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20 ' MARINE REVIEW. [December 7, ELECTRIC MOTORS ON SHIPBOARD. NAVY BUREAU OF ENGINEERING STILL DECIDEDLY OPPOSED TO THEM--HOWEVER . GOOD ELSEWHERE, THEY ARE NOT YET ADAPTED TO DRIVING AUXILIARIES ON SHIPS---CLAIMS ON SCORE OF ECONOMY NOT TENABLE. REAR-ADM RAL MELVILLE, U. S. N.* For some time past--in fact, ever since the successful use of electric motors for general power purposes on shore--the bureau of steam engi- neering of the United States navy has been carefully investigating their adaptability to the driving of the numerous auxiliary engines on board ship, and, in view of the conclusion that the electric drive of the auxil- iaries would not, under existing conditions, be so satisfactory and economical, on the whole, as the steam drive, believes it would be of in- terest to state the reasons for this conclusion. This is the more ap- propriate because in some quarters the fact that electric motors are ex- tensively used on shore has lead to the belief that they would be equally successful on board ship. The bureau has planned to use electric motors exclusively in its new plant at the Brooklyn navy yard, and it will be. readily appreciated, therefore, that their non-use on board ship is for very good reasons. The advantages claimed for electric motors over small steam engines on board ship may be classed as greater ease of operation, avoidance of heat, which accompanies the use of steam pipes in living places, and much greater economy. Against these, however, are to 'be put the much greater weight of the necessary electric outfit,. the greater delicacy of the type of electric motors ordinarily used, the lack of ready adaptability to the various conditions of service, a general denial of the claims for economy as ordinarily presented,:and the increase in the amount of space required below the protective deck for the in- stallation of the necessary dynamo rooms, this space being necessarily taken from coal bunkers. _ On board ship, where excess of weight is so carefully guarded against, it would certainly be very unwise to adopt a change of motive power involving great increase in weight, unless the advantages gained are very material. It must always be remembered that, speaking gener- ally, on board ship the use of an electric motor involves a total weight for the motive power at least three times that of the motor itself, because there is always the generator and its driving engine, besides the motors supplied by them; or, in other words, the electric drive of an auxiliary will weigh at least three times as much as the steam drive, assuming the motor to weigh no more than the engine it displaces, although usually it does weigh more. The answer which would 'be made to this is, of course, very familiar to anybody who has studied the problem, viz., that the auxiliaries are not all in use at one time, and that therefore the generator capacity required is considerably less than the total motor capacity. This is another case where a statement which may be true elsewhere is not true for the circumstances on board ship. Our naval machinery has to be designed so that in time of action everything can be ready for use, and, as a matter of fact, a very little study of the ques- tion will show that it not only may but almost certainly would happen that every auxiliary on the ship, except the capstan engine and some of the boat winches, would be used simultaneously. Therefore this state- ment with regard to the generator capacity does not hold on board ship. Another statement to which very emphatic objection must be entered is in respect to the enormous gain in economy claimed for the electric drive of the auxiliaries, which is obtained by taking the highest figure for the efficiency of the generator and motor and also the most econom- ical steam engine, and 'by comparing these results with the uneconomical form of steam cylinders which, for very good reasons, have until recently ordinarily been used with the steam-driven auxiliaries. If the electric generator was of relatively large size and the motors worked always at their most economical speed and load there might be some justification for this claim; but, as a matter of fact, the very circumstances under which the auxiliaries on board ship are worked require a very wide range of speed and power, and I believe that electric experts admit that electric motors as at present designed when run under these condi- tions are by no means economical, so that, without considering the economy of the engine driving the electric generator, the economy of motor-driven auxiliaries at speeds differing materially from the most economical would be widely different from those which are set forth by the advocates of their universal use on board ship. The natural result of the foregoing is that, with the widely varying speeds of the auxiliary machinery, there is required at the generator the development of an almost constant power which is very near the maximum, and which depends only upon the number of auxiliaries in use. I wish to emphasize the point that the objection to using electric motors for driving the auxiliaries on board ship is not an objection to the use of electric motors per se, but to installing them in a jlocation for which they are not adapted and where their good features. can not be utilized. What has led to the wide use of electric motors on shore is not only the absence of heat, cleanliness, and ease of installation and operation, but above all the simplicity of the transmission of power from a central station to a distance. Now the great majority of the auxiliaries on board ship are so near the boilers that less piping is involved in a direct steam drive than in an electric drive from dynamos necessarily at some distance from the boilers. The ease of transmitting power to a distance over a wire, as compared with great lengths of steam piping, gives the electric drive a very attractive side, even for distances no greater than the maximum ones on board ship, so that we should naturally expect to find electrically driven capstans and steering engines. These two auxiliaries are not under this bureau, but are the ones requiring long and objectionable steam pipes through the living spaces. Here, however, another point has been made by some who are very anxious to use motors elsewhere, viz., that for the service in these cases motors are not sufficiently reliable. Naturally a system involving four parts, each liable to break down, is more delicate than one involving but two of these parts. With a steam drive there are the boilers and * From the annual report of the Engineer-in-chief, United States Navy. the steam engine driving the auxiliaries. In the electric drive we have the boilers, the steam engines, and also