EEXI: Engine Power Limitation and ShaPoLi

Background: why power limitation became the dominant compliance route

EEXI under MARPOL Annex VI Reg.25

The Energy Efficiency Existing Ship Index was introduced by Resolution MEPC.328(76), adopted 17 June 2021 at the 76th session of the IMO Marine Environment Protection Committee. The amendments to MARPOL Annex VI entered force 1 November 2022, with first compliance required at the first annual, intermediate, or renewal IAPP survey on or after 1 January 2023.

MARPOL Annex VI Regulation 25 establishes the EEXI framework. Reg.25.4 requires every ship of 400 GT and above on an international voyage to hold an International Energy Efficiency Certificate (IEEC) showing that the attained EEXI does not exceed the Required EEXI for that ship’s type and size. The Required EEXI is calculated per Reg.25.3 using the same reference-line parameters as EEDI but with a one-time reduction factor applied immediately rather than phased over decades as for new ships.

The attained EEXI is calculated per MEPC.350(78) (the 2022 Guidelines on the method of calculation of attained EEXI, adopted at MEPC 78 in June 2022). The formula uses actual specific fuel oil consumption from the ship’s EIAPP Certificate, the reference speed at 75% of limited MCR (not original MCR), and capacity defined per the ship type.

The compliance gap for existing ships

The 2021 IMO impact assessment (MEPC 76/INF.42) estimated that approximately 75% of the existing fleet above 5,000 GT would not meet the Required EEXI without intervention. Pre-EEDI ships were optimised for design speed and cargo carrying rather than CO2 efficiency; engines were routinely over-sized by 10-20% above the power needed for sustained commercial service. Hull forms, propellers, and superstructures were designed before the EEDI reference lines existed.

Technical measures available to close the gap, including engine retrofits, propeller replacement, hull coating improvement, and energy-saving devices such as Mewis ducts and pre-swirl stators, were evaluated and found insufficient or uneconomic for most of the affected fleet. The IMO Working Group on EEXI implementation (2020-2021) concluded that power limitation would be the most cost-effective pathway for the large majority of ships.

The IMO’s own estimate: roughly 70% of existing-ship EEXI compliance has been achieved through EPL or ShaPoLi rather than through technical or operational measures alone. The remaining 30% combined hull retrofit, propeller work, and fuel-system upgrades with or without power limitation.

EEXI survey and certification

Resolution MEPC.351(78), adopted at MEPC 78 alongside the attained-EEXI calculation guidelines, provides the survey and certification framework. The verifying authority is the Administration (flag state) or a Recognised Organisation (classification society) acting on its behalf. The class society examines the EEXI Technical File, confirms the limited MCR method and the attained EEXI value, and issues the IEEC endorsement.

The EEXI Technical File is the document package that records the ship’s specific fuel oil consumption data, the attained EEXI calculation, the chosen compliance method (EPL or ShaPoLi or technical measure), and the Onboard Management Manual (OMM) reference. It stays on board for the life of the ship.

Regulatory basis in detail

Resolution MEPC.335(76): EPL guidelines

MEPC.335(76) was adopted at the same session as the parent EEXI amendments, 17 June 2021. It provides the technical guidelines for Engine Power Limitation as an EEXI compliance method and covers:

• The technical methods by which the engine MCR may be limited (permanent mechanical modifications or sealable software and mechanical limits).
• The categorisation of EPL into permanent EPL and sealable EPL.
• The reserve-power (emergency override) procedure for sealable EPL.
• The documentation requirements: the Onboard Management Manual specifying how EPL is implemented, monitored, and overridden.
• The verification procedures for the limited MCR, including the sea trial framework.
• The re-establishment-of-power procedure after an emergency override.

The resolution applies to ships choosing EPL as their compliance method. It does not mandate EPL; ShaPoLi and technical measures are equally valid alternatives under Reg.25.

