Ship Efficiency Indices: EEDI, EEXI & CII

A ship’s environmental footprint is judged by two different kinds of number, and confusing them is the single most common mistake in this corner of MARPOL. One kind grades the ship the naval architect drew: what it could emit per tonne-mile at a defined reference condition, fixed at the drawing board and proven at the sea trial. The other grades the ship the operator actually ran: what it did emit last year, from the fuel it burned and the miles it sailed. The IMO built three instruments across these two ideas. EEDI gates new ships at design, EEXI gated the existing fleet once in 2023, and the Carbon Intensity Indicator scores the trading fleet every calendar year from reported data. This article is the hub for the EEDI, EEXI, and AER efficiency-indices cluster: it sets the three instruments side by side, explains where each bites, and routes down to the leaf articles and calculators that carry the arithmetic. The EEDI Attained calculator runs the design index, the EEXI Attained calculator runs the existing-ship version, and the CII rating calculator returns the A to E band for a trading year.

The logic of the cluster is worth stating once, because it carries through every leaf. A design index answers one question: at a defined reference speed and load, how many grams of CO2 does this hull and plant emit to move one tonne of cargo one nautical mile. It is a property of the ship, like its deadweight. An operational index answers a different question: across a real year of trading, with real laden and ballast legs, real weather, and real port time, how much CO2 did the ship emit per unit of transport work. It is a property of the voyage history, not the ship. EEDI and EEXI are design indices. CII is operational. AER and cgDIST are the two flavors of the operational metric, distinguished only by whether deadweight or gross tonnage stands in for capacity. Hold that split and the whole system reads as one machine with two faces. The leaf articles take each face apart: what is EEDI, what is EEXI, EEXI EPL and ShaPoLi, what is CII, and what is AER.

The three instruments at a glance

The fastest way to hold the instruments apart is a single table that fixes the four facts that distinguish them: what kind of index it is, which ships it scopes, what unit it measures in, and when it bites. Everything else is detail hung off these four facts.

The table makes the division of labor plain. EEDI and EEXI certify potential and never look at a fuel-oil log; CII ignores the certificate and reads the fuel-oil log. A ship can hold a clean EEXI certificate and still earn an E rating, because a tight engine-power limit lowers the design index without forcing the operator to slow down in service, and the rating depends on how hard the ship was actually pushed. That gap between the certified design value and the earned operational grade is the practical heart of this cluster, and it is why an owner cannot treat the 2023 EEXI pass as the end of the carbon-compliance job.

Why two design indices and one operational index

The split is not arbitrary. A design index can be computed once because the thing it grades, the hull and plant at a reference condition, does not change in service unless the ship is rebuilt. EEDI grades that property for ships ordered after it bit; EEXI grades the same property for the ships that predate it. Two design indices exist only because the fleet straddled the 2013 cutoff: the newbuild stream got EEDI at order, and the legacy stream got a one-time EEXI check in 2023 to close the gap. They are the same arithmetic applied to two cohorts, not two different ideas.

An operational index, by contrast, has to be recomputed every year because the thing it grades, the actual emissions per unit of transport work, changes with every voyage. There is only one operational index because there is only one operating record to read: the year’s fuel and distance. CII is that index, and AER and cgDIST are simply the two capacity bases it runs on. So the count, two design plus one operational, falls straight out of the underlying split: design is a fixed property checked per cohort, operation is a yearly record checked per ship. A naval architect owns the design number; the master, the chief engineer, and the commercial operator own the operational one. The what is CII article works the operational side in full, and what is EEDI and what is EEXI carry the two design cohorts.

EEDI: the design index for new ships

The Energy Efficiency Design Index is a single number that states how many grams of carbon dioxide a new ship emits to move one tonne of cargo one nautical mile, computed at a defined reference condition. The IMO adopted it through Resolution MEPC.203(62) on 15 July 2011, inserting a new Chapter 4 into MARPOL Annex VI, and the amendments entered force on 1 January 2013 under MARPOL’s tacit-acceptance procedure. It was the first mandatory carbon-intensity standard applied to an entire transport sector. A naval architect computes the attained EEDI from the propulsion plant, the fuel, the hull, and the design speed, then proves that number sits at or below the required EEDI for the ship’s type, deadweight, and contract date.