the electric generators and mo- tors. It is merely a detail whether the steam engines operate the auxil- iaries directly or whether a smaller number of them, having a greater power in each engine, operate electric dynamos. Personally I should think, however, that if motors are considered sufficiently reliable to drive feed pumps and air pumps on shipboard, for which they are not well adapted, they would be reliable for these other two cases noted, which they fit so well otherwise. The absurdity of an electric drive of auxiliary machinery on board ship situated closer to the main engines than the engines driving the dynamos becomes all the more apparent when contrasted with the steam drive for auxiliaries situated in the very extreme ends of the ship. The fact is that within what are ordinarily called the "machinery compartments of the ship" the leading of the necessary steam and exhaust pipes for auxiliaries does not interfere with anybody's comfort nor does it raise the temperature unduly, and the distances are so short as to make the lead of piping very easy. Steam auxiliaries answer admirably the demands which come upon them at all speeds within their capacity, and the only possible objection which can be urged against them is that the simple forms usually employed for reliability are not so economical as the more elaborate ones which can be used elsewhere. They are far superior to electric motors on the score of adaptation to the service to, be performed, and also far better for naval use on the score of weight. On the score of economy, we have shown above that the claims ordinarily made for the electric drive are not ten- able, except under special conditions, and it is further to be said for the steam-driven auxiliaries that at the times when economy is of the greatest importance when making long sea trips, only a small part of the total auxiliary capacity is used, so that even if the saving by the use of electricity was what is claimed by the most enthusiastic elec- trical agents the aggregate amount of fuel saved would be compara- tively insignificant and considerably less than the reduction in bunker capacity necessarily incident in a ship of a given size to the use of the electric drive. It must also be noted that all the published statements of the superior economy of electrically operated auxiliaries are based on steam auxiliaries where every steam cylinder was of the least economical kind, and where, for good reasons, well-known measures of economy had not been installed. An inspection of the bureau's recent designs will show that 'by the use of compound engines as motors, feed heaters for the exhaust, the use of the exhaust steam from the auxiliaries in the re- ceivers of the main engines, and other economical devices, the expendi- ture of steam in the auxiliaries is brought much below that of the old simple engines, and indeed below that of the electric drive except under very favorable conditions, while avoiding the increased complication and weight which necessarily accompany electrically driven auxiliaries on board ship. I may be permitted to call attention in this connection to the fact that those designers abroad who have the most extended experience are working on this problem of the economy of auxiliaries along the same lines that the bureau has been following. Although the statement is very often made that the electric drive of the auxiliaries is being rap- idly adopted in all foreign navies, this is far from accurate. It is being tried on some ships in some navies, but is as yet entirely in the experi- mental stage. These experiments have been carried quite as far in our navy as in any other. I think I may be pardoned for saying that those who are most in- sistent on the electric drive are not at all conversant with the condi- tions obtaining on board ship, while those of us who have spent a life- time in the care and design of naval machinery may fairly claim that we know something about what is needed. It is perfectly safe to say that when electric machinery can be used more advantageously than steam for driving ships' auxiliaries the change will be made very prompt- ly. Knowing, as they do, that as at present designed electric machinery, however good elsewhere, is not yet adapted to driving the auxiliaries on board ship, the bureau chiefs would be incompetent if they yielded to the craze for new things and made a change which would result in increase of weight and complication, lack of economy, dissatisfaction, and the de- creased efficiency of the fleet. In this connection I desire to submit the following facts and calculations: On the battleship Alabama the space required for electric motors, where used, is approximately the same as that required for steam engines to do the same work. The space required for the wiring, etc., is less than that necessary for steam piping, had that been used. The space required for the generating sets is 10,140 cubic feet. The capacity of these generating sets is 256 kilowatts total. If all the auxiliary ma- chinery on board this ship were operated by electricity, and if the space required for the electric generators were increased in the ratio of the increase of necessary capacity in the generating room, the space that would be required in the generating rooms would be 50,700 cubic feet for a capacity of 1,280 kilowatts. Consequent upon the extension of the use of electricity would be an increase in the total weight of the ma- chinery equal to from 150 to 250 tons as a minimum. This loss in weight is as much as the gain following the use of water tube boilers. The increased space occupied by the larger generating rooms would accommodate 900 tons of coal, or 8,600 horse power could be added to the power of the propelling engines, giving the ship in the first instance 45 per cent greater coal endurance, or in the second instance 1.5 knots increase in speed. The figures as to the space required for the installa- tion of larger generating sets are undoubtedly excessive, but they are based upon the present practice. It seems to me that at the best we would at present have to pay an excessive price for electricity. This weight and space required would be very much less if the. size of the electric generating units could be largely increased without loss to the efficiency of the ship. At present, however, it 1s necessary for the effi- cient operation of the turret-turning machinery and of the ammunition hoists that small units be used, for these purposes at least. Probably when the designers of electrical machinery for naval use give as much attention to the development of designs to suit naval conditions as they have already done in commercial work this necessity will be overcome. I consider that the turbine engine has a distinct field as \an electric