A Volume of Fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures. The present implementation follows the classic VOF implementation for the liquid-gas system, considering only the liquid phase. Extrapolation algorithms to obtain velocities and pressure in the gas region near the free surface have been implemented. The VOF technique is validated against the classic dam-break problem, as well as series of 2-D sloshing experiments and results from SPH calculations. These and a series of other examples demonstrate that the present CFD method is capable of simulating violent free surface fows with strong nonlinear behaviour.