WEIGHT OE MATEEIAL IN THE CONSTRUCTION OF IRON-CLAD SHIPS. 485 
given speed of fourteen knots, while the breadth of the short ship slightly exceeds that 
of the long ship. But these differences in results are not greater than might have been 
anticipated from the adoption of such different forms of ships, and from the application 
to them of so different a rule for connecting speed with power. 
At the same time the investigation serves to show conclusively, that whether we 
adopt the theoretical best form of ship, and apply the most recent rule in our calcula- 
tions, or whether we guide ourselves by the practical trials of existing iron-clad ships, 
we in either case find that the speed of fourteen knots can be obtained in the short type 
of ship with surprisingly less size and cost than the long type of ship requires. 
It is easy to see how the difference between the horse-powers of the two curve-of- 
sines ships arises. The immersed surface of the longer vessel exceeds that of the shorter 
by 14669 sq. ft. At the speed of fourteen knots the frictional resistance per sq. ft. of 
surface =1*96 lb., and consequently the excess of this resistance upon the larger ship 
is 14669 X 1‘96 = 28810 lbs. This insistence has to be overcome through a distance of 
fourteen knots per hour ; and taking the effective work of one I.H.P. to be equal to 
200-knot lbs. per hour (which is the quantity used by Professor Rankine in his calcula- 
tion), we obtain 
I.H.P. expended in overcoming the excess of frictional resistance upon the larger ship 
28810 x 14 
200 
=2016-7 H.P., 
which corresponds very nearly to the difference between the engine-power of the two 
ships. As the immersed midship sections differ so little in the two cases, the difference 
of horse-power due to this course would obviously be very slight. 
It must be observed that the weight per sq. ft. of hull has been taken the same for 
both curve-of-sines ships, whereas an increase would be necessary for the larger ship. 
I omit this correction as it would lead to a cubic equation ; but it would obviously 
enhance the size and cost of the larger ship, and thus exhibit the advantage of th e shorter 
ship in a still clearer light. 
