ECONOMICAL CARGO SHIPS—SOME MODEL EXPERIMENTS. 49 
lines on Fig. 8, and the resistance of the twin-screw bossing for this model is also 
given as indicating the augmentation of resistance which is produced on twin- 
screw ships. 
In order to fully utilize these results in the design of a cargo ship, Fig. 21, 
Plate 24, was prepared. This diagram is laid off on prismatic coefficients, both for 
fore body and after body, which are independent of one another, and when the 
necessary prismatic coefficient of each end is chosen from one of the figures (15 to 
20), it is immediately possible to lay off a curve of areas for the prismatic coeffi- 
cient of each end from Fig. 21. The amount of parallel middle body is also shown 
so that the entrance and run may be divided up equally and the sections made to 
correspond to Fig. 8. As it is necessary, usually, in designing a ship, to have pretty 
accurate knowledge of the height of transverse metacenter at an early stage of the 
work, a new diagram, Fig. 22, Plate 25, has been devised by the writer. It gives 
the location of the transverse metacenter from the load waterline as a coefficient 
of the beam of the ship at various draught ratios and at three prismatic coeffi- 
cients, but it is noteworthy that the prismatic coefficient has an extremely small 
influence on the stability at draught ratios such as are adopted in ordinary mer- 
chant ships. For example, a ship of, say, 50-foot beam at a draught of 19 feet 
6 inches shows no change in metacentric height between the prismatic coefficients 
of 0.68 and 0.84, the metacenter being about 16% inches above the load waterline 
in each case. This diagram is strictly true, of course, only for ships of form given 
in Figs. 8 and 21, but it will be found that it gives reasonably accurate results for 
any ship within the range of coefficients covered. 
