Chapter 2

It is difficult to compile comparative tables showing the relative expenses for running steam launches, electric launches with secondary batteries, and electric launches with primary zinc batteries; but I have roughly calculated that, for a launch having accommodation for a definite number of passengers, the total costs are as 1, 2.5, and 12 respectively, steam being lowest and zinc batteries highest.

The accumulators are, in this case, charged by a small high pressure steam engine, and a very large margin for depreciation and interest on plant is added. The launch taken for this comparison must run during 2,000 hours in the year, and be principally employed in a regular passenger service, police and harbor duties, postal service on the lakes and rivers of foreign countries, and the like.

The subject of secondary batteries has been so ably treated by Professor Silvanus Thompson and Dr. Oliver Lodge, in this room, that I should vainly attempt to give you a more complete idea of their nature. The improvements which are being made from time to time mostly concern mechanical details, and although important, a description will scarcely prove interesting.

A complete Faure-Sellon-Volckmar cell, such as is used in the existing electric launches, is here on the table; this box weighs, when ready for use, 56 lb.; and it stores energy equal to one horse power for one hour=1,980,000 foot pounds, or about one horse power per minute for each pound weight of material. It is not advantageous to withdraw the whole amount of energy put in; although its charging capacity is as much as 370 ampere hours, we do not use more than 80 per cent., or 300 ampere hours; hence, if we discharge these accumulators at the rate of 40 amperes, we obtain an almost constant current for 7½ hours: one cell gives an E.M.F. of two volts. In order to have a constant power of one horse for 7½ hours, at the rate of 40 amperes discharge, we must have more than nine cells per electrical horsepower; and 47 such cells will supply five electrical horse power for the time stated, and these 47 cells will weigh 2,633 lb.

We could employ half the number of cells by using them at the rate of 80 amperes, but then they will supply the power for less than half the time. The fact, however, that the cells will give so high a rate of discharge for a few hours is, in itself, important, since we are enabled to apply great power if desirable; the 47 cells above referred to can be made to give 10 or 12 electrical horse power for over two hours, and thus propel the boat at a very high speed, provided that the motor is adapted to utilize such powerful currents.

The above mentioned weight of battery power--viz., 2,632 lb., to which has to be added the weight of the motor and the various fittings--represents, in the case of a steam launch, the weight of coals, steam boiler, engine, and fittings. The electro motor capable of giving four horse power on the screw shaft need not weigh 400 lb. if economically designed; this added to the weight of the accumulators, and allowing a margin for switches and leads, brings the whole apparatus up to about 28 cwt.

An equally powerful launch engine and boiler, together with a maximum stowage of fuel, will weigh about the same. There is, however, this disadvantage about the steam power, that it occupies the most valuable part of the vessel, taking away some eight or nine feet of the widest and most convenient part, and in a launch of twenty-four feet length, requiring such a power as we have been discussing, this is actually one-third of the total length of the vessel, and one-half of the passenger accommodation; therefore, I may safely assert that an electric launch will carry about twice as many people as a steam launch of similar dimensions.

The diagram on the wall represents sections of an electric launch built by Messrs. Yarrow and Company, and fitted up by the Electrical Power Storage Company, for the recent Electrical Exhibition in Vienna. She has made a great number of successful voyages on the River Danube during the autumn. Her hull is of steel, 40 feet long and 6 feet beam, and there are seats to accommodate forty adults comfortably. Her accumulators are stowed away under the floor, so is the motor, but owing to the lines of the boat the floor just above the motor is raised a few inches. This motor is a Siemens D2 machine, capable of working up to seven horse power with eighty accumulators.

In speaking of the horse power of an electro motor, I always mean the actual power developed in the shaft, and not the electrical horse power; this, therefore, should not be compared to the indicated horse power of a steam engine.

I am indebted to Messrs. Yarrow for the principal dimensions and other particulars of a high pressure launch engine and boiler, such as would be suitable for this boat. From these dimensions I prepared a second diagram representing the steam power, and when placed in position it will show at a glance how much space this apparatus will occupy. The total length lost in this way amounts to 12 feet, leaving for testing capacity only 15 feet, while that of the electric launch is 27 feet on each side of the boat; thus the accommodation is as fifteen to twenty-seven, or as twenty-two passengers to forty, in favor of the electric launch.

Comparing the relative weights of the steam power and the electric power for this launch, we find that they are nearly equal--each approaches 50 cwt; but in the case of the steam launch we include 10 cwt. of coals, which can be stowed into the bunkers, and which allow fifteen hours continuous steaming, whereas the electric energy stored up will only give us seven and a half hours with perfect safety.

