CII Corrective Plan Projector: D or E to C

A D or E rating isn’t a verdict on a single year so much as a requirement to plan the next ones. Under MARPOL Annex VI Reg.28, a ship that rates D for three consecutive years, or E in any single year, must record a corrective action plan in its SEEMP Part III and aim it at returning to at least a C rating. The hard part isn’t the obligation, it’s the moving target. The required CII line tightens every year through the annual reduction factor Z, so a plan that only closes the gap to today’s C boundary is already behind. This projector computes the per-year attained-CII reduction that lands the ship on the C boundary against the required line in the final plan year, not against today’s.

It pairs with the CII rating calculator, which returns the letter, and the CII attained calculator, which builds the attained figure from fuel and distance. Where the rating page answers what grade the ship holds, this page answers how fast the ship has to improve to climb out of it.

How to use this calculator

1. Select the ship type; this sets the MEPC.354(78) rating boundaries (d-vectors) used to place the ratio on the A to E scale.
2. Enter the current attained CII in gCO2 per dwt-nm, from the verified annual DCS report or the CII attained calculator.
3. Enter the current required CII for the same year: the reference line $a \cdot \text{Capacity}^{-c}$ reduced by that year’s Z factor.
4. Select the current year. It anchors the start of the plan and the Z step the required line follows.
5. Set the plan horizon in years, normally 3.
6. Read the current rating ratio, the target ratio at the C boundary $d_3$, and the annual attained-CII reduction needed to reach it by the final year.

What the corrective plan has to contain

The SEEMP Part III is not a free-text promise. MEPC.347(78), updated by MEPC.376(80), sets the framework: an implementation plan with a description of the corrective actions, the expected effect of each on the attained CII, and a timeline for putting them in place. The plan has to be developed taking into account the guidance on corrective actions, and it is submitted to the Administration or a recognized organization for the Statement of Compliance to remain in good standing. The flag state then checks the ship against the plan at each annual verification under the Data Collection System.

What this calculator supplies is the quantitative spine of that plan: the size of the attained-CII reduction the measures collectively have to deliver, spread across the horizon. It does not pick the measures. A plan that claims a 4.7% annual cut without naming the hull cleaning, the propeller polish, the trim optimization, or the speed reduction that produces it is the kind of plan a verifier sends back.

Trigger rules in one place

The asymmetry at the bottom is deliberate. A single D carries no immediate duty, and a ship can sit at D for two years while it works the problem. The third consecutive D pulls the trigger, and a single E pulls it immediately, with no two-year grace. The three-consecutive-D count is unforgiving in one respect: it counts years against a line that moved underneath the ship, so a vessel can earn three D ratings with unchanged operation simply because the required CII tightened each year.

Formula, assumptions, and limits

Formula

The projector solves for the constant annual fractional reduction $g$ that takes today’s attained CII down to the C boundary against the final-year required line:

The final-year required CII follows the reference line as Z tightens, so it can be written from today’s required value and the two years’ Z factors:

Derivation

The target at the end of the plan is a ratio $r = \text{CII}_{\text{att,end}} / \text{CII}_{\text{req,end}} \le d_3$, the top of the C band. Setting the target attained CII to exactly the boundary gives $\text{CII}_{\text{att,end}} = d_3 \cdot \text{CII}_{\text{req,end}}$. Reducing the attained CII by a constant fraction $g$ each year over $N$ years multiplies it by $(1-g)^N$, so $\text{CII}_{\text{att,now}} \cdot (1-g)^N = d_3 \cdot \text{CII}_{\text{req,end}}$. Solving for $g$ gives the formula above. The straight-line constant-fraction path is the simplest trajectory that satisfies the endpoint; it is not the only one, and real plans rarely cut at a flat rate (see Assumptions).