Resolution MEPC.357(78): ShaPoLi guidelines

MEPC.357(78), adopted at MEPC 78 on 10 June 2022, provides the parallel guidelines for Shaft Power Limitation. Key provisions:

• Technical specification of the shaft power monitoring system: a calibrated torque meter or strain gauge with continuous power calculation.
• Accuracy requirements: within 2% of full scale in service (calibrated to within 1% at installation).
• Alarm threshold: set at a value such that sustained operation above the limited MCR triggers immediate audible and visual alarm.
• Intervention within 10 seconds of alarm: automatic throttle reduction for electronically governed engines, or manual response with logged confirmation for mechanically governed engines.
• Data integrity: tamper-resistant continuous logging at minimum 1-second resolution, retained for at least 12 months.
• Annual OMM review: master documents all unlimited-operation episodes; flag administration receives an annual summary.
• Calibration: full torque-meter recalibration at each drydock survey.

Resolution MEPC.366(79): sea trial verification

MEPC.366(79), adopted at MEPC 79 on 16 December 2022, provides the sea trial methodology used to verify both EPL and ShaPoLi at the initial compliance survey. The trial requires calm water, defined trim and draft, wind speed below Beaufort 5, and the use of calibrated shaft power instrumentation. The measured attained shaft power at limited MCR is compared with the value predicted by the EEXI formula.

Ships that cannot conduct a sea trial (age, commercial constraints, seasonal limitations) may use an alternative verification based on shop-test data and class-approved calculations.

Resolution MEPC.350(78): attained EEXI calculation

MEPC.350(78) is the 2022 Guidelines on the method of calculation of attained EEXI, superseding earlier interim guidelines. It defines the exact calculation procedure: how to account for multiple propulsion lines, auxiliary engines, shaft generators, correction factors for ice class and self-unloaders, and the treatment of waste-heat recovery systems. The old draft of this article incorrectly attributed this function to MEPC.364(79); MEPC.364(79) is a separate resolution on the method of calculation of attained CII, not EEXI.

The MEPC.350(78) calculation feeds directly into the limited-MCR framework. The P_ME,i term in the formula is the 75% of the limited MCR after EPL or ShaPoLi is applied, not 75% of the original installed MCR. This means the attained EEXI calculation as submitted in the EEXI Technical File and verified by the class society is always based on the post-limitation power figure, and any change to the limited MCR (upward or downward) requires a recalculation and recertification. The EEXI attained calculator implements the full MEPC.350(78) procedure including the shaft-generator correction and the auxiliary blower correction.

EEXI Technical File and the Confirmation of Compliance

The EEXI Technical File is the principal certification document under MEPC.351(78). It contains: the SFOC values from the EIAPP Certificate or MEPC.350(78) default tables; the attained EEXI calculation worksheets; the chosen compliance pathway (EPL, ShaPoLi, or technical measures); the limited MCR value in kW; the Onboard Management Manual reference; and, where applicable, the sea trial verification results from MEPC.366(79). The class society issues a Confirmation of Compliance once the Technical File has been reviewed and the sea trial (or alternative verification) accepted. The IEEC endorsement and the Confirmation of Compliance are the two documents a port state control officer will request at a port state control inspection relating to EEXI.

Minimum Propulsion Power: MEPC.232(65) as amended

The principal regulatory floor on EPL and ShaPoLi is the Minimum Propulsion Power requirement of Resolution MEPC.232(65) (the 2013 Interim Guidelines for Determining Minimum Propulsion Power, as amended by MEPC.255(67) and MEPC.262(68)). The minimum power is calculated from the ship’s displacement, breadth, block coefficient, and Beaufort scale wind resistance. It is checked against the limited MCR, not the original MCR. A ship whose limited MCR would fall below the minimum propulsion power cannot use EPL or ShaPoLi to that degree without fleet State approval or an alternative safe-manning measure.

The minimum propulsion power calculator implements the MEPC.232(65) calculation as amended.

Engine Power Limitation (EPL): technical methods

Permanent EPL

A permanent EPL is a physical modification that cannot be reversed without a formal survey and documented recertification. The three main methods under MEPC.335(76):

Fuel rack stop adjustment. A mechanical stop, typically a steel pin or a precision sleeve, is installed in the fuel injection rack to limit the maximum fuel delivery rate. Removal requires documented engine work recorded in the engine logbook and the EEXI Technical File. This method applies to mechanically governed slow-speed and medium-speed diesel engines and is the lowest-cost option, typically below USD 50,000 for a single-engine vessel.

