Modern shipbuilding and the men engaged in it

by David Pollock

This shows in section the bottom part of a vessel amidships, fitted with a double or inner skin, extending across the ship from bilge to bilge, and there connected in a watertight manner to the outer bottom plating. A series of longitudinal plates are worked, fore and aft; set vertically between the outer skin of the vessel and the plating of the inner bottom, and connected thereto by continuous angles. Between these “longitudinals,” and at every alternate transverse frame, deep plate floors, lightened with oval holes, are fitted, connected to outer skin by the angle frame, and to inner bottom plating by pieces of angles corresponding to the vessel’s “reverse frames.” These floor plates are, in addition, connected by vertical angles to the longitudinals. Intermediate between the deep plate floors simple angle bar transverse frames and reverse frames are fitted, to give support to the outer skin and to the inner bottom respectively. Until recently, the deep floors consisted of “gusset” or “bracket” plates, each division being fitted in four separate pieces, the whole taking the form as shown in dotted outline. This practice is still most largely followed, but in those yards which are equipped with large hydraulic punching machines for piercing holes such as are shown in Fig. 1, the solid floors have superseded the bracket or four-piece floors, the change effecting a simplification of work and decided structural advantages.

With the employment of water as a substitute for dry or rubble ballast, the structural movement under notice may be said primarily to have begun. This movement has resulted in the present approved system, which, at the same time that it has regard to water-ballast with all its attendant advantages, most happily combines the important qualities of increased strength and security. The need for ballast in vessels whose service generally comprises “light” as well as “loaded” runs (as in the coal trade between Newcastle and London), or in trades where the full complement can only be obtained by shifting from port to port, is obviously great. It is doubtless to needs such as these, more than to any demand for increased structural strength, that the introduction and extended application of the longitudinal and bracket-plate principle is owing.

The screw-steamer Sentinel, built in 1860 by Messrs Palmer of Jarrow, Newcastle-on-Tyne, is mentioned by some authorities as embodying some of the main features of the longitudinal and cellular bottom system, and the screw-steamers Scio and Assyria, of 1440 tons, built in 1874 by Messrs Westerman, near Genoa, have been noticed in a similar connection. The next vessel, in point of time, which contained features answering to the system now in vogue, and from the date of whose production the movement has been almost constantly progressive, was the screw-steamer Fenton, built by Messrs Austin & Hunter, of Sunderland, in 1876.

Clyde builders were not slow to recognise the value of the system in its application to water-ballast steamers, and almost immediately some of the more intrepid of their number began to advocate its adoption, but with some modifications, in vessels then being contracted for. Mr John Inglis, jun., of Messrs A. & J. Inglis, Pointhouse, Glasgow, submitted to Lloyd’s Registry in March, 1878, the scantling section of some cellular bottom vessels, then in project, which contained several of the improvements introduced in subsequent practice. Messrs William Denny & Brothers, of Dumbarton, at the same time took up the principle, and have since actively applied it to steamers of every character in which water-ballast is a desideratum. Adopting it, five years ago, in four sister vessels for the British India Steam Navigation Coy., they subsequently raised the important issue with the Board of Trade regarding the tonnage measurement of these vessels. This august body insisted on computing the register tonnage—the figure upon which the tonnage dues are levied—not to the top of the inner bottom, but to an imaginary line half-way down the cellular space—in fact, to where the line of floor would have been if constructed in the ordinary fashion. Messrs Denny maintained, in effect, that as the register tonnage was meant to be a measure of the space available for cargo, the top of the ceiling on the inner bottom was the only equitable line of measurement. The principal reason for the Board seeking to pursue this course seems to have lain in the supposition that owners would endeavour to use the double bottom for cargo-carrying purposes. An ambiguity in the words of the Merchant Shipping Act, or their inapplicability to present day practice, were other possible elements in the case, but doubtless the red-tapeism and self-sufficiency characteristic of the Board had much to do with their action. This is borne out by the fact that although the Messrs Denny succeeded in their plea with respect to vessels having structural cellular bottoms, the absurd practice is still followed in cases where the bottom is fitted for water ballast on the girder principle, i.e.—the inner bottom fitted upon fore and aft runners or girders, erected on floors of the ordinary description, as shown in Fig. 2.

