SHIPS BUILT OF IRON AND STEEL
Even before the introduction of steam as a motive power for boats shipbuilders had been casting about for some satisfactory substitute for wood in the construction of vessels. One reason for this was that suitable wood was becoming scarce and very expensive. But also there was a limit to the size that a wooden vessel might be built with safety. A wooden boat more than three hundred feet long cannot be constructed without having dangerous structural weakness.
Naturally the idea that the only suitable material for boat-building was something lighter than water,—something that would float—which had been handed down traditionally for thousands of years, could not be overcome in a moment. And surely such a heavy substance as iron would not be likely to suggest itself to the average ship-builder. But at the beginning of the nineteenth century rapid strides were being made in theoretical, as well as applied science, and the idea of using metal in place of wood for shipbuilding began to take practical form.
Richard Trevithick, whose remarkable experiments in locomotive building have been noted in another chapter, had planned an iron ship as early as 1809. He did not actually construct a vessel, but he made detailed plans of one—not merely a boat with an iron hull, but with decks, beams, masts, yards, and spars made of the same material. It was nearly ten years after Trevithick drew his plans, however, before the first iron ship was constructed. Then Thomas Wilson of Glasgow built a vessel on practically the same lines suggested by Trevithick.
This vessel, finished in 1818, and called the Vulcan, was the pioneer of all iron boats. For at least sixty years it remained in active service. Indeed, for aught that is known to the contrary, this first iron boat may be still in use in some capacity.
One of the most surprising and interesting things to shipbuilders about the Vulcan, and the boats that were constructed after her, was the fact that they were actually lighter in proportion to their carrying capacity than ships of corresponding size built of wood. In wooden cargo ships the weight of the hull and fittings varies from 35 to 45 per cent. of the total displacement, while iron vessels vary from 25 to 30 per cent. This was a vital point in favor of the iron vessel, and one that appealed directly to practical builders. But the public at large looked askance at the new vessels. To "sink like a stone" was proverbial; and everyone knows that iron sinks quite as readily as stone.
But very soon a convincing demonstration of the strength of iron vessels brought them into favor. A great storm, sweeping along the coast of Great Britain in 1835, drove many vessels on shore, among them an iron steamboat just making her maiden voyage. The wooden vessels without exception were wrecked, most of them destroyed, but the iron vessel, although subjected to the same conditions, escaped without injury, thanks to the material and method of her construction.
From that time the position of the iron steamship was assured. And whereas sea voyagers had formerly looked askance at iron passenger boats they now began to distrust those built of wood. By the middle of the century, iron shipbuilding was at its height, and in the decade immediately following, the Great Eastern was finished—possibly the largest and most remarkable structure ever built of iron, on land or sea. In recent years larger ships have been constructed, but these ships are made of steel.
The Great Eastern marked an epoch in shipbuilding. In size she was a generation ahead of her time, but the innovations in the method of her construction gave the cue to modern revolutionary shipbuilding methods. Sir George C. V. Holmes gives the following account of the great ship:
"She was originally intended by the famous engineer, Mr. I. K. Brunel, to trade between England and the East. She was designed to make the voyage to Australia without calling anywhere en route to coal, a feat which, in the then state of steam-engine economy, no other vessel could accomplish. It was supposed that this advantage, coupled with the high speed expected from her great length, would secure for her the command of the enormous cargoes which would be necessary to fill her. Mr. Brunel communicated his idea that such a vessel should be constructed for the trade to the East to the famous engineer and shipbuilder, the late Mr. John Scott Russell, F.R.S., and he further persuaded his clients, the directors of the Eastern Steam Navigation Company, of the soundness of his views, for they resolved that the projected vessel should be built for their company, and entrusted the contract for its execution to the firm of John Scott Russell & Co., of Millwall.
"Mr. Scott Russell and Mr. Brunel were, between them, entitled to the credit of the design, which, on account of the exceptional size of the ship, presented special difficulties, and involved a total departure from ordinary practice.
"Mr. Scott Russell had systematically, in his own previous practice, constructed iron ships with cellular bottoms, but the cells had only five sides, the uppermost side on the inside being uncovered. Over a large portion, however, of the bottom of the Great Eastern the cells were completed by the addition of an inner bottom, which added greatly both to the strength and to the safety of the ship. It was also Mr. Brunel's idea that the great ship should be propelled by both paddles and screw. Mr. Scott Russell was responsible for the lines and dimensions, and also for the longitudinal system of framing, with its numerous complete and partial transverse and longitudinal bulkheads.
