ON THE CONSTRUCTION OF IRON SHIPS. 695 
bilge-water which is always found in a wooden ship. Moreover, the use of 
iron masts, steel yards, and wire rigging effects a very large saving of weight, 
and affords the greatest facilities for the application of patent reefing sails 
and other appliances by which economy of labour is attained, and many risks 
of loss of human life avoided. 
As to the form of building iron ships, and the manner of combining the 
iron so as to obtain. the requisite amount of strength with the least amount 
of material, much difference of opinion exists amongst practical men. The 
angle-iron frame and plating of the iron vessel take respectively the places 
of the timbers and planking of the wooden ship; and it has been found by 
experience that plating sth of an inch thick is equivalent in effect to 
planking of oak one inch thick, while plating 14ths of an inch thick is equal 
to planking of oak 5 inches thick. As in the largest American wooden 
vessels the plank is seldom more than 5 inches thick, so it may be argued 
on the above data that the plating of the largest iron ship need not be more 
than 11ths thick; and that any strength required above that which such 
plating would give, should be obtained by means of framework. Many 
practical men, however, advocate the system of light framework, and, in order 
to obtain the measure of strength necessary, the application of thicker plates. 
That the principle of strong framing and plating of moderate thickness is 
most advantageous, may be shown by many facts other than those which 
are derived from the most modern practice of wood shipbuilding. The 
strength of an iron ship, as in a girder, depends on its capability to resist 
the buckling and tensile strains that it is called on to bear; but I believe 
that we have in reality only to make a ship strong enough to resist the 
buckling strain; and I am led to this conclusion by experiments conducted 
for that celebrated work, the Britannia Bridge, which proved that in con- 
structions of wrought iron the resistance to the tensile strain is much greater 
than the resistance to buckle, and, in consequence, the upper parts of the 
girders are made much stronger than the lower parts. We have, in my 
opinion, to make the parts of an iron ship, in principle, like a girder. A 
girder, however, is at rest and the strains are always in some known direc- 
tion; but in a ship whose position is ever varying, it requires to be so con- 
structed as to resist the strains in such varied positions. If the side of a 
ship could remain, as in a girder, constantly vertical, then the advocates for 
the thick plates and small frames might be able to show that their system 
was the most economical way to obtain the requisite strength ; but as such side, 
if laid over, as it is in a ship at sea, would, without support, bend or buckle 
of its own weight, it is evident that the framing is absolutely necessary to keep 
the plating firm in position, and consequently the strength of the ship de- 
pends in a very great degree on the strength of the framing. Another fact 
that shows the economy of strong frames, is that a plate, with a piece of angle- 
iron attached to its edge, would bear much more before buckling than a 
similar plate increased in thickness so as to weigh the same as the plate 
and angle-iron. But the great and most important argument in favour of 
moderately thick plates and strong framing is, that all the work must be 
put together by hand; for though many attempts have been made to rivet 
ships by machinery, none seem yet to have been successful even in a me- 
chanical point of view. So soon, therefore, as the thickness of plates and the 
size of the rivets pass the point at which the workman with ordinary ex- 
ertion can accomplish good work, then the attachment of the parts by means 
of riveting is subject to the risks of imperfect workmanship. It is, there- 
fore, my opinion, both in a practical and theoretical point of view, that we 
