46 ECONOMICAL CARGO SHIPS—SOME MODEL EXPERIMENTS. 
presented to this Society a couple of years ago, are shown on Fig. 1, Plate 15, and 
Fig. 2, Plate 16, gives Taylor’s standard series plotted as C curves for 400 feet 
427.1 
‘ Ai 
designated X by means of which the effective horse-power may be immediately 
arrived at from one diagram. Areas of the various sections at different prismatic 
coefficients for Taylor’s series are shown on Fig. 3, Plate 17, in order that the form 
of Taylor’s models may more readily be compared with the series here presented. 
In addition a diagram, Fig. 4, Plate 18, is presented, showing the theoretical 
difference between tank tests as extended by the various coefficients of friction 
now in use at Ann Arbor, Washington, and in England. ‘These curves are based on 
the assumption that the actual friction of a model of unit length at the three tanks 
is identical, but careful comparisons between tests of the same model made at 
Ann Arbor and at Washington seem to indicate that the Washington resistances, 
particularly for models of high displacement, run somewhat higher than can be 
anticipated from these curves. Whether this is due to some interference in the 
stream lines, due to the cross-section of the Washington model being larger in 
proportion to the section of the tank than is the case at Ann Arbor, or whether it 
is due to elements of eddy making not yet properly understood, or simply to the 
actual difference in the surface of the models, is yet unknown to the writer. 
Because of the uncertainty of what is the true frictional resistance of these 
models, the method adopted at Ann Arbor of using Tideman’s coefficients has been 
accepted for use by the writer in extending present results, and we thus secure very 
conservative resistances. 
That the Ann Arbor estimates of effective horse-power for slow-speed cargo 
steamers appear to be very close to the actual effective horse-power required for 
the ship has been demonstrated in quite a large number of cases, and I think this 
might be explained by Baker’s theory of the augmentation of frictional resistance 
in‘full'ships, due to the nature of the wave profile and the resultant acceleration of 
velocity of the water at the surface of the vessel, and the magnitude of this in- 
crease in resistance is roughly equal to the difference between effective horse- 
powers calculated by Froude’s method and effective horse-powers calculated by 
the Tideman formule. I have not been able to ascertain whether Baker has 
applied this correction to his model resistances as recommended in his book* before 
compiling his C constants given in his recent papers. 
All results given herewith have been standardized for a water temperature 
Ot 70) 10% 
Those who have prepared the lines of vessels with parallel body will recognize 
that it is difficult to state definitely the point where entrance and parallel body 
combine, and that this point may be varied very considerably with an extremely 
small variation in the form of the ship. For this reason it was found necessary, in 
order to make comparisons fair, that an analysis length of entrance and run should 
be devised. At the same time it has been demonstrated repeatedly that the form 
length, together with C correction curves for other lengths, and a curve of 
*“Ship Form, Resistance, and Screw Propulsion,” paragraph 10. 
