentive schemes

Terminals do use RightShip as a berth-nomination gatekeeper, but on the safety and berth-fit recommendation rather than the carbon letter. Terminal Questionnaires, administered by the terminal and facilitated by RightShip, cover mooring configuration, loading and deballasting rates and helicopter suitability, and post-call feedback reports feed the vessel’s operational history for future vets at that terminal. Published terminal rules that name RightShip describe it as the third-party vetting agent and limit its remit to berth fit.

No port authority prices its dues off the RightShip GHG letter. RightShip’s own published port evidence is incentive programmes: the Prince Rupert Port Authority Green Wave programme, running since 2014, and the Port of Quebec. The instruments that actually drive port-dues discounts at scale are different schemes:

• The Environmental Ship Index, a NOx and SOx formula administered by the Green Award Foundation, recognised by the IMO as a basis for port incentives, with a Port of Rotterdam discount on seaport dues.
• Green Award certification, which the Port of Rotterdam rewards with a 70 percent discount on the sustainability component of seaport dues for qualifying LNG, chemical, gas and oil or product tankers.

Conflating the two families is a common error, and it matters commercially: an owner chasing a port-dues rebate is chasing the wrong scheme if it is optimising a GHG letter.

The rating in the charter party

There is no BIMCO clause adopting the RightShip GHG Rating, and BIMCO’s published position runs against period RightShip warranties. The Dry Bulk Marine Risk Assessment Clause for Time Charter Parties 2013 was drafted to discourage provisions such as a requirement that the vessel shall be RightShip approved throughout the charter period.

BIMCO’s stated reasoning is factual rather than political: RightShip does not issue and has never issued period approvals. Its system produces a snapshot recommendation for a particular voyage from the data held at that moment, and a vessel’s status may shift at short notice through factors outside the owner’s control. BIMCO identifies the worst case as a charterer using a status change as a pretext to terminate.

The clause architecture allocates the risk accordingly:

• Charterers may conduct a marine risk assessment at their own time, risk, cost and expense, and owners give no warranty or representation that the vessel is or will be acceptable or recommended.
• Owners assist by submitting documentation in their possession and readily available, with no obligation to disclose confidential information.
• There is no automatic right of physical inspection: it requires particular grounds specified to owners, advance notice, an inspection checklist, owners’ approval not to be unreasonably withheld, and a mutually agreed time and place.
• Owners’ duty to act on recommendations is confined to what is consistent with and does not exceed existing charter party obligations, with class and flag requirements prevailing.
• The assessment process gives charterers no route to place the ship off hire.

What the English court decided

In Seagate Shipping Ltd v Glencore International AG (The Silver Constellation) [2008] EWHC 1904 (Comm), David Steel J held that there was no obligation on owners to obtain RightShip approval. The charter was on the NYPE 1946 form with an additional clause 31 on certificates, laws and regulations, and the court held those documentary provisions were confined to documents imposed by the law of the flag or of the country of call. RightShip approval formed no part of them, and the court accepted that approval was obtained voyage by voyage depending on the requirements of the shipper or loading terminal.

The obligation that does survive is separate and narrower. Under clause 8 of the NYPE form an owner is obliged to permit a RightShip inspection and other RightShip vetting procedures as and when required by the charterer. Permitting the process and warranting its outcome are different obligations, and the case is the authority for keeping them apart.

The practical rule for a chartering desk is that a charterer who wants a RightShip outcome must make it an express term, in the same way oil-major approval is made express in tanker charters. Steel J’s account of the nature of RightShip and its rating was later cited in Gemini Ocean Shipping Co Ltd v DHL Project and Chartering Ltd [2022] EWHC 181 (Comm).

Drafting a GHG warranty that an owner can actually perform

Market wording recorded by P and I clubs is a clause under which the owner guarantees a minimum RightShip GHG rating at the time of fixing or at delivery, rather than throughout the charter period. That temporal limitation is the drafting lesson, and it follows directly from BIMCO’s 2013 reasoning: a letter is a snapshot that can move through peer-group effects the owner does not control, so a continuing warranty transfers a risk the owner cannot manage.

The scale change adds a second check on any subsisting charter. A clause written before 6 December 2023 requiring a minimum C was written against a scale on which C sat above a size score of 0.5 and old C migrated to new B. A current C is a weaker vessel than that clause contemplated. Long-period charters and contracts of affreightment carrying a RightShip GHG warranty should be read against the methodology version in force when they were drafted, in the same way a speed and consumption warranty is read against the description it was given.

