Weight of Freight – Navigating IMO 2023

Author Mohsin Parvez - Senior Reporter, Freight & Andrew Khaw - Editor, Asia Freight

The maritime and shipping industry – with more than 50,000 ships on the water – emitted 1.056bn t of CO2 in 2018, about 3pc of total global greenhouse gas (GHG) emissions. The recent Maritime Environment Protection Committee (MEPC) meeting in June 2021 laid down a concrete plan for minimising GHG emissions from ships by 50pc until 2050. According to the MEPC 76 meeting, vessels are required to calculate an Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII) from 2023. What does this mean and what steps should be taken?

Understanding and calculating EEXI

Starting from 2023, each vessel above 400 Gt will require a one-off EEXI calculation to confirm that the vessel meets the energy efficiency design standards. An International Energy Efficiency (IEE) certificate will be awarded if the vessel meets those standards.

Take for instance, a basic 82,000 dwt Kamsarmax vessel with no energy saving devices installed:

Main engine (ME) maximum continuous rating (MCR) 14,280 kw 
ME specific fuel oil consumption (SFOC) 171 gms/kwhr
Auxiliary engine (AE) MCR 5pc of main engine MCR (Assumed as per EEXI guidance)
AE SFOC 187 gms/kwhr
Vessel’s speed on the power speed curve (Vref) 15.09 knots at 75pc MCR
Fuel Constant 3.151
Reduction factor 20
EEDI/EEXI reference line parameters A = 961.79
C = 0.477


 Required EEXI:  [1-(Reduction factor/100)] * [EEXI reference line parameters A*{(Vessel’s DWT)^(minus EEXI reference line parameters C)}]
 (1-(20/100)) * (961.79*((82000)^(-0.477))) = 3.49 grams/ton-mile
 Attained EEXI:  [( pc of MCR * MCR * Fuel Constant * ME SFOC) + (5pc * MCR * Fuel Constant * AE SFOC)] / [DWT * Vref]
 ((0.75*14280*3.151*171)+(0.05*14280*3.151*187))/(82000*15.09) = 5.00 grams/ton-mile

Based on the above calculations, the vessel does not meet EEXI’s requirements, because the attained EEXI (5.00 gms/t-mile) is greater than the required EEXI (3.49 gms/t-mile). So the vessel will have to reduce its MCR to comply with the EEXI regulation, and to attain the IEE Qualification.

 IEE Qualification:  [Required EEXI * (DWT * Vref)-( 5pc * MCR * Fuel Constant * AE SFOC)/(MCR * Fuel Constant * ME SFOC)
 (3.49*(82000*15.09)-(0.05*14280*3.151*187))/(14280*3.151*171) = 0.506 

Based on the calculation above, the vessel can meet compliance standards if the main engine runs at 50.6pc MCR, where the attained EEXI matches the required EEXI. The vessel will be given the IEE certificate, if the main engine’s MCR continues to operate below 51pc and adjusts to the corresponding speed on the power speed curve (13.24 knots in this instance).

The formula to calculate EEXI was derived from the Energy Efficiency Design Index (EEDI). EEDI is applicable to new ships built on or after 1 January 2013. Vessels built on or after 2013, with a valid IEE are not required to calculate EEXI. Some of the variables used in the EEXI formula are listed below:

EEDI/EEXI reference line parameter values:

Ship type A B C
Bulk Carrier 961.79 dwt 0.477
Gas Carrier 1,120 dwt 0.456
Tanker 1,218.8 dwt 0.488
Container ship 174.22 dwt 0.201
LNG carrier 2,253.7 dwt 0.474


 Reference line  = a * b ^ (-c)
 Required EEDI / EEXI  = [1 – (Reduction factor/100)] * Reference line


EEDI reduction factor:

Reduction factors (in percentage) for the EEXI relative to the EEDI reference line
Ship type Ship size Reduction factor
Bulk carrier 200,000 DWT and above 15
20,000 and above but less than 200,000 DWT 20
10,000 and above but less than 20,000 DWT 0-20*
Gas carrier 15,000 DWT and above 30
10,000 and above but less than 15,000 DWT 20
2,000 and above but less than 10,000 DWT 0-20*
Tanker 200,000 DWT and above 15
20,000 and above but less than 200,000 DWT 20
4,000 and above but less than 20,000 DWT 0-20*
Containership 200,000 DWT and above 50
120,000 and above but less than 200,000 DWT 45
80,000 and above but less than 120,000 DWT 35
40,000 and above but less than 80,000 DWT 30
15,000 and above but less than 40,000 DWT 20
10,000 and above but less than 15,000 DWT 0-20*
LNG carrier 10,000 DWT and above 30
*    Reduction factor to be linearly interpolated between the two values dependent upon ship size.
The lower value of the reduction factor is to be applied to the smaller ship size.

Are vessels compliant once EEXI is achieved? What is CII?

The Carbon Intensity Indicator (CII) is a measure of how efficiently a ship transports goods or passengers - linking carbon emissions to vessel capacity and vessel movement. The ship is given an annual rating ranging from A to E. All vessels above 5,000 Gt are required to attain and document an annual operational CII, to be verified against the required annual operational CII, according to the MEPC 76.

The ship is then given an annual rating ranging from A to E, by comparing the attained annual CII of a ship with the direction and distance it deviates from the required CII (DD vector for short).