Fuel injector replacement. Nozzle holders with smaller orifice diameters replace the original injectors. The reduced maximum injection rate limits peak MCR. Each injector replacement is recorded in the EIAPP Certificate and the EEXI Technical File. This method is used where the fuel rack mechanism cannot accommodate a physical stop without redesign.

Engine control system hard limit (firmware lock). The engine management system maximum output setpoint is reduced and the configuration locked by the engine manufacturer or a class-approved service provider. Reversal requires authorised intervention. This is the dominant method on electronically controlled engines (e.g., MAN B&W ME series, Wartsila RT-flex), where the change is a validated parameter adjustment rather than a mechanical alteration.

Permanent EPL is operationally simple. Once installed, the engine will not exceed the limited MCR even under full-throttle demand. The limitation has no moving parts to fail in service. The downside is that emergency situations requiring full engine output cannot be met without the formal unsealing procedure.

Sealable EPL

A sealable EPL limits the engine in normal operation but allows a controlled override in defined emergencies. MEPC.335(76) requires the sealable arrangement to incorporate a tamper-evident seal so that any override is recorded and verifiable at survey.

Software limit with wire seal. The engine control system maximum output setpoint is reduced. A wire seal with a unique identifier is applied to the control panel or junction box housing the override parameter. Breaking the seal during an emergency override is logged automatically in the electronic engine log, and a replacement seal is applied at the next scheduled engine work.

Mechanical limit with seal. A mechanical stop is physically locked in place by a wire seal. The unsealing procedure requires two-person authorisation (master and chief engineer as a minimum), a written entry in the engine logbook, and flag-administration reporting on the next annual OMM review.

Sealable EPL is more common than permanent EPL on ships operating in trade lanes where emergency full-power requirements are foreseeable. The BIMCO EEXI Clause for Time Charters (May 2022) specifically addresses the allocation of costs and consequences when the charterer requests an emergency unsealing.

Reserve power and emergency override

MEPC.335(76) permits override of a sealable EPL for the following documented emergencies:

• Severe weather: Beaufort 8 or above, where the ship needs full power to maintain heading and avoid beam-on sea conditions.
• Collision avoidance: COLREGs Rule 8 (action to avoid collision) and Rule 17 (action by the give-way and stand-on vessel).
• Search and rescue: SAR operations under the IAMSAR Manual.
• Rendering assistance to vessels in distress: SOLAS Chapter V, Regulation 33.
• Towage operations required for safety.

Each override event is documented in: the engine logbook (immediate entry by the duty engineer); the OMM (annual review entry by the master); and the flag-administration annual report. If there are multiple unsealing events in a survey period, the IEEC endorsement at next renewal survey records the summary.

The re-establishment-of-power procedure requires fitting a new seal after the emergency ends and confirming the engine control system is back at the limited setpoint before the vessel resumes commercial service.

EPL verification

At the initial compliance survey, EPL verification requires: documentation of the method (permanent or sealable, mechanical or software); sea trial verification under MEPC.366(79) confirming the attained shaft power at limited MCR; class approval of the OMM; and IEEC endorsement recording the limited MCR value in kW.

At annual surveys, the verifier confirms: for sealable EPL, the wire seal is intact and matches the record; for software EPL, the control system configuration remains at the approved setpoint; all override events are documented; and the OMM is current. The MARPOL Annex VI survey calculator and IAPP certificate calculator implement the survey cycle verification.

Shaft Power Limitation (ShaPoLi): technical methods

Shaft power monitoring system

ShaPoLi requires a continuous shaft power measurement system meeting MEPC.357(78) accuracy standards. The system has four components:

Torque meter. A calibrated strain-gauge or magnetoelastic torque sensor bonded to or clamped around the propeller shaft. The strain-gauge type uses a Wheatstone bridge with slip rings or telemetry to read torsional strain; the magnetoelastic type uses the change in magnetic permeability of the shaft material under torsion. Both types achieve the required accuracy of within 1% at calibration and within 2% in service. Installation requires shaft inspection and, for bonded types, surface preparation. Typical installation cost: USD 80,000-200,000 per shaft.

