Hydrodynamic study of a double-stepped planing craft through numerical simulations

Abstract

This paper investigates the performance and hydrodynamic characteristics of a double-stepped planing hull and the effects of adding two steps to the bottom of a mono-hull. To study these effects, a non-stepped model with similar characteristics of a stepped hull is also modeled. The numerical simulations are conducted in different stages. First, a mesh study is performed and an optimum mesh size is adopted. Subsequently, the predicted resistances are compared against experimental data and good agreement is observed. Later, the targeted simulations are performed at five different Froude numbers and various characteristics are determined. The results of these studies indicate that frictional resistance of the double-stepped model is drastically smaller than that of the non-stepped model, while pressure drag of the stepped vessel is slightly larger than the non-stepped model. It is observed that adding steps to the hull does not reduce the wetted surface at lower Froude numbers, but its positive effect appears when Froude number exceeds 2.0. It is also seen that generated transom wave behind the double-stepped hull is larger than that of the non-stepped hull. In addition, the computed pressure distributions over the center line of both models indicate that the first maximum pressure of the double-stepped model is larger than that of the non-stepped hull. Ultimately, it is concluded that hydrostatic pressure has an essential role in producing the lift force of a non-stepped planing hull, but this pressure has very little contribution in generation of the lift force of the double-stepped hull.