Answer
The Energy Efficiency Design Index (EEDI) is a mandatory technical standard under MARPOL Annex VI Chapter 4 that measures a newbuild vessel's structural carbon intensity. Expressed in grams of CO2 per capacity-mile, it evaluates the ratio of environmental cost (CO2 emitted) to transport benefit (capacity × speed):
To comply with progressive IMO reduction targets (Phase 1 through Phase 3/4), technical design adjustments must reduce the calculated numerator (CO2 emissions) or optimize the denominator (capacity-speed product).
To improve EEDI, the aim is:
Attained EEDI≤Required EEDIAttained EEDI≤Required EEDIMain methods are:
- Reduce hull resistance by optimized hull form, bulbous bow, smooth/low-friction coating.
- Improve propeller efficiency using optimized propeller, ducts, pre-swirl devices, rudder bulb, etc.
- Use efficient main engine with lower SFOC and optimized turbocharging.
- Reduce auxiliary power consumption using efficient pumps, fans, VFDs, LED lighting, etc.
- Waste heat recovery to generate electrical power from exhaust gas.
- Use energy-saving technologies such as air lubrication, wind-assisted propulsion and solar power.
- Use lower-carbon fuel, where permitted by the applicable IMO EEDI calculation method.
- Optimize design speed and ship capacity so less power is required per tonne-mile transported.
To improve EEDI we have to reduce the attained EEDI. This can be done mainly by reducing propulsion power through optimized hull and propeller design, selecting a main engine with lower SFOC, reducing auxiliary electrical demand, using lower-carbon fuels, and employing energy-saving technologies such as waste-heat recovery, air lubrication, wind-assisted propulsion and solar power. We can also optimize design speed and increase transport efficiency or capacity. In simple terms, we reduce the CO₂-emission numerator and improve the transport-work denominator.