Shaft speed sensor. A magnetic pickup or optical encoder measuring shaft RPM. Combined with the torque measurement, this provides instantaneous shaft power: P = M × 2π × n, where M is torque in kNm and n is shaft speed in revolutions per second.

Power monitoring unit. An electronic unit computing the continuous shaft power from the torque and speed signals, displaying the value on a bridge panel and an engine-control-room panel, and logging it at 1-second intervals to tamper-resistant storage.

Data management system. Stores the continuous shaft power record for at least 12 months, allows authorised download for survey verification, and is sealed against unauthorised modification.

Alarm and intervention procedure

When measured shaft power exceeds the limited MCR value, MEPC.357(78) requires:

1. An immediate audible and visual alarm on the bridge and in the engine control room.
2. Automatic throttle reduction within 10 seconds for electronically governed engines. Mechanically governed engines require a manual throttle reduction with confirmation logged in the monitoring unit.
3. An event log entry capturing: timestamp, attained power at alarm trigger, limited MCR value, duration of overage, and operator response (automatic or manual).

The alarm threshold is typically set 5% above the limited MCR value to allow for torque-meter measurement uncertainty and brief wave-induced load transients, avoiding nuisance alarms from short-duration spikes that would not constitute a regulatory exceedance.

Unlimited operation in emergencies

ShaPoLi is operationally more flexible than EPL for emergency situations. The OMM specifies pre-approved scenarios in which the shaft power limit may be exceeded temporarily:

• Severe weather (Beaufort 8 or above).
• Collision avoidance.
• Search and rescue.
• Towage and vessel-in-distress assistance.
• Other safety-critical situations identified and documented by the master in the OMM.

Each unlimited-operation event is recorded automatically by the shaft power monitoring system (timestamp, peak power, duration) and manually by the duty engineer in the engine logbook. The annual OMM review by the master compiles a summary of all unlimited-operation events. Sustained unlimited operation, defined in MEPC.357(78) as continuous operation above the alarm threshold for more than 5 minutes, triggers a formal flag-administration report within 30 days.

ShaPoLi and the fuel-side audit

The shaft power record provides a real-time energy audit that is independent of the bunker delivery note (BDN) system. Where the shaft power record and the BDN fuel-consumption record diverge beyond the expected measurement tolerance, the discrepancy is flagged at annual survey as a potential data integrity issue. The BDN reconciliation calculator implements the parallel fuel-side check that port state control surveyors use to cross-check the shaft power data.

ShaPoLi verification

At the initial survey: calibration certificate for the torque meter (traceable to a national standards laboratory); sea trial under MEPC.366(79); class approval of the OMM and alarm threshold; and IEEC endorsement. At each annual survey: torque-meter calibration current (full recalibration at drydock); shaft power records intact and exportable; unlimited-operation events documented; and OMM current.

Calculation of the required MCR limitation

EEXI as a function of MCR

The attained EEXI is approximately proportional to the two-thirds power of MCR at constant specific fuel oil consumption, capacity, and hull form. For a single main engine on the standard 75% reference speed, the relationship is:

The two-thirds exponent combines the cubic speed-power law (P ∝ v³) with the linear power-to-CO2 relationship at constant specific fuel oil consumption.

Required limited MCR

Rearranging for the limited MCR needed to reach a target EEXI value:

The EPL required MCR reduction calculator implements this for both single-engine and multi-engine arrangements and returns the required limited MCR in kW, the percentage reduction from original MCR, and the estimated speed loss using the cubic-law approximation.

Three worked examples

50,000 DWT bulk carrier. Original attained EEXI: 5.0 g CO2/(t·nm). Required EEXI: 4.2 g CO2/(t·nm). Original MCR: 7,500 kW.

MCR_limited = 7,500 × (4.2 / 5.0)^(3/2) = 7,500 × 0.770 = 5,775 kW

This is a 23% MCR reduction. The cubic-law speed loss: v_limited / v_original = (0.770)^(1/3) = 0.916, so a ship doing 14.5 knots at original MCR would be limited to about 13.3 knots. That 1.2-knot loss costs approximately one additional round voyage per year on a 10,000 nm trade.

