Evaluation of wave loads on a ship translating in water waves is of practical importance in ship hydrodynamics, because it is paramount to the design of ship hull structures and provides essential inputs for ship maneuvering analysis. The linear radiation and diffraction of water waves by a translating ship is studied in this paper. A time-domain Rankine panel method is developed in a non-inertial body-fixed coordinate system, which is able to consider large-amplitude horizontal motions consistently. The double-body flow is used as the basic steady flow model. To ensure numerical stability, an implicit Euler scheme is adopted for time marching, and horizontal derivatives on the free surface are calculated using an upwind-biased finite difference scheme. Numerical examples in comparison with experimental measurements are exhibited to demonstrate the validity of the developed solver.