The attained value is a ratio of emitted CO2 to transport work. The numerator is mass of CO2 per hour: the main-engine power, taken at 75% of installed maximum continuous rating after deducting any shaft-generator and innovative-technology power, multiplied by the specific fuel consumption from the engine’s NOx Technical File and the fuel carbon factor Cf, summed with the auxiliary load on the same basis. The carbon factor is tabulated by fuel in Resolution MEPC.364(79): 3.114 tonnes CO2 per tonne for heavy fuel oil, 3.206 for diesel and gas oil, and 2.750 for LNG, among others. The denominator is transport work, capacity times reference speed, where capacity is deadweight for most cargo ships and gross tonnage for passenger and ro-pax types. The EEDI Attained calculator runs this ratio, and the bare formula sits inline below.

The reference line and the phase reduction factors

EEDI does not hold every ship to one number; it holds each ship type to a curve. The required EEDI starts from a reference line, a regression of the attained index against deadweight fitted to ships built between 1999 and 2009, in the form a times b to the power minus c, where b is the ship’s capacity and a and c are coefficients tabulated by type. That reference line represents the 2013 fleet-average intensity for a ship of that type and size. The required value is then the reference line pulled down by a reduction factor X, so a larger ship is allowed a lower CO2 per tonne-mile than a small one, reflecting the real economy of scale in moving cargo by sea. The EEDI reference-line calculator reads off the line for a given type and deadweight, and the EEDI required calculator applies the reduction.

The reduction factor is where EEDI tightens, and it tightens across build years, not within a ship’s life. The required line steps down through phases keyed to the ship’s contract or delivery date. Phase 0 applied to ships contracted from 2013, Phase 1 from 2015, Phase 2 from 2020, and Phase 3 from 2022 onward (brought forward for several large types). By Phase 3 a bulk carrier and tanker must beat a required line 30% below the 2013 baseline, container ships up to 50% for the largest sizes, with the exact percentage set per type and size band in the Regulation 24 table of the revised Annex VI. The EEDI phase-factor calculator returns the X for a given type, size, and date. A ship built under Phase 1 is held to its Phase 1 line for life; the later phases bind only the ships ordered under them.

Correction factors and innovative technology

The bare ratio is the single-engine, single-fuel, no-shaft-generator case. The full MEPC.231(65) method wraps it in correction factors that stop the basic ratio penalizing design features that are not inefficiency. The ice-class factor fj discounts the extra installed power an ice-strengthened hull needs to break ice, because grading a Baltic trader against the engine it needs in February would be perverse; the ice-class correction calculator reads it off the ice class. The weather factor fw is a voluntary coefficient below 1.0 that credits the speed a ship still holds in representative wind and waves. The capacity correction fc and the cubic-capacity factor fcubic handle chemical tankers and other types where the deadweight overstates usable cargo space; the fcubic calculator handles that adjustment. Innovative energy-efficiency technologies, wind assistance, air lubrication, and the like, enter through a dedicated credit term that subtracts their effect from the numerator. The innovative-technology calculator computes that credit, and the energy-saving devices article covers the hardware that earns it.

EEXI: the existing-ship design index

The Energy Efficiency Existing Ship Index extends the EEDI logic backwards across ships already in service. The IMO adopted it on 17 June 2021 as part of the revised MARPOL Annex VI in Resolution MEPC.328(76), and it took effect on 1 November 2022. Every cargo and passenger ship of 400 GT and above on international voyages had to demonstrate an attained EEXI at or below a required EEXI value at its first periodical, intermediate, or renewal IAPP survey on or after 1 January 2023. The reason it exists is plain arithmetic: EEDI binds only ships ordered after it entered force, so the millions of deadweight tonnes built before 2013 carried no design-carbon obligation at all until EEXI closed that gap with a one-time check.

EEXI uses the same design-index family as EEDI, with the calculation method set in Resolution MEPC.333(76). The reference power point is 83% of maximum continuous rating, or 83% of the limited MCR where the engine has been derated, and the reference speed is the speed the ship makes at 75% of that MCR in deep water under the reference loading condition. The required EEXI uses the EEDI reference-line parameters with EEXI-specific reduction factors carried in the Regulation 25 tables. The defining difference from CII is in the verb tense: EEXI is checked once and the certified attained value is fixed for the ship’s life, unless a major conversion changes the inputs. The EEXI Attained calculator reproduces the design value and the EEXI required calculator returns the target to beat.