Ship type Ship size DD vectors (after exponential transformation)
exp(d1) exp(d2) exp(d3) exp(d4)
Bulk carrier dwt 0.86 0.94 1.06 1.18
Gas carrier 65,000 dwt and above dwt 0.79 0.89 1.12 1.36
less than 65,000 dwt dwt 0.85 0.95 1.06 1.25
Tanker dwt 0.82 0.93 1.08 1.27
Container Ship dwt 0.83 0.94 1.07 1.19
LNG carrier 100,000 dwt and above dwt 0.91 0.98 1.05 1.11
less than 100,000 dwt dwt 0.77 0.91 1.12 1.37

Required Carbon Intensity Indicator

Taking the same basic 82,000 dwt Kamsarmax vessel used above:

Average Speed 13.24 knots (basis 50.6pc MCR)
Sailing days 292 days (75pc sailing 25pc at port)
Distance travelled 92,786 nm
Average fuel consumed 32t/day
Fuel Constant 3.151
Sailing days 292 days (75pc sailing 25pc at port)
CII reference line parameters A = 4,977
C = 0.626
2023 CII reduction factor 5pc


Required CII:  [CII reference line parameters A * {DWT^(minus CII reference line Parameter C)}]*[1-(CII reduction factor/100)]
 ((4977*(82000^(-0.626))*(1-(5/100))) = 3.97 grams/ton-mile
CO2 emitted per annum:  Fuel consumed * 1,000,000 (convert tons to grams) * Fuel constant 
 9344*1000000*3.151 = 29,443e^6 grams
Ton-mile:  DWT*Distance sailed 
 82000*92786 = 5,595e^6
Attained CII:  CO2 emitted per annum / ton-mile
 29443e^6/5595e^6 = 3.87 grams/ton-mile
Annual rating:  Attained CII / Required CII compared to DD vector
 3.87/3.97 = 0.97 (C rating)


A basic Kamsarmax with an annual rating of 0.97 is between DD vectors d2 (0.94) and d3 (1.06), and so receives a C rating. The annual rating would be an A for a bulk carrier, if it was at or lower than 0.86 (d1), and B if it was above superior boundary (0.86), but equal to or below the lower boundary (0.94). Vessels that receive A, B, or C ratings, will be issued a statement of compliance. Vessels that receive a D for three consecutive years, or an E rating, will be given a year to develop a corrective action plan that will enable the vessel to achieve at least a C rating. The Statement of Compliance to these vessels will not be issued unless the corrective action plan is reflected in a Ship Energy Efficiency Management Plan (SEEMP) and is verified by the administration or authorised organisations (vessel classification societies).

What are the various ways to implement SEEMP and make a vessel EEXI and CII compliant?

  1. Proper maintenance of the vessel’s hull at dry dock.
  2. Coating the vessel’s hull with good paint to increase hydrodynamic performance.
  3. Improve the vessel’s steering configurations.
  4. Have a more efficient aft-ship, propeller, and rudder arrangements.
  5. Reduce energy consumption in main and auxiliary engines, auxiliary machineries, air conditioning, and other minor energy consumers.
  6. Weather routing and choosing the best route for transportation of cargo.
  7. Using efficient energy saving devices.
  8. Slow steaming of the vessel.
  9. Using of alternative fuels instead of high-sulphur fuel oil or very low-sulphur fuel oil (VLSFO).

As a note, SEEMP plans cannot be applied across a company or fleet-wide, as these plans are ship specific and have to be implemented according to the vessel type, cargoes carried, ship routes, and other relevant factors.

What are the different kinds of alternative fuels available? What are the advantages and disadvantages?

Alternative Fuels Advantages Disadvantages
Liquified Natural Gas
(about 30-40pc more expensive than VLSFO)

  • Easy transition as fuel type is already in use
  • Infrastructure is being developed
  • Has IMO regulations in place
  • Not a long-term solution/alternative
  • Limited CO2 reduction
  • Emits HGH - Methane
    • More potent at trapping heat than CO2
  • Difficult storage requirements
    • Takes up almost twice the space compared to mainstream bunker fuel
    • Needs to be stored at or about -160°c to stay in liquid state
(about 40-120pc more expensive than VLSFO)

  • Does not emit CO2
  • Compatible with current vessel engines
    • Usually blended with mainstream bunker fuels
  • Higher cost compared to mainstream alternatives
  • Limited production capacity
  • Microbes can cause fuel to become a turbid liquid (biofouling)
    • Could cause machinery breakdown

(about 2-20pc cheaper than VLSFO)
  • Easy to store and handle
  • Widely traded
  • Biodegradable and emits low levels of GHG
  • Low cost
  • Higher energy density compared to Ammonia and Hydrogen
  • Limited CO2 reduction
  • Reduced energy density compared to mainstream bunker fuel
  • Low flash point and burns with invisible fire
  • Difficult to handle
    • Toxic
    • Increased corrosion risks
(about 190-270pc more expensive than VLSFO)
  • Does not emit CO2
  • Already produced
  • Green production
  • Practical application and use in the marine industry is present
  • Highly toxic and emits NOx
  • Expensive - costs about three times more than VLSFO
  • Requires refrigeration
  • Reduced energy density compared to mainstream bunker fuel
  • Emits GHG - Nitrous oxide
    • More potent at trapping heat than CO2
  • Little to no infrastructure - no vessels on water
(about 180-270pc more expensive than VLSFO)
  • Does not omit CO2
  • High volumetric density
  • Currently unable to power large vessels
  • Does not exist naturally

Alternative Marine Fuels vs VLSFO




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