I am now going to give you the structural details of the ship now building by me at my works at Port-Glasgow. I shall beg your particular attention in any other ship that has yet been built.
The frames or ribs of this ship, which constitute the main support of the ship, run in an oblique direction from the starboard gunwale down the side and across the keel, to which they are firmly united by an intercostal keelson and four sister keelsons, these continuing their obliquity up by the opposite side to the larboard gunwale. The poop and forecastle beams are secured to one frame on the starboard side, and to a different frame on the port side. The main deck beams are also fixed to different frames, and also the lower deck beams; that is, the end of the main deck beam is secured to on frame on the starboard side running forward, and to a perfectly different frame on the port side running aft, which frames, being placed diagonally reverse to each other, are 28 feet apart at the gunwale, but joined together at the keel, by which means almost every beam is fastened to a frame, and the floors are likewise fastened to the frames, so that the ship forms a complete network of iron, embracing diagonal and vertical combinations of structural stability amounting to double that of the present mode of building iron ships. Before this ship can break in two parts or tear her plating asunder, she must break through 20 frames of angle iron 4½ by 3 by ½ inches, as well as 10 frames of angle iron 3 by 3 by 7/16; whereas in a ship built on the vertical principle the poop and main and lower deck beams are secured to one frame only on the starboard and port sides, and they are three feet apart at least, which leaves every alternate frame unsustained by any beam at all, so that on the application of any force to produce a rupture in a vertical line there is not a single frame interposing to resist the rupture from the keel to the gunwale. The outside plates are 11/16 and ¾-inch thick in all parts when so required by Lloyds'. She is divided vertically by four watertight bulkheads half an inch in thickness, and these are strengthened by diagonal stays or bars; and, having a deck of iron besides one of timber, she is, so to speak, a hollow tubular girder to the Britannia Bridge, with this exception, of course, that the bridge is a flat structure, whilst the bottom of this ship is an inverted arch, which is acknowledged to be a necessary form for the bottom of a ship.
Let us now turn our attention to the experiment, made with the most scrupulous fidelity, to test the strength of this diagonal principle so adopted by me. [page 5]
Two models were constructed for this purpose, one to represent the present vertical mode of building, and the other to represent my patented diagonal principle. In all other respects the models were precisely similar, each having an elastic keel to admit of a proper distribution of the strain, which each structure rested on a fulcrum intended to indicate the position of a rock or sand-bank under its keel. The result of this experiment proved that, whilst a ship built according to the ordinary plan would be torn asunder vertically through her plating, or, as the phrase is, "break her back," and break in two, a ship built on my patented diagonal principle would resist a strain from more than double the amount of force without any injurious effect whatever; and, in the experiment referred to, the model representation of the principle was not even twisted by the great amount of strain upon it. (See Mr. Thornston's Report appended, page 9.)
Suppose a ship to rest upon a fulcrum in the centre of its keel, and equal weights to be placed at each extremity with a tendency to tear the ship asunder vertically amidships, as shown in the accompanying plate, then —
To tear asunder a ship built on the vertical principle, size and weight of metal being the same as Taylerson's, a strain would be required equal to 11,610 tons weight at each end, whereas —
A ship on Taylerson's diagonal principle would bear a strain equal to a weight of 23,152½ tons without any injurious effect upon the vessel. See plates 1 and 2.
These calculations are based on the strength of iron structures as ascertained by experiments in the construction of the Menai Bridge and other works of great magnitude, and the arrangement and distribution of material in ships built upon the vertical and diagonal principles respectively; and they clearly demonstrate that no ship built on the vertical or longitudinal principle can bear anything like the same amount of pressure or strain as that which might be borne without injury by one constructed on Taylerson's patented diagonal principle.
(Signed) Robert Thornton, C. & P.E.
St. Leonard's Iron Works, Edingburgh, 15th November, 1858.
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