I have here allowed 8 lb. of coal per indicated horse power per hour, and 10 horse power giving off 7 mechanical horse power on the screw shaft; this is an example of an average launch engine. There are launch engines in existence which do not consume one-half that amount of fuel, but these are so few, so rare, and so expensive, that I have neglected them in this account.

Not many years ago, a steam launch carrying a seven hours supply of fuel was considered marvelous.

Our present accumulaton supplies 33,000 foot pounds of work per pound of lead, but theoretically one pound of lead manifests an energy equal to 360,000 foot pounds in the separation from its oxide; and in the case of iron, Prof. Osborne Reynolds told us in this place, the energy evolved by its oxidation is equivalent to 1,900,000 foot pounds per pound of metal. How nearly these limits may be approached will he the problem of the chemist; to prophesy is dangerous, while science and its applications are advancing at this rapid rate.

Theoretically, then, with our weight of fully oxidized lead we should be able to travel for 82 hours; with the same weight of iron for 430 hours, or 18 days and nights continually, at the rate of 8 miles per hour, with one change. Of course, these feats are quite impossible. We might as well dream of getting 5 horse power out of a steam engine for one pound of coal per hour.

While the chemist is busy with his researches for substances and combinations which will yield great power with small quantities of material, the engineer assiduously endeavors to reconvert the chemical or electrical energy into mechanical work suitable to the various needs.

To get the maximum amount of work with a minimum amount of weight, and least dimensions combined with the necessary strength is the province of the mechanical engineer--it is a grand and interesting study; it involves many factors; it is not, as in the steam engine and hydraulic machine, a matter of pressures, tension and compression, centrifugal and static forces, but it comprises a still larger number of factors, all bearing a definite relation to each other.

With dynamo machines the aim has been to obtain as nearly as possible as much electrical energy out of the machine as has been put in by the prime mover, irrespective of the quantity of material employed in its construction. Dr. J. Hopkinson has not only improved upon the Edison dynamo, and obtained 94 per cent. of the power applied in the form of electrical energy, but he got 50 horse power out of the same quantity of iron and copper where Edison could only get 20 horsepower--and, though the efficiency of this generator is perfect, it could not be called an efficient motor, suitable for locomotion by land or water, because it is still too heavy. An efficient motor for locomotion purposes must not only give out in mechanical work as nearly as possible as much as the electrical energy put in, but it must be of small weight, because it has to propel itself along with the vehicle, and every pound weight of the motor represents so many foot pounds of energy used in its own propulsion; thus, if a motor weighed 660 pounds, and were traveling at the rate of 50 feet per minute, against gravitation, it would expend 33,000 foot pounds per minute in moving itself, and although this machine may give 2 horse power, with an efficiency of 90 per cent. it would, in the case of a boat or a tram-car, be termed a wasteful machine. Here we have an all-important factor which can be neglected, to a certain extent, in the dynamo as a generator, although from an economical point of view excessive weight in the dynamo must also be carefully avoided.

The proper test for an electro-motor, therefore, is not merely its efficiency, or the quotient of the mechanical power given out, divided by the electrical energy put in, but also the number of feet it could raise its own weight in a given space of time, with a given current, or, in other words, the number of foot pounds of work each pound weight of the motor would give out.

The Siemens D2 machine, as used in the launch shown in the diagram on the wall, is one of the lightest and best motors, it gives 7 horse power on the shaft, with an expenditure of 9 electrical horsepower, and it weighs 658 lb.; its efficiency, therefore, 7/5 or nearly 78 per cent.; but its "coefficient" as an engine of locomotion is 351--that is to say, each pound weight of the motor will yield 351 foot pounds on the shaft. We could get even more than 7 horse power out of this machine, by either running it at an excessive speed, or by using excessive currents; in both cases, however, we should shorten the life of the apparatus.

An electro-motor consists, generally, of two or more electro-magnets so arranged that they continually attract each other, and thereby convey power. As already stated, there are numerous factors, all bearing a certain relationship to each other, and particular rules which hold good in one type of machine will not always answer in another, but the general laws of electricity and magnetism must be observed in all cases. With a given energy expressed in watts, we can arrange a quantity of wire and iron to produce a certain quantity of work; the smaller the quantity of material employed, and the larger the return for the energy put in, the greater is the total efficiency of the machine.

