It may not be generally known that an electric launch was tried for experimental purposes, on a lake at Pentlegaer, near Swansea. Mr. Robert Hunt, in the discussion of his paper on electromagnetism before the Institution of Civil Engineers in 1858, mentioned that he carried on an extended series of experiments at Falmouth, and at the instigation of Benkhausen, Russian Consul-General, he communicated with Jacobi upon the subject. In the year 1848, at a meeting of the British Association at Swansea, Mr. Hunt was applied to, by some gentlemen connected with the copper trade of that part, to make some experiments on the electrical propulsion of vessels; they stated, that although electricity might cost thirty times as much as the power obtained from coal it would, nevertheless, be sufficiently economical to induce its employment for the auxiliary screw ships employed in the copper trade with South America.
The boat at Swansea was partly made under Mr. (now Sir William) Grove's directions, and the engine was worked on the principle of the old toys of Ritchie, which consisted of six radiating poles projecting from a spindle, and rotating between a large electro-magnet. Three persons traveled in Hunt's boat, at the rate of three miles per hour. Eight large Grove's cells were employed, but the expense put it out of question as a practical application.
Had the Gramme or Siemens machine existed at that time, no doubt the subject would have been further advanced, for it was not merely the cost of the battery which stood in the way, but the inefficient motor, which returned only a small fraction of the power furnished by the zinc.
Professor Silvanus Thompson informs us that an electric boat was constructed by Mr. G. E. Dering, in the year 1856, at Messrs. Searle's yard, on the River Thames; it was worked by a motor in which rotation was effected by magnets arranged within coils, like galvanometer needles, and acted on successively by currents from a battery.
From a recent number of the Annales de l'Electricite, we learn that Count de Moulins experimented on the lake in the Bois de Boulogne, in the year 1866, with an iron flat-bottomed boat, carrying twelve persons. Twenty Bunsen cells furnished the current to a motor on Froment's principle turning a pair of paddle wheels.
In all these reports there is a lack of data. We are interested to know what power the motors developed, the time and speed, as well as dimensions and weights.
Until Trouve's trip on the Seine, in 1881, and the launch of the Electricity on the Thames, in 1882, very little was known concerning the history of electric navigation.
M. Trouve originally employed Plante's secondary battery, but afterward reverted to a bichromate battery of his own invention. In all the primary batteries hitherto applied with advantage, zinc has been used as the acting material. Where much power is required, the consumption of zinc amounts to a formidable item; it costs, in quantity, about 3d. per pound, and in a well arranged battery a definite quantity of zinc is transformed. The final effect of this transformation manifests itself in electrical energy, amounting to about 746 watts, or one electrical horse power for every two pounds of this metal consumed per hour. The cost of the exciting fluid varies, however, considerably; it may be a solution of salts, or it may be dilute acid. Considering the zinc by itself, the expense for five electrical or four mechanical horse power through an efficient motor, in a small launch, would be 2s. 6d. per hour. Many persons would willingly sacrifice 2s. 6d per hour for the convenience, but a great item connected with the employment of zinc batteries is in the exciting fluid, and the trouble of preparing the zinc plates frequently. The process of cleaning, amalgamating and refilling is so tedious, that the use of primary batteries for locomotive purposes is extremely limited. To recharge a Bunsen, Grove, or bichromate battery, capable of giving six or seven hours' work at the rate of five electrical horse power, would involve a good day's work for one man; no doubt he would consider himself entitled to a full day's wages, with the best appliances to assist him in the operation.
Several improved primary batteries have recently been brought out, which promise economical results. If the residual compound of zinc can be utilized, and sold at a good price, then the cost of such motive power may be reduced in proportion to the value of those by-products.
For the purpose of comparison, let us now employ the man who would otherwise clean and prepare the primary cells, at engine driving. We let him attend to a six horse power steam engine, boiler, and dynamo machine for charging 50 accumulators, each of a capacity of 370 ampere hours, or one horse power hour. The consumption of fuel will probably amount to 40 lb. per hour, which, at the rate of 18s. a ton, will give an expenditure of nearly 4d. per hour. The energy derived from coal in the accumulator costs, in the case of a supply of five electrical horse power for seven hours, 2s. 9d.; the energy derived from the zinc in a primary battery, supplying five electrical horse power for seven hours, would cost 17s. 3d.