SeN 
OF FORM OF SHIPS UPON THEIR RESISTANCE. 61 
the average coefficient of bow and stern or the coefficient for the whole water- 
line. It is seen that the variation of wetted surface is not great. It is, 
in fact, materially less for practical cases than might be supposed from the 
first glance at Figs. 9 and 10, Plate 7. This for the reason that Figs. 9 
and 10, Plate 7, extend to coefficients of water-line plane, etc., beyond 
those that would be adapted in practice. 
Thus, considering Fig. 9, Plate 7, we would not expect to find in practice 
a vessel whose water-line coefficient was less than its longitudinal coefficient 
so that the larger wetted surface coefficients in Fig. 9, Plate 7, to the left 
of the water-line coefficient 0.6 are beyond practicable regions. 
Bearing this inmind we may safely say from Figs. 9 and ro, Plate 7, 
that the effect of practicable variations of shape of sectional area curves 
and water-line fineness upon wetted surface are comparatively small. Fine 
ended curves of sectional area result in somewhat greater wetted surface, 
but the difference indicated in Figs. 9 and 10, Plate 7, is not more than 
2 per cent. or so for the very great variations of sectional area indicated in 
Figs. 2 and 3, Plates 3 and 4. 
Let us take up now the experimental results. Fig. 11, Plate 8, shows 
typical curves of total resistance for the three models from Series No. 29, 
whose body plans are given in Figs. 3, 4 and 5, Plates 4 and 5, and the 
three models from Series No. 32, whose body plans are given in Figs. 6, 7 
and 8, Plates 5 and 6. 
Bearing in mind that comparatively few vessels are driven at speeds 
greatly above that corresponding to 4 knots for the 20-foot model, it is seen 
from Fig. 11, Plate 8, that the variation of resistance corresponding to very 
radical variations of form of the three models in each case are after all not 
great. 
It is interesting to note the critical speed, a little above 4 knots, at 
which the models change place materially. Models Nos. 1092 and 11091, 
which are of the extreme type, combining full ended sectional areas and fine 
ended water-lines are the worst below 4 knots, while between 4 and 5 knots 
they show themselves the best. © This is a typical result and shows that the 
features of a model should be adapted to suit the speed. 
Taking up now the question of residuary resistance rather than the 
total resistance, Figs. 12, 13, 14 and 15, Plate 9, show the residuary 
resistance in pounds per ton plotted on speed length ratio for a number 
of models of Series No. 29, grouped by curves of sectional area. 
Figs. 16, 17, 18 and 19, Plate 10, show the same curves grouped by 
water-lines. Figs. 20 to 27, Plates 11 and 12, give similar information for 
Series No. 32. It will be observed that considering Figs. 12 to 15, Plate 9, 
