Fig. 13. ‘Great Britain’ Steam-Ship. _Transverse Section._] She had no keel, as there did not appear to be sufficient advantage gained by such an appendage to make up for the increase of the ship’s draught by the amount of the depth of the keel. There were two side or bilge keels (_e_), reaching down to the level of the keel plate of the ship, so that when grounded in dock she might rest on three points in her width. The ‘Great Britain’ had what is termed a balanced rudder, a portion of the rudder (in this case about one third) being in advance of the pivot on which it turned. The result of this arrangement was that, the pressures on either side of the pivot nearly balancing one another, there was no difficulty in putting the helm over rapidly. This rudder was knocked away when the ship ran ashore at Dundrum, and was subsequently replaced by an ordinary rudder.[131] In the construction of the hull of the ship, instead of a mere imitation of the arrangements of the timber in wooden ships, the proper distribution of the material to receive the strains that would come upon it was carefully considered. In the result, the ship contained, in the structure of her bottom, bulkheads, deck shelves, and longitudinal kelsons, the longitudinal principle of construction which Mr. Brunel afterwards so fully developed in the ‘Great Eastern.’ Apart from their size, the design of the engines of the ‘Great Britain’ necessarily presented many peculiarities. The boilers, which were six in number, were placed touching each other, so as to form one large boiler about thirty-three feet square, divided by one transverse and two longitudinal partitions. This boiler, which was fitted in between the longitudinal bulkheads of the ship, had a double set of furnaces, and therefore of stoke-holes, one at the fore end, and the other at the after end, next the engine room. It would seem that the boiler was only worked with a pressure of about eight pounds on the square inch. The feed water for the boiler was passed through a casing surrounding the funnel, in which it was heated before passing into the boiler. This casing was open at the top, and the water flowed thence into the boiler by gravitation. A similar arrangement was adopted by Mr. Brunel in the ‘Great Eastern.’