An Experimental Study of Hydrodynamic Performance of a Planing Hull Due to the Improvement of Stern Flap: The Effects of Form and Angle

Abstract

The stern flap and stepped hull are widely applied for high speed vessels to reduce resistance by adjusting the performance attitude. In this present study, a form design of stern flap has been improved on the high speed ferry as a planing hull, namely I and 2V. The stern flap was attached on the transom stern of the planing hull installed at several angles of 10, 20, 30 degrees. The free running model test and resistance analysis of the planing hull were carried out to determine the effects of the improved stern flaps on the parameters of trim by stern, resistance, and speed. The planing attitude of planing hull captured in the model test were analyzed using the application of Maxsurf Resistance. The study results revealed that both the stern flaps I and 2V on the planing hull afford to reduce the trim by stern, resistance, and to improve speed. The average value of the difference of the increase of trim by stern between the stern flap 2V and stern flap I is 1.79%. With the constant FnV, the planing’s resistance can be reduced by the increase of the stern flap angles. The average value of the reduction of planing’s resistance due to the increase of the stern flap angles is 6.27% for the stern flap I, and 5.05% for the stern flap 2V. Regarding the effect of the stern flap form with its angle on the planing’s resistance, the planing’s resistance due to the stern flap 2V is lower compared with the stern flap I wherein overall the average difference is 4.73%. The reductions of the trim by stern and planing’s resistance due to the stern flap form and angle are caused by the vertical lift force and pressure distribution acting on the transom of the aft planing hull.