Assumptions

• The required line tightens at the scheduled Z rate only. The 2023 to 2026 steps are 5%, 7%, 9%, 11% from MEPC.338(76); the 2027 to 2030 steps are 13.625%, 16.25%, 18.875%, 21.5% from MEPC.400(83), a 2.625-point annual increase to 21.5% below the reference line by 2030. The reference line coefficients $a$ and $c$ are assumed unchanged across the horizon.
• The d-vector for the ship type is the current G4 set from MEPC.354(78). The bulk-carrier C boundary $d_3$ is 1.06; values differ by type (tanker 1.08, container 1.07, LNG carrier of 100,000 dwt and above 1.06, ro-ro passenger 1.14).
• The path is constant-fraction. The output is the level annual cut that hits the endpoint; the plan can front-load or back-load the real measures around it.
• Capacity and ship type are fixed for the horizon. A conversion, a re-rate, or a deadweight change would move both the reference line and the boundary.

Worked example

A bulk carrier holds an attained CII of 6.2 gCO2 per dwt-nm in 2025, against a required CII of 5.5 for that year. The ratio is $6.2 / 5.5 = 1.127$. The bulk-carrier d-vector is $d_3 = 1.06$, $d_4 = 1.18$, so a ratio of 1.127 is a D. The ship has rated D for three years running and now needs a corrective plan over an $N = 3$ year horizon, so the plan ends in 2028.

First, project the required line forward. The 2025 reference value is $5.5 / (1 - 0.09) = 6.044$. As Z tightens, the required CII falls each year:

The final-year required CII is 5.062, which the shortcut confirms: $5.5 \cdot (1 - 0.16250)/(1 - 0.09) = 5.5 \cdot 0.9203 = 5.062$. The target attained CII at the C boundary is $d_3 \cdot 5.062 = 1.06 \cdot 5.062 = 5.366$. The required total fraction is $5.366 / 6.2 = 0.8654$, so the cube root gives the annual factor: $0.8654^{1/3} = 0.953$, and $g = 1 - 0.953 = 0.047$, a 4.7% annual reduction in attained CII.

Step it down to check: $6.2 \to 5.908 \to 5.630 \to 5.366$, and $5.366 / 5.062 = 1.06$, exactly the C boundary. The ship has to shed roughly 13.5% of its attained CII over three years, not the 9% that closing the gap to today’s line alone would suggest, because the line drops a further 7.9% under it across the horizon.

In practice the 4.7% per year is a target, not a recipe, and plans don’t deliver it as a flat cut. Year-1 measures are the ones a superintendent can act on inside a docking window: hull cleaning, propeller polishing, and trim optimization, which recover efficiency lost to fouling. The later years lean on operational and fuel-side change, speed management and fuel switching, that takes longer to embed. The split front-loads the certain measures and leaves the harder reductions for when the line is tightest. The specific savings each measure yields are ship-specific and out of scope for this tool, so the projector states the required total reduction and leaves the measure-by-measure attribution to the plan.

Edge cases and limits

The projector returns a non-positive reduction when the ship is already on track: if today’s attained CII already sits at or below $d_3$ times the final-year required line, no cut is needed and the plan is a hold-the-line exercise. Crossing the 2026 to 2027 boundary inside a horizon picks up the larger 2.625-point Z step, so a plan that starts in 2026 faces a steeper required total reduction than the same gap starting in 2025. The 2031-and-later Z factors are not yet adopted, so a horizon that runs past 2030 uses the 2030 value as a flat assumption and should be read as provisional.

Regulatory basis

MARPOL Annex VI Reg.28 (in force 1 November 2022, CII in force 1 January 2023 via MEPC.328(76)) sets the corrective-plan obligation. The SEEMP Part III framework is MEPC.347(78), updated by MEPC.376(80). The annual reduction factors are MEPC.338(76) for 2023 to 2026 and MEPC.400(83) for 2027 to 2030 (adopted 11 April 2025 at MEPC 83). The rating boundaries are the current G4 d-vectors from MEPC.354(78), the 2022 amendment revising the original MEPC.339(76). The unified interpretation of the corrective-action and SEEMP Part III requirements is carried in MEPC.1/Circ.795 (Rev.9), the consolidated index of MARPOL Annex VI unified interpretations.

