130 M. P. Tulin 
where Cy, is the foil lift curve slope, Cz is the equilibrium lift coefficient, Up is the 
speed of advance, and v is the seaway-induced vertical velocity. If rms g loadings are 
desired, then rms values of V are to be used in computation. The quantity 
Cr /CLU0 
at design speed is a characteristic of the craft, while the quantity V depends on the envi- 
ronment. Clearly, if minimum dynamic loadings are desired, then the parameter 
CL, /CLY 
should be minimized in design. 
In Fig. 7 are shown calculated values of this parameter as a function of speed, for a 
family of subcavitating and supercavitating hydrofoil wings. The former was selected with 
wing lift coefficients, thickness ratios, and aspect ratios varying from 0.35, 0.11, and 7 
(respectively) at 45 knots to 0.15, 0.05, and 3.3 (respectively) at 70 knots and in such a 
way as to maintain approximately constant wing stress and satisfy cavitation inception con- 
siderations at each speed. The operating depth of submergence is for all wings taken as 
one mean foil chord. The supercavitating wings were taken in two versions, utilizing in 
one case thin low-drag foil sections (t/c =~ 0.08) with aspect ratios and lift coefficients 
ranging from 5 and 0.18 respectively at 60 knots to 3.4 and 0.16 respectively at 90 knots, 
and in the other case thicker foil sections (t/c =~ 0.16) with aspect ratios and lift coeffi- 
cients ranging from 8.1 and 0.26 at 60 knots to 5.6 and 0.23 at the higher speed. All of the 
supercavitating wings considered are designed for approximately equal maximum nominal 
stress and are optimized with respect to lift-drag ratios. 
The dynamic loads parameter is seen to be generally larger for subcavitating wings, 
mainly as a result of the higher sectional lift curve slopes of subcavitating foils relative to 
supercavitating sections. It will be recalled that at infinite depth, the former are about 
Current Prop Transport (300 knots) 
Current Jet Transport (530knots) 
Projected Jet Transport (2000 knots) 
Dynamic Loads Parameter, C, . /C. Up, in sec /ft 
60 
Hydrofoil Craft Speed, Uy , in knots 
Fig. 7. Dynamic loads parameter Cz, /C,Uo for a family of hydrofoil craft 
