  It is shown how to model weakly dissipative free-surface flows using the
classical potential flow approach. The Helmholtz-Leray decomposition is applied
to the linearized 3D Navier-Stokes equations. The governing equations are
treated using Fourier--Laplace transforms. We show how to express the vortical
component of the velocity only in terms of the potential and free-surface
elevation. A new predominant nonlocal viscous term is derived in the bottom
kinematic boundary condition. The resulting formulation is simple and does not
involve any correction procedure as in previous viscous potential flow theories
[Joseph2004]. Corresponding long wave model equations are derived.