The BIMCO clauses that do bear on emissions in a time charter address the regulation rather than the rating: the EEXI Transition Clause of December 2021, the ETS Allowances Clause of May 2022, and the CII Operations Clause 2022 published in November 2022, under which the parties agree a CII to be achieved each year and must review and reset against new IMO annual targets where the charter runs past 31 December 2026.

How an owner improves a rating

Change an input the index reads, and get it verified. That sentence rules out most of what owners try first, because the GHG Rating is a design index and the majority of available efficiency levers are operational.

The routes that work are the ones RightShip publishes:

• Verify an unverified rating. The proxy data behind an unverified letter is conservative by a measured margin, so submitting a Technical File can recover a band the ship already deserved. This is the cheapest lever available and the one most often left unused.
• A class-verified retrofit or upgrade, submitted with a new EEXI certificate, covering propulsion, machinery or design changes.
• An approved energy-saving device, which earns the plus suffix and appears on the vessel’s platform profile. Air lubrication , wind-assisted propulsion and bulbous bow retrofits are the device families in common use.
• A low-friction coating, on the specific evidence set described above.
• A fuel change that lowers the carbon conversion factor, since the factor sits in the numerator. LNG , methanol , ammonia and biofuels each carry a different factor, and the well-to-wake accounting boundary determines how much credit a pathway attracts under any given scheme.

What does not work, and why owners keep trying it

An engine power limitation does not improve the letter. It is the single most common misconception, and it was true under GHG Rating 1.0 and false since 6 December 2023. The Admiralty correction in the speed-corrected method exists to remove exactly that effect. An owner fitting an EPL to meet EEXI is buying EEXI compliance, not a band.

Operational measures do not improve the letter either. Hull and propeller cleaning , trim optimisation , weather routing , just-in-time arrival and slow steaming all move the operational carbon intensity and the Annual Efficiency Ratio . They do not move a design index. An owner who cleans a hull should expect the CII to respond at the next annual submission and the GHG letter not to respond at all.

That split is not a defect to be worked around. It is the deliberate division of labour between the two metrics, and a vetting desk that reads only one of them is working with half the picture. The SEEMP and the CII corrective action plan sit on the operational side; the Technical File sits on the design side.

The disclosure frameworks, and what RightShip actually does for them

Neither the Poseidon Principles nor the Sea Cargo Charter uses the GHG Rating as an input. Both are portfolio-level, annual, AER-based disclosure frameworks computed from IMO Data Collection System data, and the GHG Rating is a vessel-level design metric that excludes operational performance. They are methodologically opposed rather than complementary, and the claim that banks use the letter to validate a portfolio alignment score is unsupported on both sides.

The Poseidon Principles launched on 18 June 2019 in New York with 11 founding banks holding over USD 100 billion in shipping assets. Principle 1, on assessment, mandates reliance on IMO standards and IMO-recognised organisations, and specifically on fuel oil consumption data reported under the IMO DCS. The association lists 36 signatories, and its sixth Annual Disclosure Report, published in November 2025, covered 35. Current Technical Guidance is version 5.2, and signatories report to the secretariat annually no later than 15 November.

The Sea Cargo Charter launched on 7 October 2020 and applies the same pattern to chartering activity rather than loan books. Its fifth Annual Disclosure Report, released 11 June 2026, covered 32 charterers, shipowners and operators representing about 14 percent of global seaborne trade, on average 11.6 percent behind the IMO minimum trajectory against 12.2 percent the year before. Of 29 repeat reporters, 20 reduced emission intensity in 2025.

A third scheme, the Poseidon Principles for Marine Insurance, launched in December 2021 for hull and machinery portfolios and entered into force on 27 April 2022 once its ninth signatory joined.

RightShip’s real connection to this layer is commercial rather than methodological, and it is worth stating accurately because the accurate version is more useful. RightShip sells a reporting service to Sea Cargo Charter signatories: it performs the voyage, category and annual carbon intensity and climate alignment calculations and supplies a reporting package with a verification statement. That makes RightShip a calculation and verification service provider to a signatory, not a data source inside the framework’s methodology. The broader relationship between all of these schemes is set out in shipping climate finance and ratings .

Criticism and the recalibration complaint

The best-sourced criticism of the rating comes from RightShip’s own documentation, and it is sharper than most of the external complaints.

On the earlier method: RightShip has acknowledged that the treatment of engine power limitation and shaft power limitation under GHG Rating 1.0 could have led to artificial distortions which incentivised some inefficient vessels while discriminating against others, and that charterers were rejecting vessels which had fitted an EPL or ShaPoLi. That is a candid statement that the rating misgraded ships for a period.