EPL and ShaPoLi: the power-limitation route

Because the EEXI formula rewards a slower reference speed, the cheapest path to compliance for most owners is to cap installed power so the reference speed drops, rather than touch the hull or the fuel. The physics does the work: resistance rises with roughly the square of speed and the power to overcome it with roughly the cube, so a modest cut in available MCR drops the reference speed enough to move the whole ratio below the required line. Two mechanisms implement the cap. An Engine Power Limitation (EPL) limits the engine’s fuel index, mechanically or in software, so the engine cannot develop more than the declared limited MCR. A Shaft Power Limitation (ShaPoLi) instead measures and limits the torque on the shaft, leaving the engine untouched but capping the power that reaches the propeller. The legal hook, the override mechanism, and the onboard paperwork all sit in Resolution MEPC.335(76), and the EEXI EPL and ShaPoLi article works the two side by side.

The reserve-power question is the one genuine controversy in the EEXI design. A limiter that caps the engine to a level a bulker or tanker already ran at in practice costs almost nothing, because it caps a power band the ship rarely used; an owner running at 65% to 70% MCR loses little real capability by declaring a limit at that level. The risk is on the day the ship needs more, for weather routing, schedule recovery, or maneuvering in a heavy seaway, which is why both mechanisms allow an overridable limit: the master can break the cap in a documented emergency, with the override logged for the surveyor. The EPL calculator returns the power fraction needed to close a given gap, and the ShaPoLi calculator handles the shaft-limit case. Power limitation, not retrofitting, became the dominant EEXI response across the dry-bulk and tanker fleets for exactly this reason: it is the lowest-cost way to satisfy a design index that rewards a slower speed.

CII: the operational rating

The Carbon Intensity Indicator is the operational half of the package adopted alongside EEXI in MEPC.328(76). Where EEXI grades the ship’s design once, CII grades the ship’s operation every calendar year, and it issues a letter. The legal spine is short: MEPC.336(76) was adopted at MEPC 76 in June 2021, entered force on 1 November 2022 as Regulation 28 of MARPOL Annex VI, and the first measured reporting year was 2023, with the first ratings issued in 2024. It applies to ships of 5,000 GT and above on international voyages, the same threshold as the IMO Data Collection System that supplies the fuel-and-distance data the rating runs on. Four guidelines resolutions do the arithmetic the regulation only points to: MEPC.337(76) sets the reference lines, MEPC.338(76) set the reduction factors, MEPC.339(76) defined the rating boundaries, and the 2022 pair MEPC.354(78) and MEPC.355(78) refined the factors and added correction factors and voyage adjustments.

The attained CII for a year is the ship’s total CO2 emitted, from the fuel consumed times each fuel’s carbon factor, divided by the transport-work proxy, capacity times distance sailed. The required CII is the year’s target: the 2019 reference line for that ship type and size, pulled down by the annual reduction factor Z. The rating then compares attained to required: the ratio is placed against the d1 to d4 boundary vectors for the ship type to land in one of five bands. The CII attained calculator runs the numerator and denominator, the CII required calculator returns the target, and the CII attained-vs-required check shows the headroom or deficit directly.

The A to E rating and the corrective action plan

The five bands run from A to E, set by where the attained-to-required ratio falls against the type-specific boundary vectors. A is major superior, B minor superior, C moderate, D minor inferior, and E inferior, with C the pass mark. The boundary vectors are the current G4 set in MEPC.354(78): for a bulk carrier the edges are 0.86, 0.94, 1.06, and 1.18; for a tanker 0.82, 0.93, 1.08, and 1.28; for a container ship 0.83, 0.94, 1.07, and 1.19. A ratio below d1 is an A, above d4 an E, and the spread between d1 and d4 differs by type because the operational scatter differs by trade. The CII rating calculator returns the band for a given attained and required pair.

The rating has teeth through the SEEMP. A ship rated D for three consecutive years, or E in a single year, must develop a corrective action plan documenting how it will return to a C or better, and have that plan approved and incorporated into its SEEMP Part III. The plan is not a fine, but it is a paper trail that charterers, financiers, and port-state inspectors can read, and a persistent poor rating shows up in the BIMCO CII clauses that allocate the rating risk between owner and charterer. The CII corrective-action-plan article and the 3-year corrective-plan calculator work the recovery path, and the cheapest operational lever is usually speed, covered in slow steaming and CII.

The Z reduction-factor trajectory to 2030

The reduction factor Z is the part that bites year after year, because it pulls the required line down even for a ship that never changes how it operates. MEPC.338(76) set Z at 5% for 2023, then 7% for 2024, 9% for 2025, and 11% for 2026, all measured against the 2019 reference line, a flat two percentage points a year. The post-2026 trajectory was left open in the original guidelines and was settled at MEPC 83. Resolution MEPC.400(83), adopted on 11 April 2025, amended the G3 reduction-factor guidelines to extend the schedule through 2030 at a steeper step: 13.625% for 2027, 16.25% for 2028, 18.875% for 2029, and 21.5% for 2030. The 21.5% endpoint lines the indicator up with the 2023 IMO GHG Strategy ambition to cut carbon intensity per transport work by at least 40% by 2030 against the 2008 baseline.

