Bowthruster-induced damage

Abstract

The stability of stones in propeller-induced jet wash is still difficult to predict. Especially the trend of bowthrusters increasing in size and power in sea going ships (especially ferries) over the last years may be a reason for concern when dealing with the protection of slopes and beds. But also ships used in inland navigation are using bowthrusters more intensively. Because of high costs of crew, many inland navigation ships try to sail with a minimum of crew. In order to allow mooring with a limited number of staff, the manoeuvrability of the ship has to be improved, which is often done by making a bowthruster in the ship. At this moment near mooring dolphins in the navigable rivers of the Netherlands managers are confronted with damage to the slope protection because of heavy use of bowthrusters. From these the conclusion can be drawn that it is necessary to improve design formulas for the effect of a bowthruster, as also suggested by Römisch and Hering (2002). The second step is then to make a conceptual model of the effect of (propeller-induced) turbulence on the stability of the slope, followed by a systematic set of tests in the lab in order to verify the conceptual model and in order to determine the calibration constants in the conceptual model.