A new series of physical model tests were conducted to analyse the behaviour of a breakwater core when it becomes exposed to wave attack. The emphasis of this research was on the measured influence of a wide stone grading on both the deformation of a breakwater trunk and the occurring longshore transport. This behaviour was investigated for both head-on and oblique waves using two different wave loads. The findings were compared to the currently available formulas and the validity of these formulas for the tested range of parameters was (re)checked. In general a clear distinction was found in the processes between tests with narrow grading and wide grading. It turned out that both the parameters describing the two-dimensional deformation and the longshore transport show an increase for wider grading.