FIG. 2.

This formed, and still forms in many places, a very common arrangement for water ballast steamers, although not so inherent a feature of the vessel’s structure as the continuous-cellular bottom. In most cases this system is fitted only for part of the length, and not, like the cellular system, applied throughout the whole length of the ship. If it was impossible for the Board of Trade to hold by the contention that cargo might be carried in bottoms of the structural cellular type, it is equally untenable in the case of bottoms such as are now referred to. The difference between the two kinds of ballast bottoms is one merely of construction, and if any one of the two lends itself to cargo-carrying purposes, it is certainly the cellular system. The anomaly is sufficiently striking to merit attention, and in certain districts where the girder system is largely adopted for medium-sized vessels, it is felt as nothing short of an injustice, both by shipowners and builders.

The concession or victory won by Messrs Denny removed a serious hindrance to the spread and general adoption of the water ballast cellular system. Other Clyde firms at the same time—or at least soon after the adoption of the system by the Messrs Denny—took the matter up and independently did much towards the popularisation of the cellular mode of construction. Speaking in the early part of 1880, Mr William John, of Lloyd’s Registry, now General Manager with the Barrow Shipbuilding Company, said:—“At the time Mr Martell read his paper on water-ballast steamers before the autumn meeting of this Institution (Naval Architects) at Glasgow, in 1877, there had been only two or three small steamers built (since Mr Scott Russell’s early ones) on the longitudinal principle. Now, it is within the mark to say there are one hundred steamers, built and building, whose bottoms are constructed on the longitudinal principle, or what is better described as the cellular system, amounting probably to 200,000 tons, and it is not outside the bounds of probability that a very few years will see the majority of merchant steamers constructed in this manner.” Mr John’s connection with Lloyd’s at the time, entitled his statements and opinions with regard to the prevalency and prospects of cellular construction to be accepted with every assurance, for it is in such Societies as Lloyd’s where the best consensus of information regarding the extent and tendencies of particular types of vessels can be obtained. In point of fact, the intervening period has witnessed, in great measure, a realisation of Mr John’s forecast. The advantages of a cellular bottom as regards safety, and for the purpose of ballasting and trimming vessels, also as meeting the greater need for longitudinal strength caused by the enormous growth in the size of vessels, have received that appreciation from shipowners and shipbuilders which is their due. The practice has accordingly spread, till now, it would not be rash to say, quite as many of the ocean-trading steamers being built are fitted with cellular bottoms as are without them.

The adaptation of water ballast to sailing vessels, as well as to steamers, has received consideration at the hands of both Tyne and Clyde builders. Previous to 1877, several small sailing ships were built on the Tyne, in which provision was made for water ballast in tanks entering into the structure of the bottom, but erected over the ordinary plate floors. About 150 tons of water ballast were carried by these vessels, the filling and discharge of the tanks being effected by Downton’s pumps, worked by the crew. The trade in which they were engaged—i.e.—carrying coal from the Tyne to Spanish ports, and back to this country with ore—was one in which the introduction of water ballast proved commercially and otherwise most advantageous. Two years subsequently Messrs A. M‘Millan & Son, Dumbarton, introduced water ballast into one of the largest class of sailing vessels then being built. Unlike previous sailing ships with provision for water ballast, however, the vessel was constructed on the structural cellular bottom principle, having bracket floors and continuous girders, as so generally approved in steamships. Capacity for water ballast, to the extent of over 300 tons was thus provided, the filling and discharge being effected by a special donkey engine, supplied with steam from a large donkey boiler. The boiler also furnished the motive power for cargo winches, off which, by crank gear, the manual labour pumps were also brought into requisition. Facilities for the expeditious management of ballast—the want of which, in sailing vessels, considerably hinders its adoption—were thus, in this case, efficiently provided. Several other sailing ships, built by Messrs A. M‘Millan & Son, and by other shipbuilding firms on the Clyde, have been fitted with this system, and the result of experience with these vessels in actual service, thoroughly encourages its more general adoption.