Heave plates are widely used in floating offshore structures to reduce the heave motion by increasing heave damping and heave added mass, and these parameters are sensitive to the amplitude and frequency of heave motion. It is important to obtain the hydrodynamic parameters, namely, damping and added mass of the floater not only at its natural frequency, which can be obtained from free decay tests but also at other frequencies because the floater response is of interest over a wide range of amplitudes and frequencies. Forced oscillation tests in calm water can aid the investigation of these parameters at various motion frequencies and amplitudes. Heave damping and added mass of classic spar with heave plate are investigated in this study using experiments and numerical simulations of forced heave oscillation of a 1:100 scale model in calm water for various frequency-amplitude combinations. The least square method was used to determine the added mass and damping using three damping models, namely, linear, quadratic, and linear-plus-quadratic, and their applicability assessed. The effect of amplitude and frequency of oscillation on the parameters are discussed for various heave plate configurations with the aid of flow visualization from numerical simulations. Added mass effect is examined using flow visualization of the fluid acceleration field. The scale effect on the parameters is also addressed. © 2021