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.
The only machine of the series of portable riveters employed by Messrs M‘Millan which remains to be noticed is that which overtakes the riveting of keels. This machine is perhaps one of the most perfect of the series, performing its functions satisfactorily, viewed from whatever standpoint. The riveting required on the keel of large vessels is very heavy, especially if the through-keelson and side-bar system is adopted, when five thicknesses of plate have to be connected, the rivets employed being 1⅛-inch or 1¼-inch in diameter. The situation is not favourable for getting at the work to be done, the head-room available not often exceeding 2½ or 3 feet. These conditions render great compactness, together with portableness, necessary in the machine. The keel itself was utilised for the attachment of the Tweddell riveter as first tried, then again a sort of light trestle was employed, the riveter being at one end of a lever racking on this. These plans were abandoned, however, in favour of the machine as now used in various yards throughout the country, an illustration of which is given by Fig. 23. A low carriage is travelled down alongside the keel. This carriage supports a balanced lever, carrying at one end the riveter, capable of exerting about 50 tons on the rivet head, and at the other a balance weight. This lever can in its turn revolve horizontally about a short pillar fixed on a turn-table, thus affording unlimited control over the riveter by the man in charge; enabling him, indeed, to adjust the riveter to every irregularity of position or direction of the rivets in keel. As many as 420 1¼-inch rivets per day have been put in by this machine, an amount which is fully equal to the work of two squads of riveters, and in one yard 70 rivets have been closed in as many consecutive minutes.
FIG. 23.
TWEDDELL HYDRAULIC KEEL RIVETER.
It may be stated generally that the several hydraulic riveters require two men to work them, and the rivets are heated in portable furnaces and dealt out in any quantities required, by a boy in attendance. The quality of the work done is superior to hand work, chiefly in that when rivets are well heated the pressure is equalised, and affects the rivets throughout their entire length, filling the holes to their utmost. This advantage tells more in the case of keel riveting, and that it is so is evidenced by the fact, as communicated by a foreman having great experience, that rivets ¼-inch longer than rivets closed by hand have even less superfluous surface material when closed by the machine.
From the facts above detailed, taken in conjunction with the opinions of such authorities as Mr West, it can fairly be claimed for Mr Tweddell as the inventor of the earliest of the hydraulic riveters now so extensively employed in shipyards, that he has greatly improved the character of work in ship construction. Not only so, but he has relieved the shipyard artizan from a species of work which requires little or no skill in its execution—work, indeed, which may properly be relegated to, as it certainly in course of time will be included in, that vast domain in which water, steam, electricity, and the other natural powers are so wondrously made to play their part.
While the extended use of improved machinery has brought about changes in the iron-working departments of shipyards that are structurally of the greatest importance, it is nevertheless true that the largest acquisition to shipyard machinery of late has been made in the wood-working departments. It is here, beyond question, where the equipment of modern shipyards is seen to be so much an advance on the former order of things, when handicraft was indispensable and paramount; and it is also here, probably, where the greatest labour-saving advances have been made. The artistic perfection which is evinced in the palatial saloons and state-rooms of many modern steamships would not have been possible—commercially so, at least—to the shipbuilders of twenty years ago, whose appliances, regarded from present-day standpoints, seem to have been woefully crude and meagre. Still, it is not by any means to be understood that all the shipyards of to-day are alike commentaries on the former state of things, because even now there are not wanting yards in which the necessary wood-work for ships is accomplished with singularly few machines. The need for accessions in this direction, however, is being more keenly felt every day, and in many yards quite recently the entire joinery department has been thoroughly re-organised and equipped. The chapter which follows will be devoted to descriptions of some representative establishments in the several districts, and as special references may therein be made to the machinery equipment of the wood-working departments, the present remarks will only be of a general nature.
The conversion of wood from the absolutely rough state into finished and finely-surfaced material, ready for immediate use in the interior of vessels, forms at the present time not an uncommon portion of the daily work in shipyards well equipped with modern machinery. This is not only concerned with the commoner woods employed in large quantities for structural purposes, but also to a considerable extent with those various ornamental hardwoods entering into the decorative features. The change of which this is indicative is one of increased self-dependence and economy formerly not dreamed of in shipyards, and of improvements at every stage in the machinery for wood conversion, which are simply wonderful. In circular and straight saws, planing, moulding, and shaping machines, band and fret-saw machines, mortising, tenoning, and dove-tailing machines, and in machines for scraping, sand-papering, and miscellaneous purposes, not a few modern shipyards reflect the fullest engineering progress as concerned with wood-working machinery. In planing machines especially are the labour-saving advantages made apparent. As illustrating this it may be explained that machines of this kind in daily use are able to plane a greatly increased breadth of surface, to work several sides of the wood at one operation, and at a marvellously accelerated speed as compared with hand work. Similarly, as regards the formation of mouldings, it may be stated that a moulding which would take a competent workman some hours to produce can be completed on a good machine in less than one minute. Many patterns of mouldings and other decorative items now largely used are thus only possible—commercially if not otherwise—through the extended employment of machinery. The degree of “finish” now put upon the plainest features—rendered pecuniarly possible by the use of machinery—is nowhere so striking as in the scraping of panels and the sand-papering of large surfaces. In one shipyard the author has witnessed the scraping of hardwood panels as broad as 30-ins., the shaving taken off being of marvellous thinness and perfectly uniform and entire throughout the length and breadth of panel. The surface left on the panel is beautifully smooth, rendering any after-dressing with sand paper superfluous, and the shavings have all the appearance and much of the flexibility of fine paper. In many other ways that might be instanced, the improvement in machinery is not less striking, but what has already been given may sufficiently illustrate the general advance.