12,000 TEU container ship. Original attained EEXI: 13.0 g CO2/(t·nm). Required EEXI: 11.0 g CO2/(t·nm). Original MCR: 60,000 kW.

MCR_limited = 60,000 × (11.0 / 13.0)^(3/2) = 60,000 × 0.778 = 46,680 kW

A 22% MCR reduction. At 22.5 knots original, the limited speed is about 20.8 knots. On a round-the-world liner service with weekly calls, a 1.7-knot loss requires either a schedule adjustment or an additional vessel in the string.

LR1 product tanker. Original attained EEXI: 7.5 g CO2/(t·nm). Required EEXI: 6.0 g CO2/(t·nm). Original MCR: 12,500 kW.

MCR_limited = 12,500 × (6.0 / 7.5)^(3/2) = 12,500 × 0.716 = 8,944 kW

A 28% MCR reduction and an estimated 11% speed loss, from about 15.5 knots to 13.8 knots. Tanker operations are typically less speed-sensitive than container services, but the 1.7-knot loss may affect Worldscale freight calculation for time-sensitive cargoes.

EPL vs ShaPoLi: comparison

The remaining 30% of EEXI compliance fleet-wide was achieved through technical or operational measures without recourse to power limitation: hull cleaning, propeller replacement, engine tuning, energy-saving device installation, and fuel switching.

Operational consequences for the ship

Speed loss and its commercial effect

The cubic speed-power relationship means MCR reductions translate to smaller, but real, speed losses. For a 25% MCR reduction, v_limited / v_original = (0.75)^(1/3) = 0.909, a 9% speed loss. For a 30% reduction, the loss is 11%. For a 40% reduction, 16%.

On a bulk carrier typically operating well below MCR for fuel-economy reasons, the EPL ceiling rarely constrains normal voyaging. The commercial impact falls on port-to-port passage time in strong adverse current (e.g., northbound on the Humboldt Current, westbound in the Roaring Forties), where the extra reserve power would previously have allowed speed maintenance that is no longer available.

On a container ship with a fixed weekly-port-call schedule, a 1.5-2.0 knot speed loss may require schedule adjustment, additional tonnage in the string, or renegotiation of charter party speed warranties. This drove the higher ShaPoLi adoption among container operators: ShaPoLi allows full-power operation when schedule recovery genuinely demands it, subject to the OMM logging requirement.

Bollard pull and manoeuvring

Limited MCR reduces available power for harbour manoeuvring and towage. Bollard pull scales approximately with MCR^(2/3), so a 25% MCR reduction reduces bollard pull by about 17%. For ships that use their own propulsion power during port entry (rather than relying entirely on tugs), this may require additional tug assistance, affecting port call costs.

Offshore vessels (platform supply, anchor handling) are generally exempt from EEXI power limitation because they fall under the alternative-compliance provisions for ships of special construction, or their size puts them below the applicable EEXI threshold.

Heavy weather reserve power

MEPC.332(76) (the guidelines on minimum propulsion power, adopted alongside MEPC.328(76)) establishes the policy context: a ship with a limited MCR that approaches the minimum propulsion power level requires enhanced weather routing and, where necessary, uses the emergency override to access full power when sea state demands it. Flag administrations including the Bahamas Maritime Authority and the Marshall Islands Registry have issued specific guidance requiring OMM weather-routing sections for ships where the limited MCR is within 15% of the minimum propulsion power.

Cargo loading restrictions

Some dry-bulk cargoes requiring continuous operation of cargo-handling gear (cement discharge by compressed air, iron ore concentrate with high slump risk) impose an operational profile that historically required brief full-power episodes during cargo operations. Where EPL limits preclude this, operators have either shifted to ShaPoLi (which accommodates the operational case in the OMM) or restricted the cargo grades accepted. No IMO guidance specifically addresses this interface; it is handled through the ship’s Safety Management System under ISM Code.

