It is necessary to predict ship response to waves already during the design phase. It affects the ship's ability to achieve and maintain speed, the necessary power and fuel consumption. In order to have good seakeeping characteristics of ship, motion amplitudes and accelerations must be within acceptable limits, and added resistance in waves should not have significant affect on the decrease in ship speed. In this paper the response of the ship in regular bow waves was calculated. The ship response was calculated at defined sea states in certain frequency range and at different forward speeds. Calculations were conducted using software package HydroSTAR (Bureau Veritas). Since after maritime accident damaged ship should be often removed from the place where accident occurred, seakeeping characteristics of damaged ship were also calculated. The damage was simulated using two models: as an increase of ship displacement mass and as flooded tank within midship area. In addition to the ship response to waves, the added resistance of ship in waves was calculated. Calculations are based on linear potential flow theory, and added resistance was determined by the wave drift force as the second order wave load. Quadratic transfer function QTF which describes low-frequency second order wave loads was approximated by its zeroth term only, i.e. by the drift load at incoming wave frequencies. Response amplitudes of the ship were presented using transfer functions. Seakeeping characteristics of the intact and damaged ship were compared. The calculation results show that response amplitudes of the damaged ship with flooded tank differ slightly from the response amplitudes of the damaged ship with increased displacement.