A method to improve the prediction of ship resistance in shallow water

Abstract

The traditional approach of extrapolating the experimentally measured model resistance of a ship to full scale is based on the Froude assumption or the form factor assumption, where the viscous part and wave-making part of the resistance are dealt with in deep water. In shallow water, however, the water-depth dependency of flat-plate/ship frictional resistance as well as form- and wave effects are expected. It is found in this research that all of these three properties are deviating more or less clearly from the traditional understanding from certain water depths. In this dissertation, a correct understanding of the resistance of ships in shallow water from the very basis is provided to build a new approach to improve resistance prediction considering the water-depth dependency of the three features mentioned above. A method is proposed to improve the extrapolation of ship resistance for model-scale tests carried out in shallow water. The effects of limited water depths on the three components of ship resistance (i.e., frictional resistance, viscous pressure resistance, and wave-making resistance) have been studied individually. Empirical formulas have been developed for three ship types in various water depths. This approach can benefit all further qualities of the ship, e.g., a reliable performance prediction, truly valid rules for ship design and even future work on understanding ship propulsion in (extremely) shallow water when navigating in inland waterways and coastal waters. It also allows the further application of the well-accepted extrapolation method with at the same time taking into account the inherent deviations in shallow water.