The screw engines, of 1,600 nominal horse-power, consist of four fixed horizontal cylinders, 4 feet stroke and 7 feet diameter, the two cylinders of each pair working opposite to each other on one crank.
In each boiler room are two donkey engines for supplying the boilers with water, and the main engines are also fitted with feed-pumps. Each of the donkey engines is capable of pumping water out of the ship, and of being used in case of fire.
The screw shaft passes along what is termed a screw alley (P). The weight of the screw rests on the bearing where the screw shaft passes out through the stern-post of the ship. To prevent the water that leaks in through this bearing from penetrating into the screw alley, there is a bulkhead with a stuffing-box round the screw shaft, a short distance forward of the stern-post. To enable access to be gained to the bearing, a tube was provided leading down from the main-deck. This was intended to be fitted with appliances for pumping air in so as to drive the water out, and to admit men to get at the bearing under air pressure.
Another arrangement was also provided for the same purpose. On the after side of the stern-post was placed a ring of india-rubber; and, by pulling in the screw-shaft, the screw was pressed tightly against the india-rubber ring, which prevented the water from entering. By means of this arrangement the stern-bearing was examined and repaired at Southampton.
The screw propeller has four blades, and is 24 feet in diameter and 44 feet pitch. The paddlewheels were 56 feet in diameter, with 30 floats, each 13 feet broad and 3 feet deep.
Over the boiler rooms run two tunnels; one of them (V) serves as a passage to enable the engineers to pass from one compartment to another throughout the part of the ship occupied by the boilers and engines. The openings leading from the tunnel to the engine or boiler rooms are provided with watertight doors, which can be shut in the event of any of the compartments getting full of water. The other tunnel (W) serves as a passage for the steampipe, which leads from the boilers to the engines. Though the boilers are divided into two sets, one for the paddle engines and one for the screw, the steampipes are connected, so that the whole of the ten boilers, or any of them, may be used to supply steam for either of the engines.
In one point a deviation was made from Mr. Brunel’s arrangements. It was his intention that there should be no apertures in the water-tight bulkheads except at the tunnel (V), from which the various boiler and engine rooms were to be entered by openings, to be closed by water-tight doors. The tunnel was placed high up, so that in the event of a leak there might be ample time to close the door. The inconvenience of ascending and descending by ladders was, however, considered an evil; and it was found necessary at times to carry coals from one compartment to another. For these reasons, upon the requirement of the Board of Trade, doorways, fitted with sliding doors, which can be closed by handles on the upper deck, have been cut in the bulkheads between the boiler rooms. This arrangement exists in other ships; and in the ‘Great Eastern,’ even without closing these doors, there are eight watertight compartments.
At the stern of the ship (Y) on the main-deck are arrangements for working cables, similar to those at the bow.
These appliances are required when the ship has to be moored so as not to swing with the tide; and they would allow of the ship’s riding by the stern instead of by the bow, which it might often be useful for her to do in narrow waters. On the lower deck (Y), at the stern of the ship, is a spare tiller and wheel for working the rudder, in case anything goes wrong with the main tiller, which is on the upper deck. The weight of the rudder is carried on the lower deck by a grooved collar, resting on a ring of cannon balls.
The compartment (X) immediately aft of the screw engine room is for cargo.