The Xbloc armour unit derives its hydraulic stability from its self-weight and by interlocking with surrounding units. Due to the highly porous armour layer (layer porosity of almost 60%) constructed with Xbloc units, the energy of the incoming waves will be largely absorbed. The Xbloc armour layer is therefore able to protect the rock in the under layer from erosion due to waves. Besides empirical formulae derived from physical model testing, the interaction between breakwater elements (submerged or emerged) and waves as well as the filtration of the fluid into the porous breakwater has been investigated amongst others by MEDUS, based on RANS equations coupled with a RNG turbulence model.