Common errors

1. Targeting today’s required line. Sizing the plan against the current year’s C boundary ignores the Z tightening and underestimates the cut, here by about a third (9% versus 13.5% over three years).
2. Reading 4.7% per year as “do 4.7% in year 1.” The output is the level annual fraction that hits the endpoint; the real plan front-loads dock-window measures and leaves fuel-side change for later, so a flag verifier wants the per-year measure schedule, not the flat number.
3. Quoting a ratio without the ship type. A target of $r \le 1.06$ is the bulk-carrier boundary; on a tanker the C boundary is 1.08 and on a ro-ro passenger ship 1.14, so the same attained CII can need a smaller cut on a more tolerant d-vector.
4. Treating the plan as a penalty. CII has no euro price; the consequence is the plan and the flag-state check on the Statement of Compliance, separate from the EU ETS bill and the FuelEU penalty.
5. Holding capacity fixed after a re-rate. A deadweight change or conversion moves both the reference line and the boundary, invalidating a plan keyed to the old figures.

When to use this versus the trajectory calculator

This projector answers a planning question: given where the ship is and a horizon, what annual attained-CII reduction returns it to C. It solves for the cut. The CII corrective trajectory calculator runs the inverse, taking a chosen reduction path and showing the rating year by year, which is what a verifier reads when checking a plan’s claimed steps against the moving line. Use this page to size the plan; use the trajectory page to test a specific set of measures against the rating bands across the years.

For the underlying letter and the attained-to-required ratio in any single year, the CII rating calculator is the source, and the attained-versus-required calculator holds the attained steady to show how the grade erodes as the line tightens.

Limitations

The tool models the arithmetic of the line, not the ship. It assumes a constant-fraction path, fixed reference coefficients, and the adopted Z schedule, and it targets the C boundary exactly rather than building in margin. A plan filed at exactly $r = 1.06$ is a D the moment the line tightens again, so an operator usually aims below the boundary for headroom. The projector does not estimate what each measure saves, does not account for trade-pattern change, weather routing, or ballast-leg share, and does not model the EU ETS or FuelEU exposure that runs alongside CII on European voyages. It sizes the gap; the SEEMP Part III plan, the measures, and the verification close it.

Further reading

• CII corrective action plan
• SEEMP I, II and III
• What is CII?
• CII rating calculator
• CII attained calculator
• CII corrective trajectory calculator

Frequently asked questions

What triggers a SEEMP Part III corrective action plan?

Two outcomes trigger it under MARPOL Annex VI Reg.28. A ship rated D for three consecutive years must develop a plan, and a ship rated E in a single year must develop one at once. The plan goes into the SEEMP Part III, sets out how the ship will return to at least a C rating, and is submitted to the Administration or a recognized organization before the next annual verification.

How long is the CII corrective plan period?

The corrective action plan covers the steps the ship will take from the year it is filed onward, and operators normally frame it over a three-year horizon to match the rolling review cycle and the three-consecutive-D logic that triggered it. There is no fixed statutory horizon in Reg.28; the test is that the documented measures are expected to bring the attained CII back to the C band, and the flag state checks progress at each annual DCS verification.

Does a D rating mean a fine?

No. CII carries no euro price. It is an administrative operational measure, so a D or E rating triggers a corrective action plan, not a penalty. The financial exposure on European voyages comes from the separate EU ETS and FuelEU Maritime regimes, which do price emissions. The CII consequence is the plan and the flag-state scrutiny attached to the Statement of Compliance, not a charge per tonne.

Does the corrective plan target this year's required CII or a future one?

A future one. The required line tightens every year through the Z factor, so a plan that only matched today's C boundary would already be a D by the time it finished. This projector targets the C boundary against the required line in the final plan year, which is why the per-year reduction it returns is steeper than the gap to today's line alone.