The idea in one sentence
EEDI applies to ships built after 2013. The IMO realised that governing only new ships would take decades to meaningfully reduce the fleet’s emissions intensity, so it invented EEXI - the same formula applied retroactively to existing ships, with a strict reduction factor that usually can only be met by limiting engine or shaft power.
The formula
EEXI re-uses the EEDI arithmetic. The numerator is CO₂ per hour at the reference load; the denominator is capacity × reference speed:
Attained EEXI = (Σ P_ME · C_f · SFC + P_AE · C_f,AE · SFC_AE) / (Capacity · V_ref)
[ grams CO₂ per tonne-nautical mile ]
The critical bit is V_ref - the speed the ship actually makes at 75 % of limited Maximum Continuous Rating (MCR). For most existing cargo ships above 2016 build date, V_ref at unlimited MCR gives a number that fails the Required EEXI by 10–30 %. So you limit MCR, V_ref drops, and because power scales with V³, even a modest V cut fixes the ratio.
The target: Required EEXI
Required EEXI = Reference · (1 − Z_EEXI)
The EEDI Reference value comes from MEPC.231(65); Z_EEXI is a one-off ship-type reduction factor:
| Ship type | Z_EEXI |
|---|---|
| Bulk carrier, tanker, gas carrier, container | 20 % |
| General, refrigerated cargo, PCTC | 15 % |
| Ro-Ro cargo, ro-pax | 5 % |
| LNG carrier, cruise | 30 % |
Applied once, at the first IAPP survey on or after 1 January 2023. Pass it and you get an International Energy Efficiency Certificate (IEE Cert) endorsed for EEXI.
EPL vs ShaPoLi
Two ways to declare that you’ve limited power:
- EPL (Engine Power Limitation) - a physical/electronic limiter in the main-engine governor that caps fuel index. Sealed and recorded. An emergency over-ride is allowed, logged, and reported.
- ShaPoLi (Shaft Power Limitation) - instrumentation on the shaft that measures torque and rpm, combines to shaft power, and trips at the limit. Mechanically less invasive than EPL, common on ships where the engine has no OEM-approved EPL kit.
Both are governed by MEPC.335(76) and both require the class society to witness the set-point, stamp the IEE Cert, and verify annually that the seal/program is intact.
What you can actually do
Strategy choice depends on the ship, the trade, and future-proofing:
- EPL/ShaPoLi alone - cheapest, often the whole answer for bulkers and tankers already running at 70 % MCR in practice. No fuel savings (just caps potential), so commercial impact is usually small.
- Hydrodynamic retrofit - bulbous-bow reshape, pre-swirl stator, rudder-bulb - shaves 2–5 % that feeds into both EEXI and the ongoing CII.
- Waste-heat recovery - larger capital, useful on container ships with long sea legs, provides a real Attained EEXI reduction in the numerator.
- Alternative fuel retrofit - switches C_f. LNG drops EEXI from the same engine by ~12 %. Expensive but addresses CII and FuelEU simultaneously.
- Shaft-generator conversion (PTO/PTI) - auxiliary load from the ME gets credited as a Category-B innovative technology, reducing the numerator.
Scope and exclusions
- Applies to cargo and passenger ships of ≥ 400 GT that are subject to MARPOL Annex VI, Chapter 4.
- Excludes ships under a Category X (special designations like platform supply with cargo but no transport work).
- Once EEXI is passed, the survey is done; no annual re-computation. The ongoing metric is CII.
EEXI vs CII - how they differ
| EEXI | CII | |
|---|---|---|
| When | One-off, 2023 or first survey after | Every year from 2023 |
| What | Design reference | Operational outcome |
| Input | Ship particulars + engine SFC | Actual fuel consumed + distance |
| Failure | No IAPP / IEE certificate | D three years → corrective plan |
EEXI can be satisfied purely on paper (via EPL declaration). CII cannot - you have to actually burn less fuel or sail further per tonne-mile.
Charter-party impact
EPL caps maximum speed. If the ship previously warranted 15 knots at 80 % MCR and EPL limits to 65 % MCR, the warranted speed under charter drops to maybe 13.5 knots. BIMCO’s EEXI Transition Clause covers this: it sets out how warrant speeds, performance claims, and under-performance damages are adjusted after EPL/ShaPoLi declaration. New charters increasingly reference the limited MCR directly rather than a speed warranty.
How to compute your ship’s EEXI
Try our EEXI Attained calculator - enter limited-MCR powers, SFOC, capacity basis, and reference speed; it returns Attained EEXI, Required EEXI for your ship type, and the margin. Pair it with the EPL calculator to sanity-check how much MCR you need to cap.