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318 operation which, in itself somewhat difficult, becomes impossible if a lib- eral supply of compressed air be not available. To keep up a supply of compressed air for manoeuvring the vessels in the locks and channels of a canal involves the upkeep of a very expensive and inefficient air-compress- ing plant, and the dispensing with this auxiliary is a very important feature of the system. It is also advantage- ous to have two units, each capable of driving the ship, so that in the event of an interruption to the run- ning of either the vessel is still under control. Functions of Electrical Equipment The functions performed by the electric equipment may be recapitu- . lated:-- 1. It\ adapts the speed of the en- gine to the speed of the propeller. 2. It combines the power of sep- arate engines and applies the whole to a single propeller, with perfect freedom to use either or both power units. 3. It provides a simple and easy reversal of the propeller, while leav- ing the engines running in one di- rection at constant speed. 4. It also provides ready means of distant control should this be re- quired. It will be seen that the use of me- chanical gearing could perform the first, and the first only, of these func- tions, and for this reason it is antic- ipated that, compared with a mechan- ically-geared or direct-connected Die- sel engine equipment, the electrical equipment will offer very material advantage in the operation of the vessel in the special circumstances under which it is placed. The writers have endeavored to show how important, and, indeed, even indispensable for reliability and efficiency, the use of electric trans- mission may be in the propulsion of so relatively simple a type as this Canadian barge where it is decided to adopt the Diesel engine. This should help to dispose of the too prevalent idea that the natural scope for elec- trical propulsion is in war-ships or other highly specialized vessels, in which electricity might provide means for adjusting economically the power generated to the very conflicting power requirements, say, under peace and war conditions. Undoubtedly a battleship or battle-cruiser does offer the very best scope for the electric drive, but only because that class of vessel presents_on a large scale the same problems in propulsion which are found in almost all other vessels-- viz., how to adjust efficiently and eco- THE MARINE REVIEW nomically the power available to the power required at any given time, not necessarily always from the point of view of propulsion alone. From the analysis of the voyage logs of an ordinary tramp steamer, the second writer has shown (see Electrician, June 10, 1910,) how im- portant towards efficiency of propul- sion might be the introduction of electric transmission, with the added economy of a modern high-speed re- action turbine as the power-generator in place of the usual triple-expansion engine, and, of course, in this case such possibilities of economy are confirmed by the results since ob- tained with mechanical gearing intro- duced for the same purpose. An ad- vantage, however, lies with the elec- trical arrangement, in that it permits a much wider range and variation of revolutions between the propeller and the turbine, permitting also a more advantageous subdivision of the gen- erating plant into units of different sizes, and finally eliminating the ne- cessity for reverse in the turbine and simplifying the control. In the United States, Mr. Emmett, of the General Electric Company, has also shown the suitability of electric propulsion for a deep-sea collier of great size and 7;000 h. p, for which the equipment has already been com- pleted and tested with the most bril- liant results. From such a vessel to a large passenger liner such as the Celtic is a mere step, and in such ves- sels also the possibilities of economy and all-round efficiency are most marked. General Efficiency In such matters it is much too com- mon to pronounce judgment for or against without adequate analysis of the problems which are as numerous and varied as the vessels which come up for consideration. In this connec- tion, trial-trip data, however valuable for comparative purposes, cannot be used as a guide, because what we are concerned with is maximum efficiency in working conditions; not propelling efficiency alone, but the innumerable phases of the working of a ship, of which propulsion is, perhaps, the most important, all of which have a bear- ing on the general efficiency of its operation. Experience: in developing a comparatively simple type, such as this Canadian canal vessel, shows that it is frequently quite impossible to convey to the builder any adequate conception of how such a vessel is handled, and has to be handled, to get maximum efficiency out of it in the short six months' season. What Lord Kelvin used to call the "bias September, 1913 of preconceived notions" is apt to prevent a detached view on the part of a builder, especially when a de- cided departure from established prac- tice and precedent is called for. For example, the idea that special. scant- ling provisions forward should be fitted to any type of vessel to enable it to "butt" stone walls: and quays with impunity seems to many builders very unreasonable, though the same builders might not hesitate to fit special bow stiffening against ice. Scope in Marine Propulsion It is for this same reason that one is not surprised to meet with consid- erable scepticism in regard to the scope for electricity in marine propul- sion. To the majority of sea-going engineers the idea of a transmission feature between the _ driving-engine and the propeller is simply anathema. To prevent such an introduction an infinity of pains will be devoted to experimenting with high-speed _ pro- pellers and low-speed turbines - and oil-engines with an all-round lowering of total efficiency and an increase in| complication actually in excess of that which it is desired to avoid. There are not 10 per cent of the merchant vessels now afloat which. would not be most efficiently propelled by screws designed to turn at _ revolu- tions not exceeding 80 per minute, and for real progress towards maxi- mum efficiency in marine propulsion one should at all costs retain the sim- plest form of propeller, the efficiency of which permits of no dispute, and from that basis arrive through the various methods of transmission now available at an arrangement of ma- chinery best suited to each -individual case. At the start such a. scheme of powering a vessel would work a hard- ship on the builders of standard ma- rine machinery; but it should be. un- derstood that, in advocating the use of transmission gearing, one does so to enable the newer forms of power generators to be utilized. Nothing is more likely to retard the introduction of the internal-combus- tion engine in marine work than the mistaken attempt to treat it as a per- fect substitute for the triple-expansion engine which it is intended to dis- place. It is at this point that elec- tricity acts as a safeguard in a way that no other system of transmission can approach. There are, of course, problems of Propulsion, the analysis. of which shows that approximately equal re- sults may be obtained whichever form of transmission gearing--electric, hy- draulic, or mechanical--is adopted. In such cases the decision will, no doubt,