When a large ship enters a port the vessel is navigated by the pilots instead of the captain due to safety reasons. The final part of the berthing manoeuver is the most critical and consists of the vessel moving laterally towards the quay wall. At this point the vessel does not use its own propulsion force anymore but is pushed by the tugboats. During this lateral berthing manoeuver a resistance force can be noticed counteracting the lateral manoeuver to the quay which acts as hydraulic damping. A large force is needed to overcome this hydraulic damping which is known as the water cushion effect. There are a handful of circumstances that are suspected to enhance the effect of hydraulic damping, but a substantiated conclusion is not yet drawn. To determine the mechanisms causing the hydraulic damping during ship berthing, field experiments in the Port of Rotterdam are carried out and analysed. In addition, a one-dimensional theoretical model is developed to simulate the field experiments and investigate the flow behaviour around a berthing ship.