The prohibitive computational cost of high-fidelity CFD simulations in marine engineering creates a strong need for efficient Reduced-Order Models (ROMs) during preliminary design. This paper presents the development and validation of a versatile two-dimensional, transient, inviscid panel method for analyzing the hydrodynamics of single and multiple moving foils or cascades. The method, based on a constant-strength source and vortex formulation, solves the potential flow equations and is capable of modeling complex unsteady motions. Its validity is demonstrated through a series of test cases, including a NACA 0012 foil in steady-state, pure pitching, and combined plunging-pitching motions. The results show excellent agreement with experimental, numerical, and Computational Fluid Dynamics (CFD) data for lift-dominated forces, accurately capturing both amplitude and phase. As an inviscid model, it has limitations in predicting drag and thrust. Crucially, the method exhibits significant computational efficiency, with solution times faster than the physical time simulated for typical discretizations, confirming its suitability for integration into rapid design and optimization loops for marine hydrofoils, propellers, and oscillating energy harvesting devices.