The shape of the table is the substance of the policy. The step rises from 2.0 points a year through 2026 to 2.625 points a year from 2027, so the bar does not just keep descending, it descends faster. A ship sitting comfortably inside a C in 2024 can drift into a D by 2027 on an unchanged operating pattern, because the required line has moved underneath it while its attained value held steady. The year-on-year improvement check projects that drift, and any multi-year fleet plan has to model the moving target rather than this year’s grade. The trajectory is also the reason CII compliance is a treadmill, not a gate: passing in one year buys no relief in the next.

AER and cgDIST: the two operational metrics

The CII numerator-and-denominator is itself one of two closely related metrics, and which one a ship uses depends on its type. Both are supply-based: they divide annual CO2 by the product of a capacity term and the distance sailed, so they measure intensity against the ship’s carrying potential rather than against the cargo it actually moved. The difference is the capacity term. The Annual Efficiency Ratio (AER) uses deadweight tonnage, giving grams of CO2 per deadweight-tonne-mile, and it applies to most cargo ship types: bulk carriers, tankers, container ships, gas carriers, and general cargo ships. The what is AER article and the AER calculator run it.

cgDIST uses gross tonnage instead of deadweight, giving grams of CO2 per gross-tonne-mile, and it applies to the ship types where deadweight is a poor proxy for what the ship is built to carry: cruise passenger ships, ro-ro cargo ships, ro-ro passenger ships, and vehicle carriers. A car carrier’s deadweight is dominated by the steel of its decks, not by the cars it carries, so dividing emissions by deadweight would flatter a heavily built ship and penalize a light one for no operational reason; gross tonnage, a volume measure, tracks the enclosed space the ship sells far better. Both metrics are reported through the same IMO Data Collection System data elements, and both feed the same A to E rating against type-specific boundaries. The point to carry away is that AER and cgDIST are not competing standards: they are the same operational metric with the capacity basis chosen to fit each ship type’s economics.

AER against the other carbon metrics

AER is also the lending and chartering industry’s working metric, which is why it has a life beyond MARPOL. The Poseidon Principles, the framework banks use to align ship-finance portfolios with the IMO climate ambition, measure a financed ship’s climate alignment on its AER, and the Sea Cargo Charter does the same for charterers. RightShip’s GHG rating leans on the same deadweight-based intensity. The reason the finance side settled on AER rather than the more cargo-accurate Energy Efficiency Operational Indicator (EEOI) is data availability: AER needs only fuel, distance, and deadweight, all reported through the IMO DCS, while the EEOI needs the actual cargo carried on each leg, which is commercially sensitive and not centrally reported. AER trades a little accuracy for a number every ship can produce from data it already files, and that tradeoff is why it became the common currency.

The cgDIST case for ro-ro and cruise tonnage is worth stating plainly because it is where deadweight fails hardest. A 60,000 GT car carrier might have a deadweight near 20,000 tonnes, most of it the steel of a dozen vehicle decks rather than cargo, so an emissions-per-deadweight number rewards a flimsy ship and punishes a well-built one for carrying the same number of cars. Gross tonnage tracks enclosed volume, which is what a vehicle carrier or a cruise ship actually sells, so dividing by GT lines the metric up with the commercial product. The cgDIST calculator runs the gross-tonnage form for exactly these ship types, and the choice of basis is fixed per type in the CII guidelines, not left to the operator.

Where each number comes from: the verification and data chain

The three indices look similar on paper, but the chain of custody behind each number is different, and that difference decides who can challenge it. EEDI and EEXI are verified by a Recognized Organization, almost always a classification society, against a documented Technical File. The attained EEDI rests on a sea trial: the ship runs a measured mile in deep water, the speed-power curve is fitted, and the certified attained value is locked to the EEDI Technical File and the IEE (International Energy Efficiency) Certificate. A surveyor checks the inputs (the engine’s certified SFC from the NOx Technical File, the reference speed from the tank test corrected to the sea trial, the correction factors claimed) but does not re-run the trial. EEXI follows the same paper trail through Resolution MEPC.333(76): an attained value, a preverification of the calculation, and an onboard EEXI Technical File approved before the first survey on or after 1 January 2023. The IEE Certificate carries both indices once issued.

