Operational efficiency optimization method for ship fleet to comply with the carbon intensity indicator (CII) regulation

The Carbon Intensity Indicator (CII) is a regulation issued by the International Maritime Organization to reduce carbon emissions in the shipping industry. However, surveys show that currently 1/3 of ships cannot meet the carbon emission requirements. How to upgrade ship facilities and improve operational efficiency has become a research topic. To overcome it, this study presents an operational efficiency optimization approach for short-term upgrades of the existing fleet. Firstly, the proposed method aims to estimate the annual attained CII of a ship by considering different speed and route choices. Then, an optimization model for the heterogeneous fleet is developed to maximize annual fleet profit while ensuring all ships achieve compliance with CII ratings. The model considers various factors such as ship characteristics, route characteristics, and operational constraints to optimize vessel schedules. Experimental results show that ships operating on specific routes may possess inherent advantages in terms of emission reduction capacity. Moreover, results from the case study reveal that the sample ships require an average speed reduction of 7%, and in some cases, the highest speed reduction could reach up to 20.6%. The proposed method is versatile in dealing with stricter decarbonization regulations to support fleet operational decisions.