On the moving baseline: RightShip states the rating is dynamic and will almost always compare a different group of vessels at each calculation, and that a vessel’s size score and rating commonly change over time as ships are scrapped and commissioned. This makes longitudinal benchmarking methodologically awkward, and it is the documented core of the owners’ complaint that the goalposts move on a schedule they do not control.

On data quality: an unverified rating rests on IHS inputs, IMO assumptions and sister-ship data, so a material share of ratings rest on proxies with a measured conservative bias.

On the speed assumption: the common speed is drawn from the Fourth IMO GHG Study 2020 with a 10 percent reduction applied for EEXI-driven fleet slowdown. That reduction is a judgment, RightShip has not published its sensitivity, and it applies to every ship in every peer group.

The institutional positions

INTERCARGO published a statement of concern on 16 October 2024, following its Executive Committee meeting in London on 15 October, over RightShip’s decision to reduce the age limit for bulk carrier vetting inspections. The objection was procedural: the decision had been taken without prior consultation with the owners and managers who would be affected, and INTERCARGO raised seafarer workload and noted the vetting inspection regime had been introduced only two years earlier. On 11 December 2024 INTERCARGO welcomed a revised age trigger timeline and, per Chairman Elect John Xylas, the formalisation of an agreement for regular structured consultations. The INTERCARGO Quality Panel, established in 2023, now holds quarterly meetings with RightShip and gave feedback on the RISQ 3.2 inspection questionnaire amendments before implementation.

BIMCO’s position is the 2013 Dry Bulk Marine Risk Assessment Clause, and it remains the strongest institutional criticism of RightShip-linked contracting practice. INTERTANKO’s Vetting Committee holds the general position that inspections should be transparent and justifiable and that their proliferation and cost should be reduced, which is a statement about vetting generally rather than about the GHG Rating.

RightShip’s answer to the design-versus-operational complaint is affirmative rather than defensive. It argues that vessels should be measured according to potential rather than past performance, and offers the case of an A-rated ship returning from a one-year charter with a C CII as the reason the two must not be conflated. The IMO’s own position is that a design index reflects only technical aspects such as engine, hull and propeller optimisation and cannot be used as a performance indicator of operational energy efficiency. Whether a design index is the right basis for a commercial screen is a live argument, not a settled one, and this article does not resolve it.

There is no peer-reviewed critique of the EVDI specifically. The published economics work addresses the regulatory indices instead. A 2024 study in Transportation Research Part D examining container ship fixtures from January 2020 to October 2023 found that a 1 percent decrease in attained EEDI raised time charter rates by 0.10 to 0.12 percent, with the effect stronger for eco-engine vessels. A 2025 paper in Maritime Economics and Logistics examines the effect of CII, AER and EEXI on secondhand prices. No study measures the freight or asset-value effect of a RightShip letter as such.

Limitations

The rating is a private commercial product with no statutory force, no IMO mandate and no right of appeal to a regulator. It can be revised, repriced or restructured by the company that owns it, and its published band edges live on a page that company controls. The comparison with the CII is instructive: the CII’s rating boundaries sit in MEPC.354(78), and changing them requires an IMO resolution.

The letter grades design potential, not measured performance. A ship can earn an A and then run a fouled hull, idle at anchor for months, or steam well above its design point, and none of that appears in the letter. RightShip is explicit that the CII does not feed the rating, so the design letter cannot be read as a proxy for how the ship was actually run. Any vetting decision resting on the letter alone is incomplete by construction.

A letter can move without any change to the ship. The band edges are fixed in standard deviations and the peer distribution slides beneath them, so an owner who does everything right can still lose a band because cleaner tonnage entered the fleet. The 6 December 2023 scale change moved every letter in the fleet at once for reasons unrelated to any individual vessel.

Peer-relative comparison is a poor absolute measure. Two ships in the same band can differ in real-world efficiency depending on trade, draft and loading patterns the design index does not capture, and an A-rated Capesize emits far more per voyage than an E-rated handysize. The letter is a screening instrument inside a peer group and does not survive being lifted out of one.

Calibration is not fully reproducible by an owner. The broad EVDI structure and the band key are published, but the peer-group population at any calculation, the common-speed values by type and the current form of the size-score transform are not. An owner cannot independently reconstruct the number that gates part of its commercial access, and the review of a disputed rating is conducted by the rating’s publisher.

Some figures in wide circulation about the rating have no published source. No count of rated vessels, no market-share percentage of fixtures, no subscription price and no charterer-specific minimum letter could be verified for this article from a first-party or contemporaneous source. Figures of that kind quoted elsewhere should be traced before use. Equally, several claims about the rating’s version history do not survive checking: RightShip publishes GHG Rating 1.0 and 2.0 only, and no later version had been announced at 2 September 2026.

