THE PROBLEM OF THE HULL AND ITS SCREW PROPELLER. 173 
Correction for Variations in H + B. 
The ratios H + B for type 3 ships, corresponding to the nominal B. C.’s as 
given by line 4—B, are given by the curves on Figs. 1 and ta, Plates 71 and 72, 
marked H + B, type 3, standard, while those for types 1 and 2 vessels are given 
by the curves on the same figures marked H + B, type 2, standard. There will be 
noted diagonal curved lines extending from above at the left to below at the right 
of the figures, marked with the values of the nominal B. C.’s as taken from line 
A—B for type 3, and from C—D for types I and 2. These are direction lines to - 
follow in correcting for values of H + B less than standard, on Fig. 1, and for 
greater than standard on Fig. fa. 
Example illustrating the above method of estimating the S. B. C. of a vessel. 
To illustrate the above, two vessels will be taken :— 
VessehAre iNormalib) Cin — 632 
IB me IL Wy ify Wa) Say 0G 
H+=B = .3 
2 LAN B= Ay 14.66 
Examination of the after-body lines discloses that these lines fine rapidly due 
to a rapid falling away in beam and are convex. This indicates that the hull is of 
type 3 form. 
The coefficient of midship section = .930. 
Vessel B: Nominal B. C. Sol AA 
Je Po IU) RN IE eae arte 
Jel 2 J; = .5 
BM, Vale 185/42 JEL) igs 
Coefficient of midship section = .98 
Examination of the after-body lines discloses that these lines fine rapidly due toa 
rapid decrease in draught of the actual full body of the hull, the beam being de- 
creased very slowly as the stern is approached, while the screw is completely 
covered by the hull, in the case of twin screws. These conditions, in conjunction 
with any value of H+B, indicate a hull of type 2. 
Vessel A, Type 3. 
Plotting vessel A on Fig. 1 with a nominal B. C. of .632 and a value of 
B+L. L. W. L.=.16, and drawing a line through this plotted point and the point 
on the base line where B. C.=1.0, this line is found to cross the line A—B at 
B. C.=.535. Erecting an ordinate from this point on A—B to the value of 
H~B=.3 below the curve H+B, type 3, standard, and following the direction 
lines up to this curve, the corrected B. C. on A—B is found to be .505. Through 
this point .505 on A—B draw another line through the base at 1.0. Where this 
