A Comparative Study of the Energy Efficiency of Hydrofoil Vessels and Slender Catamarans

The transition to zero-emission energy systems introduces new challenges in fast ferry design, particularly in relation to the increased weight and cost associated with stored and consumed energy. Hydrofoils may address these challenges by reducing the energy consumption and increasing the operational range. This study compares the energy efficiency of hydrofoiling fast ferries to that of conventional slender catamarans across a range of vessel sizes and design speeds. To achieve this, a set of recently developed vessel designs and simulation models are employed to estimate vessel resistance. The Lift-to-Drag ratio (L/D ratio) is used for fair comparison and generalization. The study finds that the L/D ratio of optimized hydrofoil vessels increases slightly with speed up to an optimum design speed, after which it drops due to the increased importance of strut resistance and wing loading constraints posed by cavitation. The optimum design speed varies with vessel size, from approximately 28 knots to approximately 33 knots for design masses from 26 tonnes to 141 tonnes, respectively. In contrast, the L/D ratio of conventional catamarans operating at service speed is approximately proportional to U−32. A benefit of scale was identified for both vessel types. Hydrofoil vessels offer greater advantages as the design speed increases or the vessel mass decreases. For vessels weighing 78 tonnes and 141 tonnes, the critical speeds for achieving net energy savings were determined to be approximately 25 knots and 27 knots, respectively. Opting for a hydrofoil design instead of a slender catamaran can result in energy savings of more than 54 % within the investigated speed and mass ranges. Furthermore, the study presents a breakdown of the key resistance components of hydrofoil vessels, indicating that up to 54 % of the overall resistance originates from air resistance and struts-related resistance components within the investigated design parameter ranges.