The Influence Of Spray Rails And Stern Flat On Planing Hull Resistance Performance

Due to the preponderance of planning hull in its low construction cost, simple structure,high reliability and excellent fast performance, it has been widely applied .The combination of the spray rails and stern flat, which is considered as an effective scheme reducing the resistance of the planning hull, is widely used in various types of planning craft.In previous work, the impact of spray rails and stern flat appended to the planning hull were mainly implementing through the model test. A further study, in this paper, the method of CFD has been approached to the simulation of the calm water towing test of planning hull.Comparing with the experimental values, it shows that the CFD method simulate the process well. In addition, with the simulation, it can predict the reducing drag mechanism of the spray rails and stern flat well.In this paper, effects of the elements, on the resistance performance of the planning hull,with which the spray rails installed, such as position, amount of spray rails, length, and the mounting angle have been discussed. A series of models with different parameters have been set up for a compare. With an analysis of resistance value, wetted area and pressure distribution contours and heave trim value etc., the effects of different parameters on spray rails’ resistance reduction performance have been discussed. In the meantime, an analysis of the frictional resistance and residual resistance variation, between if the spray rails were installed, shows the reducing drag mechanism of the spray rails.Calculation and analysis results show that the distance between the spray rails and the middle of the hull have an effect on the drag reduction, the closer the better. With the increase of installed amount, the drag reduction effect of spray rails increases; however, the length of spray rails has few effects on the drag reduction. In this paper, among three couples of spray rails, all that is needed is adjusting the mounting angle of the outermost pair of spray rails to a certain value to get an excellent resistance reduction situation. And the certain angle value always 30 degrees. On the other hand, the results show that the influence of spray rails mainly act on the frictional resistance, and little on residual resistance.Stern flat is mainly used for navigation attitude adjustment. And the parameters of stern flat considered in this paper are length, mounting angle and the installation location. With the similar analysis method above, results show that the length of the stern flat has little influence on the drag reduction, and In order to keep a good drag reduction and navigation attitude under different speeds, the mounting angle of stern flat is different, which is depending on the speed etc. What’s more,the Installation position of a stern flat,about 0.3B away from the longitudinal section in center plane can make the bottom of the planning hull pressure becomes well-distributed, and a lower hull trim and heave value, decrease the residual resistance , meanwhile the friction resistance do not increase.