THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 177 
pitch and to the desired blade sections, which were the same type for all the pro- 
pellers and highly polished. 
The trials were run by competent and experienced men, while the data were 
taken and computed by trained observers and engineers. There was every rea- 
son to believe that what were collected were as reliable as could ever be obtained 
under actual ship conditions. 
Derivation of Design Curves. 
Taking the derived data and from it obtaining values of pounds indicated 
thrust per square inch of disc area (I. T.p) of the propeller, and corresponding 
pounds propulsive thrust per square inch of projected area (P. T.,), a series of 
curves were plotted with I. T.p as abscissas and P. T., as ordinates, and inter- 
mediate curves for intermediate projected area ratios were interpolated. 
Curves of corresponding tip speeds in feet per minute (T. S.), and of propul- 
sive coefficient (P. C.) were also laid down, as were also the curves of apparent 
slip (S). 
At one point on each of the established curves of I. T.p>—P. T., a decided 
change in conditions was found to occur, the curve either taking a sudden rapid 
rise or beginning to fall rapidly. 
The values of these points in I. T.p, T. S., P. C., and S were taken and plotted 
on values of P. A.D. A. (projected area ratio), as abscissas and the equations to 
the curves obtained when possible, that for I. T.p being— 
On P. =) 
I. T.p=28.41 i 
while that for T. S. is— 
PLA 
T. S.=38148 i= =) 8365-2 (BA 
Equations to the curves of P. C. and of S could not be obtained. ; 
These curves are shown on Fig. 4, Plate 75; the conditions covered by them are 
denoted “Basic Conditions”’ and are constant with the exception of the S curve 
which, it will be noted, is based on S. B. C. as abscissas and not on P. A.+D. A. 
In other words, each standard S. B. C. has its constant standard basic slip. 
This curve of S is again shown on Fig. 5, Plate 76, but is there based on 
values of 2 X length of after body of the ship + the draught, which brings in the 
final correction for hull form already mentioned. 
Correction of S for Varying Values of 2L. A. B. + H. 
On Fig. 5 is shown a curve marked ‘‘Slips for S. B. C. on X—W, Type 1 and 3 
Hulls.” This curve is in reality the same as the curve of S shown on Fig. 4, but in 
the case of Fig. 5, it is erected on abscissa values of 2L. A. B. + H instead of on 
S. B. C., and the S. B. C. values are marked on it at the standard values of 
2L. A. B. + H as determined from Fig. 1. 
