Hydrofoils are wing-shaped submerged structures designed to lift a vessel's hull above the water's free surface during motion, thereby reducing hydrodynamic drag and increasing efficiency. This advanced technology is widely employed in marine engineering to improve speed and reduce fuel consumption. Analysing hydrofoil dynamics requires considering the interaction with both surrounding fluids, namely water and air. While air resistance is often neglected in practical applications due to its minimal contribution to overall drag in stable operating conditions, it can significantly influence the system in transient scenarios such as abrupt changes of angle of attack or gusty wind conditions. The present investigation focuses on a 3D numerical comparative analysis of two approaches to fluid-structure interaction: a two-fluid model incorporating both air and water and a simplified one-fluid model considering water alone. This comparison is carried out for both static and dynamic scenarios to quantify the influence of air on the overall fluid-structure interaction and assess the validity of the simplified model under various conditions. Within this framework, a partitioned approach is employed to address the fluid-structure interaction problem. The coupling at the interface between the fluid and the structure is managed using quasi-Newton schemes, which are specifically designed to enhance computational efficiency. These schemes reduce the number of iterations required to achieve convergence by approximating the Jacobian matrix more efficiently. Additionally, hydrofoils are modelled using advanced composite material to improve their strength and to enhance their lightweight properties. By evaluating the performance and accuracy of the two-fluid and one-fluid models, the study aims to provide insights into the conditions under which air-fluid interactions significantly impact structural behaviour and determine conditions under which the one-fluid approximation provides reliable results while optimising computational resources.