Let's assume you have a car, Maruti swift
The company claims that the car will get 20 km/L mileage.
And that exhaust emission of the car will be with in the legal limit.
This is EEDI
Energy Efficiency Design Index.
That means RTO rules says cars of a certain segment and certain engine power shall not produce CO2 and other gases more than the legal limit.
Main Idea of this rule is to use more efficient and less polluting engine while manufacturing the cars.
So govt has set an index for each type of vehicle.
This rule will be stricken over a period of time ( B4 engine to B6 engines)
Similarly, for ships IMO has set an index for CO2 emission limit.
2013 to 2015 Phase Zero
2015 to 2020 Phase I - CO2 emission will be reduced by 10%
2020 to 2025 Phase II- CO2 emission will be reduced by 20%
2025 to 2030 Phase III- CO2 emission will be reduced by 30%
when ships are constructed machinery is designed to get maximum energy efficiency and less emission.
So during the design stage of shipbuilding naval architects sets limits for CO2 emission per tone mile depending upon the size of ships.
Then calculate how much energy(fuel) is required to produce a certain amount of power in loaded and ballast conditions. To obtain the optimal use of the energy they will consider hydrodynamics, windage resistance, underwater resistance, so that power consumption and CO2 emission remain within the limit.
let's go back to the car again.
But we all know we don't get that much mileage because of our road condition, traffic, and some time we play fast and furious in empty roads. Over a period of time when we go and check the emission value, it will increase significantly.
Similarly, ships will not get EEDI value all the time. due to rough weather, running at over speed to maintain ETA, Delays in operations.
When Cheif engineer calculates monthly fuel consumption in relation to distance covered or the operations carried out by the ship, the energy consumption per nautical mile and CO2 emission per tone of cargo carried, It may overshoot above the average the value.
So there must be some guidance procedure for assisting the ship's management team for maintaining the fuel consumption within the limit. This is called EEOI,
Energy Efficiency Operation Index.
This helps the staff of the ship to reduce the wastage of energy.
Like powering down generators when not required and less fuel will be burned and less emission.
Auto start of Generators when more power is demanded.
Using the main engine at economical RPM.
Proper weather routing will help to minimize power consumption.
For cargo discharge operation use min required Pumps and power packs.
PLS READ CAPT RAJEEV JASSAL'S BLOG FOR MORE KNOWLEDGE