"The following are some of the principal dimensions and other data of the Great Eastern:
| Length between perpendiculars | 680 | feet |
| Length on upper deck | 692 | " |
| Extreme breadth of hull | 83 | " |
| Width over paddle-box | 120 | " |
| Depth from upper deck to keel | 58 | " |
| Draught of water (laden) | 30 | " |
| Weight of iron used in construction | 10,000 | tons |
| Number of plates used in construction | 30,000 | |
| Number of rivets used in construction | 3,000,000 | |
| Tonnage, gross | 18,914 | tons |
| Nominal power of paddle engine | 1,000 | H. P. |
| Nominal power of screw engines | 1,600 | " |
"The accommodation for passengers was on an unprecedented scale. There were no less than five saloons on the upper, and as many on the lower deck, the aggregate length of the principal apartments being 400 feet. There was accommodation for 800 first-class, 2,000 second-class, and 1,200 third-class passengers, and the crew numbered 400. The upper deck, which was of a continuous iron-plated and cellular structure, ran flush from stem to stern, and was twenty feet wide on each side of the hatchways; thus two spacious promenades were provided, each over a furlong in length. The capacity for coal and cargo was 18,000 tons.
"The attempts to launch this vessel were most disastrous, and cost no less than £120,000, an expense which ruined the company. The original company was wound up, and the great ship sold for £160,000 to a new company, and was completed in the year 1859. The new company very unwisely determined to put her on the American station, for which she was in no way suited. During her preliminary trip the pilot reported that she made a speed of fully 14 knots at two-thirds of full pressure, but the highest rate of speed which she attained on this occasion was 15 knots, and on her first journey across the Atlantic the average speed was nearly 14 knots, the greatest distance run in a day having been 333 nautical miles. The great value of the system adopted in her construction was proved by an accident which occurred during one of her Transatlantic voyages. She ran against a pointed rock, but the voyage was continued without hindrance. It was afterwards found that holes of the combined length of over 100 feet had been torn in her outer bottom; but, thanks to the inner water-tight skin, no water was admitted."
Between the years 1860 and 1870 great improvements were made in marine engines, and screw-steamers very generally replaced side-wheel boats for ocean traffic. The improvements in the engines consisted largely in the use of higher pressures, surface condensation, and compounding of the cylinders, which resulted in a saving of about half the amount of fuel over engines of the older type. As a result steamers were able to compete successfully with the sailing ships, even as freighters for long voyages, such as those between Europe and Australia.
During the reactive period in France immediately following the Franco-Prussian war, when there was great activity in shipbuilding, the use of mild steel plates in place of wrought iron was tried. The superiority of this material over iron was quickly demonstrated, and as the cost of steel was constantly lessening, thanks to the newly discovered methods of production, steel practically replaced iron in ship construction after this time.
It was during this same period that a new type of passenger steamer was produced—the "ocean greyhound." The first of these was the Oceanic, built by the White Star Company in 1871. This ship was remarkable in many ways. Her length, four hundred and twenty feet, was more than ten times her beam; iron railings were substituted for bulwarks; and the passenger quarters were shifted from the position near the stern to the middle of the vessel. All these changes proved to be distinct improvements, and the Oceanic became at once the most popular, as well as the fastest ocean liner.
Like all the other boats of the seventies and early eighties, the Oceanic was a single-screw vessel. The advantage of double propellers in case of accident had long been recognized, but hitherto twin-screws had not proved as efficient as a single screw in developing speed. But in 1888 the City of Paris (now the Philadelphia) a twin-screw boat, began making new speed records, and the following year her sister ship, the New York, and the new Majestic and Teutonic, entering into the ocean-record contests, cut the time of the passage between Europe and America to less than six days.
The advantages of the double-screw over the single are so many and so manifest as to leave no question as to their superiority. The disabling of the shaft or screw of the single-screw steamer, or the derangement of her rudder renders the vessel helpless. Not so the twin-screw ship; for on such ships the screws can be used for steering as well as propelling. And it has happened many times that twin-screw ships have crossed the ocean with the steering gear disabled, or with one screw entirely out of commission.