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1 Polish Maritime Research

1 2025

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Drag Reduction and EEXI Compliance: Evaluating Air Lubrication for In-Service Ships via CFD

Abbas Nawar, Hawa Rami, Hatem Wehad

Polish Maritime Research

2025

nr 4

59--77

This research used CFD techniques to study the effect of air lubrication technology on the Energy Efficiency Existing Ship Index (EEXI), developed by the International Maritime Organization. The Unsteady RANS (Reynolds-Averaged Navier-Stokes Equation) and the k-ω SST turbulence model were used to solve the Navier-Stokes equations governing flows, while the Volume of Fluid (VOF) method was used to solve the two-phase (air-water) flow. The JBC bulk carrier was chosen for this study because its shape closely resembles that of bulk carriers and tankers currently operating in the merchant fleet. Initially, the ship model was studied alone, without any appendages, at a scale of 1:40. The MP687 propeller was used with this ship in a self-propulsion test. An Open Water Test was conducted, with the Verification and Validation procedure being applied to the CFD results obtained for the JBC alone, in order to verify the accuracy of the numerical grid and the equations and turbulence models used to complete these calculations. The wave effect and ship motions (pitch, heave, roll, etc.) were neglected and the calculations were carried out in calm water. Then, air flow directing strakes were added to the bottom of the parallel body of the ship to investigate the impact of air lubrication on the EEXI value. At this stage, air lubrication was used for the ship alone, without a propeller, and then again for the ship with a propeller. Several types of air flow-directing strakes were tested, to trap air beneath the parallel body of the hull. The implementation of air lubrication technology with the proposed strakes reduced total ship resistance, resulting in a 16.67% improvement in the attained EEXI value. This reduction directly correlates with lower CO₂ emissions per unit of transport work (measured in grams of CO₂ per ton × nautical mile), demonstrating the system’s potential to enhance compliance with IMO’s carbon intensity regulations, without compromising operational performance.