The conditions under which the riveting in cellular and bracket bottoms is accomplished are less favourable to expeditious work. This system of ship’s bottom is greatly more complex in its constructive features than the ordinary bottom. The separate plates and angles which go to form the bracket floor system are to be numbered—in vessels of the average size—by thousands. The frames in such vessels are formed of three parts; one part stretches across the bottom and abuts against the plates forming the sides of the cellular bottom; the other two parts form the sides of the vessel, but are not erected until the bottom portions of the frames have been laid and all the bracket and longitudinal girders are erected and fitted upon them. On the bottom, as thus described, the portable riveters are required to operate, in many instances having to reach the rivets at a distance of 4 feet 6 inches from the edge of the plates, and in confined spaces of 24 inches. When the frames and beams are completely riveted and beginning to be erected, a travelling-crane (in Messrs M‘Millan’s two travelling cranes are employed working from separate ends of the vessel) carrying a large portable riveter, is placed on the top of the floors, with short lengths of planking laid to act as tramways. The perfect control thus obtained is somewhat extraordinary. The crane jib has sufficient rake to command the whole floor of the ship, and every rivet can be closed in the confined spaces already described. Some 800 rivets per day can be put in, many of them at a distance of 4 feet 6 ins. from the edge of the plate. The quality of the work is all that could be desired; in some parts, indeed, the use of the felt-packing necessary in hand work has been found to be unnecessary owing to the tight work obtained by hydraulic riveting. One crane with its riveting machine can, in a vessel of moderate size, say 3,000 to 4,000 tons, fully keep pace with the up-ending of the frames, provided it has something of a start. As it advances the lower deck beams are put in place behind it, and the other work follows in order. In ships of the more ordinary construction, longitudinal keelsons are fitted, which are readily reached by special portable riveters, suspended by means of neat devices, some of them the ideas or suggestions of workmen in Messrs M‘Millan’s service.