High-Speed Planing Hull for Rough Water 



configuration. 



In designing a double chine configuration, it is important 

 that the upper chine location be within the cavity found by the boundary 

 of the flow separation from the lower chine. As shown by Korvin- 

 Kroukovsky (Reference 9 ), the trajectory of the free streamline re- 

 presenting the cavity of the boundary is a function of deadrise angle. 

 Figure 1 1 of the present report, which is taken from Reference 9, 

 plots the separation trajectory for various deadrise angles. It is seen 

 that the width of the separation cavity increases with decreasing dead- 

 rise angle. If the upper chine is located outboard of this cavity bound- 

 ary, the originally separated flow from the lower chine will reattach 

 to the bottom somewhere between both chines and thus preclude com- 

 plete flow separation from the lower chine. In the present design, the 

 outer deadrise angle is 45° and the outer chine is approximately 

 0. 80 ft. outboard of the inner chine. This is sufficient to clear the 

 lower chine trajectory at station 5 and result in complete separation 

 from the lower chine. Observations of the wetted bottom areas during 

 model tests confirmed this prediction. 



Section Shapes 



The section shapes are slightly convex. This section pounds 

 less than others of equal deadrise because there is less likelihood of 

 instantaneous water contact over large bottom areas. 



Planform Shape 



At high planing speeds, when dynamic lift predominates, it is 

 usual to narrow the beam towards the stern. This reduces bottom 

 friction without a noticeable loss in lift. The narrow transom also 

 avoids the possibility of reattachment of the separation cavity formed 

 in the region of maximum beam. For the present design, the transom 

 width was determined by considerations of space requirements for 

 the auxiliary machinery in the stern area. This resulted in a slight 

 reduction of beam towards the stern which, in the model tests, was 

 found to be sufficient to avoid flow reattachment. 



Bottom Warp 



The increase in deadrise with length forward of the transom 

 is referred to as bottom warp and is required to provide a relatively 

 high deadrise in the bow regions. Brown (Reference 10) has shown 

 that there is a slight reduction in planing efficiency for moderate va- 

 lues of warp. The slightly convex bottom sections, from keel to lower 

 chine, used in the planing area aft of the high-speed stagnation line 



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