Charter-party considerations

BIMCO EEXI Clause for Time Charters

The BIMCO EEXI Clause for Time Charters, published May 2022, addresses the mismatch between the regulatory obligation (which falls on the shipowner as ISM manager) and the commercial consequence (which falls on the charterer as operator). The clause requires:

• Owner disclosure of the limited MCR and resulting speed warranty before fixing.
• Allocation of unsealing costs and consequences: the charterer pays for the additional fuel consumed during any unsealing episode requested for commercial, rather than safety, reasons.
• A charterer-notice procedure for anticipated commercial unsealing (e.g., schedule-recovery sprint), requiring master consent and formal OMM documentation.

The clause is now standard in the major bulk carrier and tanker time-charter markets. The parallel BIMCO CII Clause addresses CII management under Regulation 28, and the BIMCO EU ETS Clause addresses EU ETS for shipping cost allocation.

Speed warranty under an EPL or ShaPoLi ship

A conventional time-charter speed warranty (“vessel performs approximately X knots on Y tonnes per day in good weather”) is now typically structured as a limited-MCR warranty:

• A base speed warranty at the limited MCR.
• A maximum speed warranty at the original MCR for emergency unsealing only, with specified fuel-consumption assumptions.
• A performance-claims procedure that assesses speed performance against the limited MCR operating envelope, not the original hull-speed envelope.

LMAA arbitrators in 2023 and 2024 awards consistently held that the limited MCR is the operative reference for performance claims post-EEXI. Original MCR is relevant only for emergency use documented in the OMM.

Voyage charter considerations

In voyage charters, the laycan and estimated time of arrival (ETA) are typically based on the limited-MCR speed. If a vessel unseals EPL to make an ETA, the additional fuel cost falls on the owner under most standard charter forms (GENCON, BPVOY5, Shellvoy 6) unless the charter party has been amended to incorporate the BIMCO EEXI Clause or an equivalent.

EEXI, EPL/ShaPoLi, and CII interaction

EEXI under Reg.25 is a one-time design-index check: once the IEEC endorsement is issued with the limited MCR on record, no further EEXI compliance action is required for that ship (absent a major conversion that triggers re-certification). The continuous compliance burden is CII under Regulation 28, which rates the ship’s actual operational carbon intensity A to E on an annual basis based on fuel consumption and cargo-distance work reported through the IMO Data Collection System (DCS).

EPL and ShaPoLi interact with CII in two ways. First, a lower limited MCR ceiling reduces the maximum fuel-burn rate that the ship can sustain, which lowers the upper bound of potential CII deterioration from high-speed operation. A ship capped at 75% of its original MCR cannot, even with full-throttle demand from the charterer, run at the original high-speed fuel profile. Second, the speed reduction induced by the limited MCR often aligns with the slow steaming strategy that many operators already used before EEXI, so the CII impact of EPL may be modest on ships that habitually operated at 60-70% of original MCR for commercial reasons before the regulation came into force.

The 2024 IMO MEPC session noted the complementarity between EEXI and CII and confirmed that no double-counting of emission reductions is required in the IMO DCS annual reporting: the EEXI Technical File and the SEEMP Part III CII plan are separate documents serving different regulatory functions.

Where a ship has a D or E CII rating for three consecutive years, Regulation 28 requires a corrective action plan. If the ship already has EPL or ShaPoLi in place, the corrective action plan typically focuses on operational measures (speed reduction, weather routing, hull maintenance, fuel quality optimisation) rather than further power limitation, because the power-limitation mechanism has already set the design-index floor. The CII 3-year corrective plan calculator models the trajectory to a C rating from a D or E starting point, accounting for the limited MCR as the speed ceiling.

One documented interaction: a ship with sealable EPL that unseals frequently to meet charterer demands will record all of that high-speed consumption in its annual CII. If the unsealing frequency is high enough, the ship may achieve EEXI compliance but fail the CII rating in the same year. This creates a direct commercial tension between the shipowner’s EEXI obligation and the charterer’s operational demand, which the BIMCO EEXI Clause addresses through cost allocation but does not resolve at the CII level.