Powerful electro-magnets, judiciously arranged, must make powerful motors. The ease with which powerful electro-magnets can be constructed has led many to believe that the power of an electro-motor can be increased almost infinitely, without a corresponding increase of energy spent. The strongest magnet can be produced with an exceedingly small current, if we only wind sufficient wire upon an iron core. An electro-magnet excited by a tiny battery of 10 volts, and, say, one ampere of current, may be able to hold a tremendous weight in suspension, although the energy consumed amounts to only 10 watts, or less than 1/75 of a horse power, but the suspended weight produces no mechanical work. Mechanical work would only be done if we discontinued the flow of the current, in which case the said weight would drop; if the distance is sufficiently small, the magnet could, by the application of the current from the battery, raise the weight again, and if that operation is repeated many times in a minute, then we could determine the mechanical work performed. Assuming that the weight raised is 1,000 lb., and that we could make and break the current two hundred times a minute, then the work done by the falling mass could, under no circumstances, equal 1/75 of a horse-power, or 440 foot-pounds; that is, 1,000 lb. lifted 2.27 feet high in a minute, or about one-eighth of an inch for each operation: hence the mere statical pull, or power of the magnet, does in no way tend to increase the energy furnished by the battery or generator, for the instant we wish to do work we must have motion--work being the product of mass and distance.

Large sums of money have virtually been thrown away in the endeavor to produce energy, and there are intelligent persons who to this day imagine that, by indefinitely increasing the strength of a magnet, more power may be got out of it than is put in.

Large field-magnets are advantageous, and the tendency in the manufacture of dynamo machines has been to increase the mass of iron, because with long and heavy cores and pole pieces there is a steady magnetism insured, and therefore a steady current, since large masses of iron take a long time to magnetize and demagnetize; thus very slight irregularites in the speed of an armature are not so easily perceived. In the case of electro-motors these conditions are changed. In the first place, we assume that the current put through the coils of the magnets is continuous; and secondly, we can count upon the momentum of the armature, as well as the momentum of the driven object, to assist us over slight irregularities. With electric launches we are bound to employ a battery current, and battery currents are perfectly continuous--there are no sudden changes; it is consequently a question as to how small a mass of iron we may employ in our dynamo as a motor without sacrificing efficiency. The intensity of the magnetic field must be got by saturating the iron, and the energy being fixed, this saturation determines the limit of the weight of the iron. Soft wrought iron, divided into the largest possible number of pieces, will serve our purpose best. The question of strength of materials plays also an important part. We cannot reduce the quantity and division to such a point that the rigidity and equilibrium of the whole structure is in any way endangered.

The armature, for instance, must not give way to the centrifugal forces imposed upon it, nor should the field magnets be so flexible as to yield to the statical pull of the magnetic poles. The compass of this paper does not permit of a detailed discussion of the essential points to be observed in the construction of electro-motors; a reference to the main points, may, however, be useful. The designer has, first of all, to determine the most effective positions of the purely electrical and magnetic parts; secondly, compactness and simplicity in details; thirdly, easy access to such parts as are subject to wear and adjustment; and, fourthly, the cost of materials and labor. The internal resistance of the motor should be proportioned to the resistances of the generator and the conductors leading from the generator to the receiver.

The insulation resistances must be as high as possible; the insulation can never be too good. The motor should he made to run at that speed at which it gives the greatest power with a high efficiency, without heating to a degree which would damage the insulating material.

Before fixing a motor in its final position, it should also be tested for power with a dynamometer, and for this purpose a Prony brake answers very well.

An ammeter inserted in the circuit will show at a glance what current is passing at any particular speed, and voltmeter readings are taken at the terminals of the machine, when the same is standing still as well as when the armature is running, because the E.M.F. indicated when the armature is at rest alone determines the commercial efficiency of the motor, whereas the E M.F. developed during motion varies with the speed until it nearly reaches the E.M.F. in the leads; at that point the theoretical efficiency will be highest.

Calculations are greatly facilitated, and the value of tests can be ascertained quickly, if the constant of the brake is ascertained; then it will be simply necessary to multiply the number of revolutions and the weight at the end of the lever by such a constant, and the product gives the horse power, because, with a given Prony brake, the only variable quantities are the weight and the speed. All the observations, electrical and mechanical, are made simultaneously. The electrical horse power put into the motor is found by the well known formula C x E / 746; this simple multiplication and division becomes very tedious and even laborious if many tests have to be made in quick succession, and to obviate this trouble, and prevent errors, I have constructed a horse power diagram, the principle of which is shown in the diagram (Fig. 1).

Graphic representations are of the greatest value in all comparative tests. Mr. Gisbert Kapp has recently published a useful curve in the _Electrician_, by means of which one can easily compare the power and efficiency at a glance (Fig. 2).

