48 ECONOMICAL CARGO SHIPS—SOME MODEL EXPERIMENTS. 
original curve of areas A, but of the same prismatic coefficient as BX and CX. 
Special attention must be drawn to the development of the hump in these three 
models, all of identical prismatic coefficients, and the emphatic increase in re- 
sistance which AX shows compared with BX and CX at a speed corresponding to 
10 knots for a 400-foot ship cannot be lost sight of, because this illustrates a danger 
to which naval architects are exposed in departing from known models from which 
resistances are estimated. 
SERIES 1130. 
Series 1130 represents a model of a single-screw cargo ship as shown on Fig. 
8, Plate 22, which gives cross-sections of the entrance and run, the parallel body 
being omitted. This model has a very small cruiser stern which, at the draught 
reported herewith, was only sufficient to carry the lines and curve of areas to 
the aft perpendicular. Generally the aperture in a single-screw steamer makes 
the displacement length 2 per cent or 3 per cent less than the length between 
perpendiculars. In this series the various combinations of entrance and run 
produced in all 18 models for the single-screw type, and there was a twin-screw 
model of ‘‘DW”’ modified, both with and without bossing. The twin-screw 
model was tested at Washington only, and the “DW” was tested both at 
Washington and Ann Arbor. All these models were tested at draught ratios of 
0.489, 0.435, 0.351, 0.261, with the exception of the twin-screw model, where the 
displacements were held identical and the draught ratio was therefore very slightly 
reduced; but in order to keep this paper within reasonable compass the results 
at 5=0.435 only are presented herewith. 
Fig. 9, Plate 23, indicates the angles of entrance and run corresponding to 
these models, and standard curves of areas of the two extremes of the W series 
are shown. These standard curves of areas are plotted in such a way that the 
actual area of curve in each case is identical, thus indicating in what part of the 
ship the displacement is carried. For this purpose, the midship area is laid out 
equal to 100 divided by three times the prismatic coefficient. In Figs. 10, 11, 
12 and 13, Plate 23, these resistance curves are presented where each after body 
is shown with three or four different fore bodies, one or two curves having been 
left out of some of the diagrams to prevent confusion. Resistance curves could 
equally well be assembled with identical fore body and varying after body, and the 
student will find advantage in laying them out this way. 
In Figs. 15 to 20, Plate 23, the curves of resistance shown in Figs. 8 to 
II are assembled in accordance with the prismatic coefficient, and these curves 
will probably prove of more use to anyone desiring to utilize this series of experi- 
ments for design purposes. Cross curves of each of these diagrams can also be 
plotted similar to those shown in Figs. 4 and 5 and, if this is done, it becomes a 
simple matter to select the best ¢«/p ratio for any particular speed. 
Fig. 14, Plate 23, shows the comparison between single-screw vessels and a 
ship of similar lines to DW with the aperture filled in as indicated by the dotted 
