98 MILITARY AND TECHNICAL CONSIDERATIONS 
Exact formulz for the influence of beam on speed do not exist, but model ex- 
periments seem to bear out the fact that on a given displacement for an increase 
of beam of, say, 5 per cent, the effective horse-power must be increased by the 
same percentage if the same speed is desired, and that if length be kept constant 
«IB t : i é : 
the ratio pcan be varied widely without any very appreciable effect on resistance. 
LENGTH. 
This dimension is influenced more by the speed than by any other feature of 
the design. In order to obtain high speed it is absolutely necessary to have length. 
To give a concrete example of this, assume that we desire 24 knots speed from a 
30,000-ton ship. With a 690-foot length the speed could be obtained with about 
40,000 horse-power. Keeping beam and draught constant, but shortening the length 
to 630 feet, there would be needed 50,000 horse-power, and at 570 feet over 80,000 
horse-power would be required; whereas, if we desire only 20 knots speed, it can be 
obtained on a 570-foot length with but little more than 40,000 horse-power. Fur- 
thermore, not only will the shorter ship require much more horse-power for a given 
speed, but it affords less length for the installation of the increased horse-power, 
so that practically the length must be great enough to enable the necessary machinery 
to be installed. 
On the other hand, by a too great increase in length we reach a point where 
the frictional resistance due to increased wetted surface is greater than the gain 
from reduced wave-making resistance, particularly at cruising speeds. Length is 
not favorable for maneuvering, increasing the resistance to turning. Length neces- 
sitates a serious increase in displacement, due to the greater weight of armor and 
hull for the same protection and same strength.* Greater length means greater 
target area, and incidentally there are but few dry docks that will accommodate great 
lengths. 
DISPLACEMENT. 
Many other features must be given their relative weight, the chief of which are 
seaworthiness, freeboard, and type of hull fittings, but enough has been said to in- 
dicate the principal military and technical considerations influencing and limiting 
battleship displacement. 
Passing over the more or less mechanical end of the calculations involved, it 
may be stated that, in the present state of the art of the naval architect and marine 
engineer, it is not possible to adequately fulfil these principal claims on less dimen- 
sions than 640 feet for length, 96 feet for beam, and 30 feet for draught, with a 
consequent displacement of approximately 36,000 tons. 
*If the same percentage of side is to be protected without decreasing the thickness of armor, the weight of 
side armor will increase directly with the length. The increase in hull weight is due to the greater area of 
plating, this area increasing approximately as the square root of the length, and also to the greater thickness 
of plating which it is necessary to use in order to provide adequate strength to meet the bending moment, 
which increases roughly as the length. 
