MECHANICS AND USEFUL ARTS. 25 



ship. In many cases the length of iron vessels was eight or nine times that 

 of the beam, and although he did not say that such had yet obtained their 

 maximum, length, yet the mode of construction was capable of much im- 

 provement. He assured them that vessels in a rolling sea, or stranded on a 

 lee-shore, were governed by the same laws of transverse strain as hollow 

 iron beams, like the Britannia tubular bridge; hence a ship could not be 

 lengthened with impunity without adding to its depth or the sectional area 

 of the plates in the middle. An iron ship of the ordinary construction 

 300 feet long, 4H feet beam, and 26 feet deqp was inadequately designed 

 to resist strains when treated as a simple beam; and a ship was like a sim- 

 ple beam when supported at each end by waves, or when, rising on the crest 

 of a wave, it was supported on the centre with the stem and stern partially 

 suspended. In these positions an iron ship underwent, alternately, a strain 

 of compression and a strain of tension along the whole section of the deck, 

 corresponding with equal strains along the keel. Such a vessel could make 

 a number of voyages at sea, because it was there sustained in a measure by 

 the water; but when driven upon a rock, with its bow and stern suspended, 

 it would break in two, owing to the insufficient mode of constructing the 

 decks. An iron ship of the foregoing dimensions, as usually constructed 

 and tried by the beam formula} W = (a d c -f- /), would be broken asunder 

 if tried with a weight of nine hundred and sixty tons suspended from bow 

 and stern. But if the deck-beams were covered with iron plates throughout 

 the whole length on each side of the hatchway, so as to render the deck area 

 equal to that of the bottom, we should have nearly twice the strength. He next 

 considered the displacement of such a vessel in tons, and found the strength 

 far from satisfactory. When loaded to a depth of eighteen feet, the displace- 

 ment was about one hundred and seventy -seven thousand cubic feet equiv- 

 alent to five thousand tons for the ship and cargo. If we considered this 

 weight uniformly distributed, and compared it with the strength determined, 

 we have a load uniformly distributed of five thousand tons added to that of the 

 breaking weight of the metal in the vessel, which would leave a deficiency of 

 strength equal to one thousand one hundred and sixty tons; so that, if laid 

 high and dry on a rock at the centre, it would break with four-fifths of the 

 load which it carried. These were extreme cases, but ships should be built 

 for them if possible. There had been improvements introduced recently in 

 iron vessels, still they were all too weak in the decks. These, he argued, 

 should be so strengthened as to be equal to the keel, and thus provide a 

 margin of strength for every contingency. He recommended the addition 

 of two longitudinal stringers, running one on each side of the keel; the cov- 

 ering of the cross-bearers of the upper deck with iron stringer plates, thick- 

 est towards the middle; also two cellular rectangular stringers one on 

 each side of the hatchway all running the whole length of the ship. He 

 also argued the importance of using the best quality of metal. No plates 

 should be employed that were incapable of withstanding a tensile strain of 

 twenty tons per square inch. 



Mr. J. Scott Russell pointed out various improvements which he had 

 carried out, especially with relation to water-tight bulkheads. These were 

 a source of great strength to iron vessels, as they were placed inside the 

 ship; and even if a collision took place, and the ship was cut through, they 

 would save it from sinking. Twelve years ago he built a vessel which 

 might be described as all bulkheads, and entirely divested of frames. Be- 

 lieving that the centre of the vessel required to be essentially strong, he 



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