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barges of the same dimensions and ton- nage, which are now being completed. These craft are additionally strengthened transversely by concrete beams, which extend straight across the holds. The external shell is divided into panels, and when a rent is made in the fabric, it is necessary only to lay bare the iron rein- forcement at the point of injury, repair the damaged sections of metal armoring and network, and apply the coating of cement. In this manner the most exten- sive injuries can be easily repaired in the course of a few hours. The system moreover is more hygienic than either wood or iron, and can easily be main- tained in a perfectly clean condition, the holds being flushed out with a hose. Signor Gabellini is advocating the manufacture of armor plates upon this principle. The system is fundamentally the same as adopted in torpedo boats, but is considerably strengthened. The plate is built up to the requisite thickness of superimposed layers of the armoring, with intervening layers of cement, and so made as to form a perfectly homo- geneous plate. In this arrangement the -iron rods are disposed at right angles to one another in each layer, to secure the maximum effect of resistance and strength. The number of layers of rein- forcement can be varied as desired. From the experiments the inventor has made he has determined that it is pos- sible to secure the same degree of re- sistance to projectiles as a given steel plate with from 33 to 50 per cent less material. The advantage of such a plate, he points out, in addition to its high de- gree of resistance to penetration, is the facility with which it can be repaired. Concrete boats are not altogether a novelty in the United States. An engin- -eering firm in Missouri has been engaged 'for some time in building small concrete power-propelled boats for river use. GAS-DRIVEN BATTLESHIPS. Discussing. the recent experiments with gas engines as the means of pro- pelling. battleships, conducted by the British naval department, fitting out the old ship Rattler with 50-H. P. engines, and a later report, that the admiralty had ordered a 19,- 500-ton battleship of this type, Dr. Charles E. Lucke, professor of me- chanical engineering in Columbia Un- iversity, said that the upholders of the gas engine were too forward in their claims. "It is my opinion that Nixon is too optiniistic,' said Dr. Lucke. "There is no doubt that the combina- tion of gas producer and engine will drive vessels more economically than steam, and that labor conditions in the ships will be improved by the "TAE. Marine Review adoption of this kind of power. But we have not the producer or the en- gine as yet. You cannot go in the market today and buy a gas engine that will drive a large ship. There are plenty of designers that will promise to build one, but engineering experience has proven that it is a long trip from designer to successful installation. "The adaptability of stationary gas engines to the propulsion of battle- ships and liners is entirely possible, but it will not come in many years; it will not be tomorrow nor the next day. The experimental stage may be- gin actively at once--the reduction to engineering practice is a development of some time: should put it at from 5 to 10 years; approximately in 10 years. we will have a ship that might be considered as standard. "The British navy spends much more on experiments than that of the United States, and the reports of the adoption of the gas engine do not mean anything final, but rather that it considers it a profitable field of in- vestigation. I could not advise the United States naval: authorities to even begin experiments; it is too soon to begin now. The engine and pro- ducer should be bettered by private study and trials on the part of those that are interested. "There is one serious drawback to the installation of the gas engine and producer as it is at present in ocean traffic, and especially in the tramp freighters, with their irregular ports of call, and that is the problem of coal supply. The gas producer, as we know it now, is by no means so flexible in its use of coal as the steam boiler, although Mr. Nixon claims that he can burn a variety of fuels. "Tt has often been said that the gas producer can handle any kind of coal, and so it can, but not commer- cially. The automobile is eminently successful as a vehicle, but in does not compete with the railroads as a carrier of freight traffic. A thing of this kind that cannot be done com- mercially is not successfully applied. Any gas producer might burn any kind of coal, but there would be so much trouble that it would be im- practicable froma _ business standpoint, I think that Mr. Nixon is too opti- mistic in claiming the latitude of fuels which he mentions. "The engine does not offer so many difficulties as the producer, though there is no engine now built that could be thought nearly ready for application to the problem of battleship propulsion. There is no 55 vertical engine large enough; some designers believe that they could build one right away, but the fact remains that none has been made. It means time, money, and thought ex- pended in years of experiment. I say again that the ships driven by gas engines will come, but I wish to correct the notion that they have arrived. "In the matter of the saving of coal, the proportionate consumption, compared to steam, varies as the size of the gas engine. The largest gas engine at present is ome of 5,500 horsepower in the. power house of the San Francisco Gas & Electric Co., and we may base our figures on that. Fhe saving in the larger sizes, gay Of "over ::'10,000~ Ee Pa wowed - pe 20 per cent, to put it at more would be too optimistic; in smaller installa- tions, of units under 1,000 horsepower, it might be from 75 per cent to 90 per cent. As you see this consider- ation grows less and less in import- ance in the larger engines, and those required for a_ battleship would be of the largest. "The 'only investigations that have been conducted have been by the United States Geological Survey, in their experiments towards the con- serving of the fuels of the country. They made investigations in the pos- sible use of low grade coals--the brown coals and lignites--with a view to finding out the difference in the consumption of the two types of en- gine. The comparison showed the gas engine to be the most economi- cal, but the fact remains that these figures are often misinterpreted, and false conclusions are drawn, for it is certain that the larger plants will not make so good a _ showing. "Again, the first costs of the gas installation will always be greater than the steam, and this makes com- petition far less favorable until the gas engine has reached at least a more stable foundation. "Tt is in the problem of labor that the gas engines as applied to ships will bring about the greatest saving and better conditions. The terrible heat and overwork of the stoking will be eliminated, and the whole ship will be more comfortable. "T look for the first application of the gas engine to canal and river traffic, where the power required is less and the demand on the flexibility is not so great as in the trans-oceanic liners. When this has been success- fully tried and proved, then we may turn to the battleships and ocean lin- ers, but not before."