Industry adoption patterns

The 2024 DNV Maritime Forecast and Lloyd’s Register EEXI Compliance Pathways survey (2024) provide the most detailed published breakdown by ship type:

Bulk carriers. Around 80% of EEXI-compliant bulk carriers used EPL, 5% used ShaPoLi, and 15% used technical measures alone. The stable operating profile of dry-bulk voyaging, with predictable trade routes and long laden passages, makes EPL the simpler and cheaper solution. The low ShaPoLi adoption reflects the additional calibration burden relative to the operational flexibility gain.

Tankers. Around 70% EPL, 10% ShaPoLi, 20% technical measures. The pattern is similar to bulk carriers, with slightly higher technical-measure adoption reflecting the higher cargo value and the importance of full engine power during cargo-pump operations in some tanker types.

Container ships. Around 30% EPL, 40% ShaPoLi, 30% technical measures. The higher ShaPoLi adoption reflects the variable operating profile of liner services, where different legs of a rotation are sailed at different speeds, and the commercial pressure to maintain schedule with occasional full-power sprints.

Cruise vessels. Around 20% EPL, 50% ShaPoLi, 30% technical measures (often combined with shore-power retrofits and hotel-load efficiency measures). Itinerary flexibility and the high cost of schedule disruption drive ShaPoLi preference.

LNG carriers. Around 25% EPL, 25% ShaPoLi, 50% technical measures. The high technical-measures adoption reflects the favourable EEDI baseline of LNG-fuelled propulsion and the additional flexibility available through boil-off gas management and low-pressure gas mode operation.

Critical assessment: real CO2 reductions vs. paper compliance

The principal criticism of the EPL/ShaPoLi mechanism is that it permits paper compliance without a mandatory change in operational behaviour. A ship operating the same actual shaft power as before the limitation (because it habitually ran well below MCR) achieves the same actual CO2 emissions. The Required EEXI is met because the design speed in the EEXI formula was recalculated for the lower limited MCR, not because the ship actually burns less fuel.

The IMO acknowledged this in MEPC.328(76) Annex 9 (the impact assessment) and concluded that three secondary pathways would convert paper compliance to real reductions:

First, commercial pressure: time-charter speed warranties anchored to the limited MCR create a market incentive to operate at or below the new ceiling. Second, the CII rating: a ship that operates above the limited MCR via unsealing accrues that fuel consumption in its annual CII, and repeated D or E CII ratings trigger mandatory corrective action under Regulation 28. Third, fuel price: the bunker price signal already drove slow steaming before EEXI; the power ceiling reinforces the same direction.

A 2024 DNV survey of 200 ships subject to EEXI found an average actual CO2 reduction of 8% from EEXI compliance, against a theoretical (paper) reduction of 22% from the EEXI formula. The gap is explained by two factors: ships that already operated well below original MCR for commercial reasons gained little from the power limitation ceiling; and unsealing events on ships with sealable EPL partially eroded the theoretical reduction.

2026 regulatory context: short-term measures review and the GHG pricing direction

The IMO’s short-term GHG measures, including EEXI under Reg.25 and CII under Reg.28, were adopted as a package in 2021 with a built-in review mandate. MEPC 80 (July 2023) reviewed the initial CII implementation and tightened the reduction-factor trajectory for 2026-2030. The EEXI mechanism itself was not modified at MEPC 80 or MEPC 81, but the mid-term and long-term measures framework advanced at a special MEPC session in April 2025, with adoption in principle of GHG pricing and a fuel standard.

The IMO adopted in principle a GHG pricing and fuel standard framework (the Marine Fuel Standard (GFS) and a levy on GHG-equivalent emissions) at a special MEPC session in April 2025. This framework, if adopted as regulation, would enter force no earlier than 2027 and would operate alongside, not instead of, EEXI and CII. The EEXI/EPL/ShaPoLi baseline remains the operative compliance check for existing ships until at least the end of the current EEXI review cycle.

MEPC 86 (expected late 2026 or early 2027) is scheduled to review the EPL and ShaPoLi guidelines, including potential tightening of data integrity requirements for ShaPoLi shaft power records and potential extension of EEXI to cover ship types currently excluded (fishing vessels, government vessels, ships below 400 GT on international voyages). The 2026 position is that no formal proposal to amend MEPC.335(76) or MEPC.357(78) has been circulated.

