Twentieth Century Inventions: A Forecast

by George Sutherland

SHIPS.

The "cargo slave" and the "ocean greyhound" are already differentiated by marked characteristics, and in the twentieth century the divergence between the two types of vessels will become much accentuated. The object aimed at by the owners of cargo boats will be to secure the greatest possible economy of working, combined with a moderately good rate of speed, such as may ensure shippers against having to stand out of their capital locked up in the cargo for too long a period. Hence cheap power will become increasingly a desideratum, and the possible applications of natural sources of energy will be keenly scrutinised with a view to turning any feasible plan to advantage. The sailing ship, and the economic and constructive lines upon which it is built and worked, will be carefully overhauled with a view to finding how its deficiencies may be supplemented and its good points turned to account. One result of this renewed attention will be to confirm, for some little time, the movement which showed itself during the past decade of the nineteenth century for an increase of sailing tonnage. Sooner or later, however, it will be recognised that sail power must be largely supplemented, even on the "sailer," if it is to hold its own against steam.

For mails and passengers, on the other hand, steam must more and more decidedly assert its supremacy. Yet the mail-packet of the twentieth century will be very different from packets which have "made the running" towards the close of the nineteenth. She will carry little or no cargo excepting specie, and goods of exceptionally high value in proportion to their weight and bulk. Nearly all her below-deck capacity, indeed, will be filled with machinery and fuel. She will be in other respects more like a floating hotel than the old ideal of a ship, her cellars, so to speak, being crammed with coal and her upper stories fitted luxuriously for sitting and bed rooms and brilliant with the electric light. But in size she will not necessarily be any larger than the nineteenth century type of mail steamer. Indeed the probability is that, on the average, the twentieth century mail-packets will be smaller, being built for speed rather than for magnificence or carrying capacity.

The turbine-engine will be the main factor in working the approaching revolution in mail steamer construction. The special reason for this will consist in the fact that only by its adoption can the conditions mentioned above be fulfilled. With the ordinary reciprocating type of marine steam machinery it would be impossible to place, in a steamer of moderate tonnage, engines of a size suitable to enable it to attain a very high rate of speed, because the strain and vibration of the gigantic steel arms, pulling and pushing the huge cranks to turn the shafting, would knock the hull to pieces in a very short time. For this very reason, in fact, the marine architect and engineer have hitherto urged, with considerable force of argument, that high speed and large tonnage must go concomitantly. Practically, only a big steamer, with the old type of marine-engine, could be a very fast one, and, for ocean traffic at any rate, a smaller vessel must be regarded as out of the running. Very large tonnage being thus made a prime necessity, it followed that the space provided must be utilised, and this need has tended to perpetuate the combination of mail and passenger traffic with cargo carrying.

The first step towards the revolution was taken many years ago when the screw propeller was substituted for the paddle-wheel. The latter means of propulsion caused shock and vibration not only owing to the thrusts of the piston-rod from the steam-engine itself, but also from the impact of the paddles upon the water one after the other. A great increase in the smoothness of running was attained when the screw was invented—a propeller which was entirely sunk in the water and therefore exercised its force, not in shocks, but in gentle constant pressure upon the fluid around it. Such as the windmill is for wind and the turbine water-wheel for water was the screw propeller, although adapted, not as a generator, but as an application of power. Having made the work and stress continuous, the next thing to be accomplished was to effect a similar reform in the engines supplying the power. This is accomplished in the turbine steam-engine by causing the steam to play in strong jets continuously and steadily upon vanes which form virtually a number of small windmills. Thus, while the screw outside of the hull is applying the force continuously, the steam in the inside is driving the shafting with equal evenness and regularity.

The steam turbine does not appear to have by any means reached finality in its form, such questions as the angle of impact which the jet should make with the surface of the vane, and the size of the orifice through which the steam should be ejected, being still debatable points. But on one matter there is hardly any room for doubt, and that is that the best way to secure the benefit of the expansive power of steam is to permit it to escape from a pipe having a long series of orifices and to impinge upon a correspondingly numerous series of vanes, or, perhaps, upon a number of vanes arranged so that each one is long enough to receive the impact of many jets.

Hitherto the steam supply-pipe emitting the jet has been placed outside of the circle of the wheel; but the future form seems likely to be one in which the axis of the wheel is itself the pipe which contains the steam, but which permits it to escape outwards to the circumference of the wheel. The latter is, in this form of turbine, made in the shape of a paddle-wheel of very small circumference but considerable length, the paddles being set at such an inclination as to obtain the greatest possible rotative impulse from the outward-rushing steam. The pipe must be turned true at intervals to enable it to carry a number of diminutive wheels upon which these long vanes are mounted, and a very strong connection must be made between these wheels and the shaft of the screw. Inasmuch as a high speed of rotation is to be maintained, the pitch of the screw in the water is set so as to offer but slight opposition to the water at each turn. The immense speed attained is thus due, not to the actual power with which the water is struck by the screw at each revolution, but to the extraordinary rapidity with which the shaft rotates.

The twin screw, with which the best and safest of modern steam-ships are all fitted, will soon develop into what may be called "the twin stern". Each screw requires a separate set of engines and the main object of the duplication is to lessen the risk of the vessel being left helpless in case of accident to one or other. The advisability of placing each engine and shafting in a separate water-tight compartment has therefore been seen. At this point there presents itself for consideration the advisability of separating the two screws by as wide a distance as may be convenient and placing the rudder between the two. Practically, therefore, it will be found best to build out a steel framework from each side of the stern for holding the bearings of each screw in connection with the twin water-tight compartments holding the shafting; and thus will be evolved what will practically represent a twin, or double, stern.

In the case of the turbine steamer several of the forms of screw which were first proposed when that type of propeller was invented will again come up for examination, notably the Archimedean screw, wound round a fairly long piece of shafting. The larger the circular area of this screw is the less will be the risk of "smashing" the water, or of losing hold of it entirely in rough weather. With twin screws of the large Archimedean type the propelling apparatus of a turbine steamer will—if the screws are left open—be objected to on the ground of liability to foul or to get broken in crowded fairways. Hence will arise a demand for accommodation for each screw in a tube forming part of the lower hull itself and open at the side for the taking in of water, while the stern part is equally free. In this way there is evolved a kind of compromise between the two principles of marine propulsion, by a screw and by a jet of water thrown to sternward. The water-jet is already very successfully employed for the propulsion of steam lifeboats in which, owing to the danger of fouling the life-saving and other tackle, an open screw is objectionable.

The final extermination of the sailing ship is popularly expected as one of the first developments of the twentieth century in maritime traffic. Steam, which for oversea trade made its entrance cautiously in the shape of a mere auxiliary to sail power, had taken up a much more self-assertive position long before the close of the nineteenth century, and has driven its former ally almost out of the field in large departments of the shipping industry. Yet a curious and interesting counter movement is now taking place on the Pacific Coast of America, as well as among the South Sea Islands and in several other places where coal is exceptionally dear. Trading schooners and barques used in these localities are often fitted with petroleum oil engines, which enable them to continue their voyages during calm or adverse weather. For the owners of the smaller grade of craft it was a material point in recommendation of this movement that, having no boiler or other parts liable to explode and wreck the vessel, an oil engine may be worked without the attendance of a certificated engineer. As soon as this legal question was settled a considerable impetus was given to the extension of the auxiliary principle for sailing ships. The shorter duration of the average voyage made by the sail-and-oil power vessels had the effect of enabling shippers to realise upon the goods carried more speedily than would have been possible under the old system of sail-power alone.