EEXI compliance and CII performance in existing container ships: Implications for propeller retrofit

Abstract

This study assessed the EEXI, CII implementation and propeller retrofits as the decarbonization measures for existing container ships, focusing on actual CO₂ emissions reduction. EEXI compliance across the fleet relied mainly on engine power limitation measures such as EPL/ShaPoLi, delivering an average calculated CO₂ reduction of about 17.3%, while the average calculated vessel speed dropped by approximately 10%. In contrast, the actual CO₂ reduction based on DCS data for CII calculation was about 33.6%, and ship speed was reduced by about 39%. This reflects a compliance pathway driven primarily by the operational and technical measures proposed under IMO regulations. This study found that propeller retrofits reduced the required shaft power without sacrificing vessel speed, leading to fuel savings and improved operational carbon intensity. These advantages were most evident in high-power vessels above the 6,000 TEU class. The deterioration in the ship's CII rating slowed after the propeller retrofit. However, this measure is not suitable for all ships, and CII requirements are becoming increasingly stringent. Therefore, propeller retrofit should be considered an interim measure for existing container ships while more fundamental decarbonization solutions are being developed.