As a ship approaches shallow water, a number of changes arise owing to the hydrodynamic interaction between the bottom of the ship’s hull and the sea floor. The flow velocity between the bottom of the hull and the sea floor increases, which leads to an increase in sinkage, trim and resistance. As the ship travels forward, squat of the ship may occur, stemming from this increase in sinkage and trim.

Knowledge of a ship’s squat is necessary when navigating vessels through shallow water regions, such as rivers, channels and harbours. Accurate prediction of a ship’s squat is therefore essential, to minimise the risk of grounding for ships. Similarly, predicting a ship’s resistance in shallow water is equally important, to be able to calculate its power requirements.

There have been various approaches to predict squat and shallow water resistance. These methods comprise empirical or analytical investigations and experiments. The analytical methods mainly use the assumptions from potential flow theory, presuming the ship to be a slender body. The empirical formulae also have certain constraints and conditions to be satisfied. In addition, conducting towing tank experiments may be costly and time consuming. On the other hand, CFD techniques are easily capable of predicting the trim, sinkage and resistance of a vessel in shallow water, incorporating both viscous and nonlinear effects in the flow and free surface.

The key objective of this study was to perform fully nonlinear unsteady RANS simulations to predict the squat and resistance of a model scale Duisburg Test Case advancing in a canal. The analyses have been carried out in different ratios of water depth to ship draught at various speeds, utilising a commercial CFD software package. The squat and resistance results obtained by CFD have then been compared with available experimental and numerical data.