Many minor, yet aggregately important, structural features which are products of the progressive movement of recent years, or are simply revivals of old devices which were “untimely born,” still call for some notice. As a necessary consequence of the growth in dimensions and the change in relative proportions of vessels, greater regard has been paid to the systems of construction in which the longitudinal principle is involved. This, of course, is evidenced by what has been said of the cellular bottom system, but various minor structural features associated with the cellular bottom are also noteworthy in this connection. It is the practice, for instance, where large ships are concerned, to fit side stringers in the holds, throughout the entire length, made intercostal with regard to transverse plate or web-frames occurring at intervals of 16 or 20 feet, which extend from the bilge to the main deck. This arrangement—an outline of which may be found to the right of the section shown as Fig. 1—possesses many structural advantages, and finds additional favour with shipowners on account of its leaving a clearer hold for stowage by obviating the use of transverse hold beams.
Regard for transverse strength has increasingly evinced itself in the fitting of various kinds of plate side stiffeners or partial bulkheads. This is well exemplified in a very recent case—that of the National Company’s steamship America, built by Messrs J. & G. Thomson. This vessel, having been constructed independent of any special Registry Rules, embodies structural features not common amongst vessels in which such rules are undeviatingly conformed to. The system referred to, of plate frames or partial bulkheads, is one of the most conspicuous of these features. Throughout the length of the vessel, at intervals of about 18 feet, transverse plate stiffeners or frames, extending from the shell inwards about 4 feet, take the place of the ordinary angle frames, and are continuous from floors to upper deck, the stringers and other longitudinal features being scored through them. The surplus transverse strength resulting from this system is such as amply to compensate for uncommonly large breaches made in the deck beams and plating for light and air purposes in the saloons. This is a very special feature in the interior arrangement of the America, and will be referred to further on. The regard for transverse strength, again, conjointly with the increased attention to minute watertight sub-division, has led to the fitting of a greater number of complete watertight transverse bulkheads, relatively to the lengths of vessels.
In vessels of extreme proportions the method of forming shells two-ply, or of fitting all the shell plates edge to edge with outside covering-strakes over the fore-and-aft joints, has been recently revived and much improved. The system, although very expensive, has been adopted in vessels for the Anchor Line by Messrs D. & W. Henderson, Glasgow, and subsequently on even a more extensive scale by the Barrow Shipbuilding Company.
Affecting the structural character of modern ships very materially, but the result chiefly of an economy in labour, riveting by machine power has received a wonderfully extended application within recent years. Structurally, as well as commercially, the system has played a large part in the progressive movement under review. By its means the strength of united parts has been enhanced through the increase of their frictional resistance, and through the rigidity of joints, due to the more thorough filling of the rivet holes. The subject of hydraulic or machine power riveting will, however, receive fuller treatment in a subsequent chapter.
Within the past two or three years cast steel stems, stern-frames, and rudders, have been taking the place of forged iron work in ship construction. The practicability of manufacturing these of such strength and homogeneity as would meet the needs of ship construction even better than the ordinary forged work, had occurred some five or six years ago to several engaged in the steel trade. Mr J. F. Hall, of Messrs William Jessop & Sons, Limited, Sheffield, had the subject under consideration about that period, and actually made several small stern posts and rudders for steam yachts and launches. The advantages of solid and uniform steel castings over iron forgings—which, with their many weldings, so often prove inefficient when subject to any sudden shock—were even then rightly enough appreciated. It was only, however, after patents had been taken out by Messrs Cooke & Mylchreest, of Liverpool, for various devices connected with the actual fitting of such features to the ship’s structure—amongst other things the hanging of rudders without pintles or gudgeons—that the manufacture of cast steel stern-frames, rudders, &c., was seriously proceeded with.
In July, 1882, the Steel Company of Scotland (Limited), who are the manufacturers in Scotland of Messrs Cooke & Mylchreest’s patent form of rudders and stern-frames, successfully cast a stern-frame—the first of large size, it is believed, made for actual use in the construction of a steamer. In April of the same year, however, Messrs William Jessop & Sons (Limited), of Sheffield, had exhibited a crucible cast steel stern-frame and rudder of their manufacture, at the Naval and Sub-Marine Exhibition, held in London. These large castings, along with others, were subjected to a series of tests in the presence of Lloyd’s inspectors and other authorities, such as the forged frames and rudders ordinarily fitted would not have come through without severe damage, yet all of which the steel castings withstood most thoroughly.
Testimony to the efficiency of these new features in ship construction has already been furnished from the arena of actual experience, by the recent grounding of two steamers in which these features had been introduced. The screw-steamer Euripides, a Liverpool-owned vessel of about 1780 tons gross, completed in May, 1883, by Messrs Caird & Purdie, of Barrow, some time ago ran upon a reef of boulders, and remained thumping heavily for several hours. At the time she was laden with a full cargo of grain, which was afterwards delivered in perfect condition. The cast steel stem and stern-frame, which were manufactured by the Steel Company of Scotland, were practically without damage, notwithstanding that serious indentations were made in them. The stem, although receiving the full force of resistance, was not perceptibly altered in shape, and competent judges who inspected the damage in dock were of opinion that the stem, with its superior attachments, in all probability saved the vessel from total loss. The rudder on the Euripides is of solid cast steel, in one piece, and hung without pintles, and in a manner involving little or no riveting. In this, as in the other features, the immunity from serious damage testifies to the efficiency and durability of the steel castings. The second case of grounding referred to is that of the screw-steamer Strathnairn, of 400 tons, belonging to Messrs James Hay & Sons, of Glasgow; one of two vessels built by Messrs Burrell & Son, of Dumbarton, in which cast steel stern-frames and rudders were adopted. This vessel got aground while off Harrington, on the north-west coast of England, about the latter end of March of the present year. Her stern-frame sustained very considerable shock: such, indeed, as no ordinary forged work could possibly have undergone with like result. Subsequent docking showed that it would only be necessary to straighten the frame at the deflected portions in order to make it again structurally efficient. This was done, and the vessel is again actively engaged in service.