62 SOME MODEL BASIN INVESTIGATIONS OF THE INFLUENCE 
for instance, two of the curves in each case refer to the straight series 
and two to models obtained by interchanging bows and sterns. ‘There is 
in each figure a curve for a model having the finest ended water-line and 
one for the model having the fullest ended water-line. There is then one 
curve where the finest ended water-line forward is used with the fullest 
ended water-line aft and finally a curve where the fullest ended water-line 
forward is used with the finest ended water-line aft. In Figs. 12 to15, Plate 
9, the sectional area curve for each figure is the same. Similarly, in Figs. 
16 to 19, Plate 10, each figure refers to a common water-line, the sectional 
areas differing. Figs. 20 to 27, Plates 11 and 12, give much the same 
information as regards Series No. 32 as Figs. 12 to 19, Plates 9 and 10, for 
Series No. 29, being similarly grouped. 
A study of all these figures will show the tendency to straighten out or 
change relative positions beginning roughly at or a little below the speed 
length ratio of 0.9, corresponding closely to a 4-knot speed for a 20-foot model. 
Considering Figs. 12 to15, Plate 9, in every case the fine bow appears 
to be the best at low speeds. Moreover, the fine bow in combination with 
the full stern appears better than the fine bow in combination with the fine 
stern. At higher speeds the fine bow with the full stern loses its superiority. 
Considering Figs. 20 to 23, Plate 11, while the fine bow appears to be 
a little the best at low speeds, it does not show as much superiority as it 
does for the Series No. 29, and at the higher speeds too the fine bow is 
relatively worse. 
Considering Figs. 16 to 19 and 24 to 27, Plates 10 and 12, we see that, 
broadly speaking, the fine ended curves of sectional area have the better of 
it at and below a speed length ratio of about 0.9, while at the high speeds 
they are the worst in every case. 
It was diffcult to separate the effect of the bowfromthestern. Undoubt- 
edly the resistance of a given stern will be different as it is combined with 
varying bows, and vice versa. 
Itwasnot practicable to test all bows with all sterns, as this would involve 
testing 256 models for each series. Some investigation was made, however, 
of the stern effect by combining a single bow with all 16 sterns in each case. 
The common bow used was that of Model No. 1201 where No. 3 water- 
line—a rather full line—was combined with Sectional Area Curve b, a rather 
fine ended type. The curves of residuary resistance deduced from trials 
with the 16 sterns are shown in Figs. 28 to 31, Plate 13. 
Thus grouped by water-lines they show remarkably small variation for 
all speeds, indicating that we may materially vary shape of curves of sec- 
tional area aft without material effect upon resistance. 
