Performance Prediction of Two-Stepped Planing Hulls Using Morphing Mesh Approach

Abstract

Change in body shape characteristics is one of the ways to reduce the resistance and thereby increasing the speed of planing hulls. Creating the transverse steps is one of these variations. The main reason to use the steps in high-speed planing craft is that the wetted surface of the vessel is divided into small parts with higher width-length ratio in high velocities and in this situation, the generated lift force is more efficient. In this article, by performing a three-dimensional numerical solution, motion characteristics of a two-stepped planing hull with transverse steps in calm water have been examined. For this purpose, the vessel is free to trim and sinkage, and by using the morphing mesh approach, the numerical simulation continued until the equilibrium condition of the two-stepped planing hull is satisfied. Resistance, lift, trim angle, and wetted surface in various velocities have been computed and compared against existing experimental data. Analysis of considered two-stepped hull in calm water shows that the numerical solution for resistance, trim, and lift are relatively precise in comparison to model test data. Furthermore, various hull characteristics such as wetted length of keel, chine wetted length, spray angle and, ventilation length have been investigated. 1. Introduction In recent years, naval architectures have proposed significant modifications in planing hulls' design by creating steps, tunnel, and other geometric features. By considering these geometric variations, the hull wetted surface and, consequently, its resistance have been reduced and planing hulls velocity can be increased. In this regard, the step is one of the main hull's modifications which can lead to resistance reduction. Generally, lift of stepped planing hulls is distributed over the forward, middle, and stern plane of the hull (Fig. 1), and therefore, its ride quality will also be improved. Moreover, planing hulls with various step configurations have been used in high-speed craft since 1910, and various types of step with different shapes and arrangements have been used in planing hulls.