ONR Hydrofoil Boat XCH-6 229 
that the cavitation-free speed at the surface may be increased from 20 to over 50 percent by 
use of the parabolic cross section. The lift-to-drag ratio, however, is decreased. 
MCA /6-SERES —e — CAMBERED PARABOLA 
PARAMETERS RESULTS ASSUMPTIONS - 
Ze [eo Ya) | Scarmmae | BLN? HOW 
Cawer) © Fe*2X10", "0039 
3. EQUAL C, AMD Ye 
4 CURCULARARC CAMBERLME 
SK <<¢L0 
18-SERIES. 
PARABOLA 
46 -SERVES. 
PARABUA 
-O10/ -67 
i166 $0) 
-WOf 25 )\.5/ 
15- SERIES 2099 53.55 
PARABOLA OU? 43 6 &=0° 
16- SERIES 7 R=08 
PARABUA 
4E-SERIES, 
PARABOUA 
16-SCRIES 
PARABOLA 
O08 27 '|-39 
one 2 
0086 58 
0088 $7 
25 
ee 29 a 
Fig. D11. Comparison of hydrofoils having equal lift coefficients and thickness-to-chord ratios 
6 WOSWELPLACK 
Figure D12 shows a vented hydrofoil which is designed for optimum efficiency. It is 
constructed by first designing a strut having a thickness distribution and cutoff trailing edge 
which provides zero cavity drag in accordance with Tulin’s linearized cavity theory for zero 
cavitation number. This strut is then cambered in such a manner that the pressure on the 
ASSUMPTIONS: N=0, 02=0° CIRCUIAR ARC CAMBER LINE, AR = 08, 
a ee TURBULENT FLOW, Ge = 00089 
CUT-OFF FOR 
fill: iano 
t=O \— CUP OUT TOREDUCE 
FRICTIONAL DRAG 
QOs3 
Fig. D12. Base-vented hydrofoil having optimum efficiency 