Limitations

EPL and ShaPoLi address the attained EEXI at the design-index level. They do not guarantee real operational CO2 reductions: a ship with sealable EPL that unseals frequently can emit as much as a non-limited ship. The mechanisms do not address auxiliary engine emissions, hotel load, cargo refrigeration, or port waiting time, all of which can be material contributors to the annual CII rating.

The EEXI formula uses a fixed reference speed (75% of limited MCR) that does not represent the actual operational speed profile of most tramp ships, which routinely operate at 60-70% MCR or below for commercial reasons. This means the EEXI calculation is a proxy index rather than an actual efficiency measurement, and a ship can have a compliant attained EEXI while emitting more CO2 per tonne-mile than a non-compliant ship operating at a more efficient point on its propulsion curve.

ShaPoLi calibration requirements create a maintenance burden that some flag states have found difficult to enforce in remote drydock locations. The MEPC.357(78) requirement for traceable calibration at each drydock survey is not consistently applied across all flag administrations and class societies, and the IMO Secretariat flagged this as a data quality concern at MEPC 81.

The attained EEXI formula per MEPC.350(78) uses SFOC values from the EIAPP Certificate, which were measured at engine shop test under full-load conditions. In service, an aged engine typically has higher SFOC than the shop-test value, meaning the attained EEXI in service is higher than the certified value. This gap is not reflected in the current EEXI framework, which uses the shop-test SFOC throughout the ship’s life.

EPL and ShaPoLi apply to main propulsion engines. They have no bearing on vessel GHG emissions from generators, boilers, incinerators, or refrigerant leakage. Ships meeting the Required EEXI through EPL while running inefficient auxiliary plant may have a net environmental performance worse than a ship with a slightly higher attained EEXI but efficient auxiliary systems.

See also

• What is EEXI - the parent index that EPL and ShaPoLi support
• What is EEDI - the design-phase index for new ships
• What is CII - the annual operational carbon intensity indicator
• SEEMP I, II and III - the ship energy efficiency management plan
• MARPOL Annex VI - the parent regulation
• IMO GHG Strategy - the policy framework
• IMO Net-Zero Framework - the developing post-2030 framework
• Slow steaming and CII - the operational complement to EEXI
• EU ETS for shipping - the parallel regional regime
• Marine diesel engine - the engine technology subject to EPL
• Specific fuel oil consumption - the engine efficiency metric central to EEXI
• COLREGs Convention - emergency manoeuvring rules
• SOLAS Convention - distress and safety obligations
• Classification society - Recognised Organisations approving EPL/ShaPoLi
• Flag state and flag of convenience - flag-state EEXI verification
• Port state control - enforcement mechanism
• Engine sea trial procedures - sea trial verification context

Related calculators

• EEXI Attained Calculator - the EEXI as-built calculation
• EEXI Required Calculator - the regulation-driven Required EEXI
• EPL Required MCR Reduction Calculator - sizes the limited MCR for a target attained EEXI
• EPL Calculator (MEPC.328(76)) - engine power limitation calculation
• ShaPoLi Calculator - shaft power limitation calculation
• Engine Cube-Law Fuel Calculator - speed-fuel relationship
• Minimum Propulsion Power Calculator - MEPC.232(65) floor check
• MARPOL Annex VI Survey Calculator - Annex VI survey cycle
• IAPP Certificate Calculator - IAPP issue and endorsement
• MARPOL EEXI Required Calculator - regulation-anchored Required EEXI
• CII Attained Calculator - operational CII calculation
• CII Required Calculator - regulation-driven Required CII
• BDN Reconciliation Calculator - on-board fuel reconciliation
• GFI Attained Calculator - WtW intensity from fuel mix
• GFI Compliance Calculator - Net-Zero Framework compliance
• IMO DCS Annual Fuel Report Calculator - annual fuel-consumption report
• SFOC Sensitivity to Air Temperature Calculator - engine performance correction