This paper is concerned with the development and application of hydrodynamic theory required for the prediction of wave drift damping phenomena as introduced by Wichers in 1979 and 1982, ref.  and . The concept of wave drift damping necessitates the development of forward speed dependent expressions for the mean wave drift forces and a new 3-D diffraction potential algorithm for forward speed (Wichers and Huijsmans  and Hearn and Koon ). In this paper computed mean wave drift forces are validated with results from model tests as reported by Wichers . Results will be discussed of model tests and computations for this tanker in irregular waves with and without current.