16 



TRIM, T, DEG 



Figure 7. Effects of deadrise, l m /b = 3.0. 



Dead rise. — The results for various angles of dead rise are compared in Figure 

 7. With sharp-edged models, the three coefficients established for the flat plate appear 

 to remain constant for angles of dead rise up to 50°. Variations with dead-rise angle 

 are uniform through the trim range and exhibit the usual nonlinear characteristic 

 associated with theoretical dead-rise functions. 



Cross section. — Practical hulls and hydro-skis with dead rise usually require 

 some form of chine flare to control spray, and many model tests have indicated 

 additional benefits from the use of flare on resistance and stability. This experience is 

 substantiated in Figure 8, which shows the progressive increace in lift coefficient 

 obtained with horizontal flare and vertical strips on a rectangular-plan-form surface 

 with a basic angle of dead rise of 20°. The experimental data correlate with the 

 theory entirely on the basis of an increase in the crossflow-drag coefficient as noted. 

 The center-of-pressure coefficients remain constant as before, hence the center-of- 

 pressure ratio is reduced only slightly by the chine modifications. 



The corresponding effects for a basic dead rise of 40° are shown in Figure 9. 

 The same trends are obtained to an even greater degree with larger apparent values 

 of the cross-flow-drag coefficient and the same constant center-of-pressure coefficients. 

 These results indicate that the Shuford formulation provides a means of obtaining the 

 planing characteristics of an arbitrary cross section over a wide range of operating 

 parameters with only a brief experiment to determine the constant value of the cross- 

 flow-drag coefficient. 



Triangular plan form. — The application of the theory to a flat surface with a 

 pointed plan form such as preferred for hydro-ski trailing edges is shown in Figure 

 10. Good correlation with unpublished experimental data is obtained with the same 

 sharp-chine crossflow-drag coefficient as for rectangular plan forms. In this case, 

 however, the lifting-line component of lift apparently effectively acts at the leading edge, 



192 



