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XVIII. On the Delation of Form and Dimensions to Weight of Material in the Construction 
of Iron-clad Ships. By E. J. Reed, Chief Constructor of the Navy. Communicated 
hy Professor G. G. Stokes, Sec. B.S. 
Received March 3, — Read March 19, 1868. 
The object of the present paper is to show that the proportion of length to breadth in 
a ship, and the form of her water-lines, should be made in a very great degree dependent 
upon the weight of the material of which her hull is to be constructed — that an armour- 
plated ship, for example, should be made of very different proportions and form from 
those of a ship without armour, and that as the extent and thickness of the armour to 
be carried by a ship are increased the proportion of length to breadth should be dimi- 
nished, and the water-lines increased in fulness. 
It is highly desirable that this subject should receive the attention of men of science, 
not only because it bears most directly upon both the cost and the efficiency of future 
iron-clad fleets, but also because it opens up a theoretical question which has hitherto, 
I believe, received absolutely no consideration from scientific writers upon the forms and 
resistances of ships, viz. the manner in which the weight of the material composing the 
hull should influence the form. 
Prior to the design of the ‘ Bellerophon,’ the forms of ships were determined in com- 
plete disregard of this consideration ; and even the most recent works upon the subject 
incite the naval architect to aim always at approaching the form of least resistance. 
The following investigations will show, however, that the adoption of a form of least 
resistance, or of small comparative resistance, may, in fact, lead to a lavish outlay upon 
our ships, and to a great sacrifice of efficiency ; while, on the other hand, the adoption 
of a form of greater resistance would contribute in certain classes of ships to great 
economy and to superior efficiency. 
In order to indicate clearly, but approximately only, the purpose in view, I will first 
assume that figs. 1 & 2 roughly represent a long and a shorter ship respectively, both 
being prismatic in a vertical sense. The length of fig. 1 is seven times its breadth ; 
that of fig. 2 five times its breadth, the middle portion of the latter being parallel for 
two-fifths of its length. I will further assume that the ship (fig. 1) will give a constant 
of 600, and fig. 2 a constant of 500 in the Admiralty formula 
speed 3 x midship section 
• , =constant. 
indicated horse-power 
The draught of water is in each case 25 feet, and the total depth 50 feet. 
3 u 2 