CII runs on a different feedstock. It does not read a Technical File; it reads the ship’s IMO Data Collection System report. Every ship of 5,000 GT and above files annual fuel consumption by fuel type and total distance sailed to its flag administration through the DCS, the administration issues a Statement of Compliance for the data, and the verifier (again a Recognized Organization in most flags) computes the attained CII from those reported totals. That same reporting spine, the IMO DCS alongside the EU MRV system, is the subject of the emissions monitoring and reporting hub, which works the measurement, verification, and submission cycle that produces the fuel-and-distance totals the rating runs on. The same data elements that satisfy the DCS feed the rating, so the operational index is only as good as the noon-report and bunker-delivery-note discipline behind it. A ship that misreports distance or fuel does not get a wrong certificate; it gets a wrong grade, and the grade is what charterers read.

The practical upshot is who can argue with the number. An owner who disputes an EEDI value argues with the trial data and the calculation method, a one-time technical fight settled before delivery. An owner who disputes a CII grade argues with a year of operating data already filed under the DCS, and the only levers left are the correction factors and voyage adjustments in MEPC.355(78): ice transit, extended port stays, ship-to-ship transfer time, and a handful of trade-specific allowances. The CII voyage-adjustment calculator and the CII fuel-mix correction work those allowances, and the AER attained-vs-required check shows the deadweight-based margin directly.

A worked CII drift, year on year

The reason CII is a treadmill is best shown with one ship held steady. Take a 75,000 dwt Panamax bulk carrier whose operation does not change between 2024 and 2027: the same trade, the same average speed, the same laden-to-ballast ratio, so its attained AER holds at a flat value year after year. Its required CII, though, is the 2019 reference line pulled down by the year’s Z factor, and Z climbs from 7% in 2024 to 13.625% in 2027. Against an unchanged attained value, the ratio of attained to required rises every year because the denominator (the required line) keeps shrinking. A ship comfortably mid-C in 2024 can sit at the C/D boundary by 2026 and slip to a D in 2027 without burning one extra tonne of fuel, purely because the bar moved under it.

The bulk-carrier boundary vectors make the size of the move concrete. The C band for a bulker runs from a ratio of 0.94 (the C/B edge) to 1.06 (the C/D edge) in MEPC.354(78). A ship attaining exactly its 2024 required value sits at a ratio of 1.00, comfortably inside C. Hold the attained value flat while Z moves from 7% to 13.625% and the required value drops by roughly 7% over those three years, so the same attained number now reads as a ratio near 1.07, just past the D edge. The year-on-year improvement check projects exactly this drift, and the CII corrective-trajectory calculator plots the attained-value path a ship must walk to stay inside C as the line descends. The lesson for any fleet plan is that this year’s grade is not next year’s grade, and a multi-year budget has to model the moving target rather than the current pass.

How the cluster fits together

The leaf articles under this hub each carry one instrument’s full treatment, and they cross-link to each other because the instruments share machinery. What is EEDI works the design index from MEPC.203(62) through the phase factors and the correction terms. What is EEXI extends that arithmetic to the existing fleet under MEPC.328(76), and EEXI EPL and ShaPoLi takes the power-limitation route apart in detail. What is CII carries the operational rating, the Z trajectory, and the corrective-action machinery, with slow steaming and CII, the CII corrective action plan, and the BIMCO CII clauses as its satellites. What is AER covers the operational metric and its life in ship finance.

The cluster sits inside a wider decarbonization program. The efficiency indices are the regulatory pressure; the response is partly operational (speed and routing) and partly hardware, which is where energy-saving devices and the broader decarbonization technologies hub come in, and partly a fuel switch, covered in the decarbonization and alternative fuels hub. The indices are also being overtaken at the policy frontier: the IMO Net-Zero Framework and the GFI moves the regime from a carbon-intensity rating toward a well-to-wake fuel-intensity standard with a price attached, the mid-term measure approved at MEPC 83 alongside the CII trajectory extension. The design and operational indices remain in force underneath that new layer, and a ship in 2030 will carry an EEDI or EEXI certificate, an annual CII rating, and a GFI obligation at once.