The speeds are plotted as abscissae, and the electrical work absorbed in watts divided by 746 as ordinates; then with a series-wound motor we obtain the curve, EE. The shape of this curve depends on the type of the motor. Variation of speed is obtained by loading the brake with different weights. We begin with an excess of weight which holds the motor fast, and then a maximum current will flow through it without producing any external work. When we remove the brake altogether, the motor will run with a maximum speed, and again produce no external work, but in this case very little current will pass; this maximum speed is om on the diagram. Between these two extremes external work will be done, and there is a speed at which this is a maximum. To find these speeds we load the brake to different weights, and plot the resulting speeds and horse powers as abscissae and ordinates producing the curve, BB. Another curve,

e = B/E

made with an arbitrary scale, gives the commercial efficiency; the speed for a maximum external horse power is o a, and the speed for the highest efficiency is represented by o b. In practice it is not necessary to test a motor to the whole limits of this diagram; it will be sufficient to commence with a speed at which the efficiency becomes appreciable, and to leave off with that speed which renders the desired power.

I have now to draw your attention to a new motor of my own invention, of the weight of 124 lb., which, at 1,550 revolutions, gives 31 amperes and 61.5 volts at terminals. The mechanical horse power is 1.37, and the coefficient 373.

Ohms. Armature resistance 0.4 w. Field-magnet resistance 0.17 w. Insulation resistance 1,500,000 w.

This motor was only completed on the morning before reading the paper; it could not, therefore, be tested as to its various capacities.

We have next to consider the principle of applying the motive power to the propulsion of a launch. The propellers hitherto practically applied in steam navigation are the paddle-wheel and the screw. The experience of modern steam navigation points to the exclusive use and advantage of the screw propeller where great speed of shaft is obtainable, and the electric engine is pre-eminently a high-speed engine, consequently the screw appears to be most suitable to the requirements of electric boats. By simply fixing the propeller to the prolonged motor shaft, we complete the whole system, which, when correctly made, will do its duty in perfect order, with an efficiency approaching theory to a high degree.

Whatever force may be imparted to the water by a propeller, such force can be resolved into two elements, one of which is parallel, and the other in a plane at right angles to the keel. The parallel force alone has the propelling effect; the screw, therefore, should always be so constructed that its surfaces shall be chiefly employed in driving the water in a direction parallel to the keel from stem to stern.

It is evident that a finely pitched screw, running at a high velocity, will supply these conditions best. With that beautiful screw lying on this table, and made by Messrs. Yarrow, 95 per cent. of efficiency has been obtained when running at a speed of over 800 revolutions per minute--that is to say, only 5 per cent was lost in slip.

Reviewing the various points of advantage, it appears that electricity will, in time to come, be largely used for propelling launches, and, perhaps, something more than launches.

In conclusion, quoting Dr. Lardner's remarks on the subject of steam navigation of nearly fifty years ago, he said:

"Some, who, being conversant with the actual conditions of steam engineering as applied to navigation, and aware of various commercial conditions which must affect the problem, were enabled to estimate calmly and dispassionately the difficulties and drawbacks, as well as the disadvantages, of the undertaking, entertained doubts which clouded the brightness of their hopes, and warned the commercial world against the indulgence of too sanguine anticipation of the immediate and unqualified realization of the project. They counseled caution and reserve against an improvident investment of extensive capital in schemes which still be only regarded as experimental, and which might prove its grave. But the voice of remonstrance was drowned amid the enthusiasm excited by the promise of an immediate practical realization of a scheme so grand.

"It cannot," he continues, "be seriously imagined that any one who had been conversant with the past history of steam navigation could entertain the least doubt of the abstract practicability of a steam vessel making the voyage between Bristol and New York. A steam vessel, having as cargo a couple of hundred tons of coals, would, _cæteris paribus_, be as capable of crossing the Atlantic as a vessel transporting the same weight of any other cargo."

Dr. Lardner is generally credited with having asserted that a steam voyage across the Atlantic was "a physical impossibility," but in the work from which I took the liberty of copying his words he denies the charge, and says that what he did affirm was, that long sea voyages could not at that time be maintained with that regularity and certainty which are indispensable to commercial success, by any revenue which could be expected from traffic alone.

The practical results are well known to us. History repeats itself, and the next generation may put on record our week attempts, our doubts and fears of this day. Whether electricity will ever rival steam, remains yet to be proved; we may be on the threshold of great things. The premature enthusiasm has subsided, and we enter upon the road of steady progress.