Third-party summaries of GHG 2.0 circulate figures this article does not carry, including a percentage of limited maximum continuous rating, a minimum peer-group population, a deadweight-band widening step and per-type cap speeds in knots. Each traces to a methodology document that is not publicly available, so none is stated here as fact.

Where the rating stands, and what would change it

The IMO Net-Zero Framework has not been adopted, so nothing can responsibly be said about its effect on the rating. MEPC 83 approved the draft Chapter 5 text on 11 April 2025 under Circular Letter No.5005, and the extraordinary session in October 2025 adjourned it. RightShip has announced no methodology version beyond GHG Rating 2.0. Any claim that the rating will re-anchor to a Net-Zero trajectory from 2027 assumes an entry into force that does not exist.

The change with a fixed date is on the data side, and it cuts against the rating’s business model rather than towards it. MEPC.407(84), adopted 1 May 2026, opens the IMO Data Collection System: Parties gain non-anonymized access, the public gains an anonymized database, and a company may request non-anonymized publication of its own ships’ data. It is not yet in force, with deemed acceptance on 1 March 2027 and entry into force on 1 September 2027. To the extent a private vetting rating monetizes informational scarcity about the world fleet, broader access to the underlying operational data erodes part of it.

The CII regime it sits beside is also in motion. MEPC 83 completed Phase 1 of the regulation 28.11 review in April 2025 and agreed a Phase 2 work plan running from Spring 2026 to Spring 2028 across MEPC 84, 85 and 86, covering SEEMP enhancement, further metric development, correction factors and reference-line adjustment. MEPC.407(84) replaces regulation 28.11 with an open-ended review clause, so from 1 September 2027 there is no fixed CII review deadline in the treaty text.

None of that displaces the standing caveat. A private letter on a design index is a screening signal. It works as one input beside the regulated operational measures, and it does not stand in for them.

Related Articles

• Ship efficiency indices : the EEDI, EEXI, EVDI and CII set side by side
• Existing Vessel Design Index : the index the rating is built on
• What is EEDI : the design index for ships contracted from 1 January 2013
• What is EEXI : the design index applied to the existing fleet
• What is CII : the operational carbon intensity rating
• What is AER : the deadweight-based intensity the finance frameworks report on
• EEXI EPL and ShaPoLi : the power-limitation route the rating strips out
• CII rating boundaries and dd vectors : how the IMO sets its band edges
• CII reduction factors G3 : the annual tightening of the regulatory line
• CII corrective action plan : the route for D and E rated ships
• SEEMP I, II and III : the energy-efficiency management plan
• IMO Data Collection System : the fuel consumption reporting regime
• IMO DCS vs EU MRV : the two reporting regimes compared
• EU MRV Regulation : the EU monitoring and reporting layer
• MARPOL Annex VI : the air pollution and GHG annex
• MARPOL Convention : the parent IMO treaty
• IMO GHG Strategy : the 2023 strategy the trajectories align to
• IMO Net-Zero Framework : the adjourned mid-term measure
• Poseidon Principles : the lender-side disclosure framework
• Sea Cargo Charter : the charterer-side disclosure framework
• Shipping climate finance and ratings : the ratings landscape
• Vessel vetting : the vetting function and what a screen tests
• RightShip Safety Score : the safety half of the same platform
• Environmental Ship Index : the port-incentive index
• SIRE tanker inspections : the tanker-side vetting regime
• Port state control : statutory inspection and detention
• Classification society : the bodies that certify a Technical File
• BIMCO CII and emissions clauses : the standard emissions clause family
• Charter party speed and consumption warranties : how a description warranty binds
• Off-hire and performance claims : the claim route when performance diverges
• Time charter party : the contract type most RightShip clauses sit in
• Voyage charter party : the voyage-form counterpart
• NYPE 2015 time charter form : the successor to the form in the Silver Constellation
• Contract of affreightment : multi-shipment programmes with a standing letter floor
• Energy saving devices : the retrofits that earn the plus suffix
• Hull roughness and added resistance : why a fouled hull is invisible to a design index
• Slow steaming : the operational lever that does not move the letter
• Specific fuel oil consumption : the SFC term in the index
• Carbon conversion factors for marine fuels : the carbon factor term
• Speed power trials and ISO 15016 : where the design speed comes from
• Bulk carrier : the principal rated segment
• Oil tanker : the second rated segment
• Bulk carrier size classes : the size bands the peer group draws on
• Tanker size classes : the tanker-side equivalent
• EU ETS for shipping : the regional carbon price a charterer weighs alongside
• FuelEU Maritime explained : the EU fuel intensity regime