Ship-induced local scours by propeller jets cause considerable damage around harbour structures. This study investigated the local scour around piles and pile groups. In the case of pile clusters, group effects become important, as does the angle of orientation of the pile groups to the prevailing direction of waves and currents. The main factors to consider are flow interference leading to enhanced flow speeds or turbulence at adjacent piles in some cases and sheltering of piles in others. The propeller jet was simplified using a circular water jet on the cohesionless sediment bottom in this study. The study showed that the maximum equilibrium scour depth around a pile was primarily a function of the densimetric Fronde number. The scouring around the pile groups was also found to be dependent on densimetric Fronde number (Fr-d), the distance between the piles to pile diameter defined as clearance ratio (a/D) and the relative size of the pile to circular water jet diameter (D/d(o)). (C) 2004 Published by Elsevier Ltd.