Energy Efficiency Design Index

The Energy Efficiency Design Index was the IMO's first mandatory technical measure aimed at reducing carbon emissions from shipping, and it applies at the point a ship is designed and built. It expresses a ship's efficiency as the grams of carbon dioxide emitted to carry one tonne of cargo one nautical mile under defined conditions, calculated from the ship's engine power, fuel, capacity and reference speed. Each new ship must achieve an attained EEDI at or below a required value for its type and size, so the index effectively sets a minimum efficiency for new construction.

The power of the EEDI lies in the way the required value tightens over time in successive phases. As each phase takes effect the permitted emissions per unit of transport work are reduced, so shipbuilders and designers must deliver progressively more efficient vessels — through more efficient hull forms, propulsion and machinery, waste-heat recovery, and in some cases alternative fuels, rather than repeating older designs. This creates a long-term ratchet that steadily improves the efficiency of the fleet as old ships are replaced by new ones built to the standard.

The EEDI is the design counterpart to the other efficiency instruments. Because it applies only to new ships, the EEXI was later introduced to bring existing ships up to a comparable design standard, while the operational CII rates how efficiently any ship is actually run each year. Together these measures form the technical and operational backbone of the IMO's programme to reduce greenhouse-gas emissions from international shipping. For naval architects and shipowners, the EEDI has been a major driver of innovation, encouraging designs optimised for fuel efficiency and lower emissions rather than for maximum speed, and it continues to influence the specification of every new merchant ship.