Regulatory basis and currency

The cluster rests on a stack of resolutions that amend MARPOL Annex VI rather than one master rule, so the currency of each instrument depends on which resolution is the latest in force. EEDI traces to Resolution MEPC.203(62), adopted 15 July 2011, in force 1 January 2013, with the calculation method carried in MEPC.231(65) and later refinements. EEXI and the operational CII both arrive with the 2021 revised Annex VI in Resolution MEPC.328(76), adopted 17 June 2021, in force 1 November 2022, with the EEXI calculation method in MEPC.333(76) and the power-limitation guidance in MEPC.335(76). CII itself is Regulation 28 of the revised Annex VI, given operational teeth by MEPC.336(76).

The four CII guidelines resolutions are the ones that move. MEPC.337(76) sets the reference lines (G2), MEPC.338(76) set the original reduction factors through 2026 (G3), MEPC.339(76) defined the first rating boundaries (G4), and the 2022 pair MEPC.354(78) and MEPC.355(78) refined the boundaries and added the correction factors and voyage adjustments. The most recent change is Resolution MEPC.400(83), adopted 11 April 2025 at MEPC 83, which amended the G3 guidelines to extend the reduction-factor schedule through 2030 at the steeper 2.625-point step. Any compliance figure quoted in this hub is keyed to that stack as it stood after MEPC 83. The IMO has flagged a review of the whole short-term measure, so the boundaries and factors past 2026 are settled in resolution but open to revision, and a multi-year plan should track the resolution index rather than treat any single figure as permanent. The marpol-cii-required calculator and the marpol-cii-rating calculator carry the regulation-keyed forms of the operational arithmetic, and marpol-eedi-required and marpol-eexi-required do the same for the design indices.

Limitations

These instruments measure what they were built to measure, and reading them as more than that is a recurring error. EEDI and EEXI are design indices computed at a single reference condition; they say nothing about how a ship is actually operated, so a clean EEXI certificate is no guarantee of a good CII rating, and the gap between the two is real and routine. The attained EEDI and EEXI depend on inputs (the engine’s certified specific fuel consumption, the reference speed from the tank test and sea trial, the correction factors claimed) that a surveyor verifies but that carry their own measurement uncertainty; the certified value is a defensible estimate, not a field measurement of in-service emissions.

The CII rating inherits the limits of its inputs and its design. It runs on deadweight or gross tonnage as a capacity proxy, not on cargo actually carried, so a ship that sails part-laden or in ballast is graded against its full capacity regardless, and a trade with heavy ballast legs is structurally disadvantaged against a trade with backhaul cargo. The correction factors and voyage adjustments in MEPC.355(78) soften some of this for specific trades, but the metric remains a fleet-management indicator rather than a precise emissions account. The reduction-factor trajectory stated here is the schedule in force: MEPC.338(76) through 2026 and MEPC.400(83) for 2027 to 2030. That trajectory and the rating boundaries are subject to IMO review and can change, and the wider regime is shifting toward the GFI standard, so a multi-year compliance plan must track the current resolutions rather than treat any single year’s factors as permanent. None of the linked calculators replaces the verified figures in a ship’s EEDI or EEXI Technical File, its IMO DCS report, or a class society’s CII statement of compliance for the specific ship and year.

See also

• What is EEDI: the design index for new ships, the reference line, and the phase reduction factors.
• What is EEXI: the one-time design check for the existing fleet under MEPC.328(76).
• EEXI EPL and ShaPoLi: the engine-power and shaft-power limitation routes to compliance.
• What is CII: the operational A to E rating, the Z trajectory, and the corrective-action machinery.
• What is AER: the Annual Efficiency Ratio and its role in Poseidon Principles lending.
• Slow steaming and CII: the speed lever, the cheapest route to a better operational rating.
• Energy-saving devices: the hardware that earns EEDI innovative-technology credit and improves CII.
• Decarbonization and alternative fuels: the wider policy and fuel-transition program the indices sit inside.
• Decarbonization technologies: the onboard hardware deployed to meet the indices.
• IMO Net-Zero Framework and the GFI: the well-to-wake fuel-intensity standard approved at MEPC 83.
• Emissions monitoring and reporting: the IMO DCS and EU MRV reporting spine that feeds the operational rating.
• EEDI Attained calculator: the design index from plant, fuel, hull, and speed.
• EEXI Attained calculator: the existing-ship design index with a power limit applied.
• EPL calculator: the engine-power fraction needed to close an EEXI gap.
• ShaPoLi calculator: the shaft-power limit equivalent.
• CII rating calculator: the A to E band from attained and required CII.
• CII attained-vs-required check: the headroom or deficit against the year’s target.
• AER calculator: the Annual Efficiency Ratio in grams CO2 per deadweight-tonne-mile.