THE “GREAT BRITAIN” (1843).
From the Model in the Victoria and Albert Museum.
PROPELLER OF THE “GREAT BRITAIN.”
From the Model in the Victoria and Albert Museum.
But apart from her size, the Great Britain possessed other novel features which are worthy of notice. We have already remarked that as the length of ships increased, so did the longitudinal strain, and new methods had to be devised in order to overcome this. The Great Britain was specially strengthened longitudinally, and furthermore she was divided into five water-tight compartments. The original purpose of transverse bulkheads was that if a vessel were holed by collision or grounding, or—in the case of naval vessels—pierced by shell, she might yet remain afloat. Nowadays they do more than this, for, when carried up to the strong deck, they add to the longitudinal strength of the ship. The Great Britain also possessed another novelty, in bilge keels, which extended for about one-third of her length. The object of these, which are so well-known a feature of modern steamships, was to lessen rolling. Her bulwarks consisted of iron rails with netting running round the ship. Here, again, was a new departure. In the older ships the heavy wooden bulwarks were a relic of the days when the guns were sheltered behind them; but from the view of seaworthiness they were really a false safety. If a heavy sea were shipped, the water was held in and not allowed to get away easily; in the case of the Great Britain the water could escape just as quickly as it came aboard.
[Facing page 128] will be seen a reproduction of a model of the Great Britain’s engines, as originally placed in her before she ran ashore. Steam was generated in a double-ended boiler. The nominal horse-power was 1,000, but twice that amount could be obtained, and a speed of over 12 knots. There were four direct-acting cylinders—of which two will be seen in the foreground of the illustration—placed as low down in the ship as possible. The early engines which were used for the screw did not drive the latter directly, and on reference to the illustration it will be seen that in the centre of the crank shaft was a drum, which was connected with another drum just below it on the propeller shaft by means of four chains.
When referring to the side-lever engines in a former chapter, I drew attention to the fact that in spite of their virtues they had the great drawback of taking up a great deal of space. [The second illustration facing page 128] represents an attempt to overcome this disadvantage. As will be seen on examining the lower part of the engines, the lever has now become very small in size. It will be noticed that there are two inverted cylinders, whose piston-rods are connected by a cross-head, the latter being guided by lever parallel movement, and from it the power was conveyed by means of a connecting rod to the crank on the paddle-wheel shaft. The connecting rod can be seen between the two cylinders in the illustration. These engines were made in 1843 for the Helen McGregor, a paddle-steamer engaged in the Hull-Hamburg trade. She was of 573 tons, and was one of the largest ships of her class.
