عباس دشتی منش

Change in body shape characteristics, is one of the ways to reduce the resistance and thereby increasing speed of the 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 to small parts with higher width-length ratio in high velocities and in this situation, the generated lift force is more efficient. In this paper, 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 show that the numerical solution for resistance, trim and lift are relatively precise in comparison with model test data. Furthermore, various hull characteristics such as wetted length of keel, chine wetted length, spray angle and ventilation length have been investigated.