In this paper are discussed two possible CFD implementations of the critical wave groups method (CWG). This method shows good promise in addressing the problem of rarity– that is, difficulties in handling extremely low probability values–encountered in simulation-based assessments of ship dynamic stability failure. The focus of the paper is on the accuracy of the waves generated in a numerical wave tank by a) the relaxations zones method; and b) wave making through a paddle. A systematic study of wave elevation error is presented, with reference to the linear and the Stokes 2nd-order wave theories. On the basis of a certain metric, we assess the influence of the spatiotemporal discretization, of the regularity and nonlinearity of the waves, and of the wave generation method. The conclusion of the work is that, CFD wave group generation through a paddle presents a good prospect to be applied for practical dynamic stability assessments.