FOR some two or three years past there has been considerable academic discussion regarding the possibilities of propelling large vessels by an electrical system. Two Scottish electrical engineers, Messrs. Mavor and Coulson, of Glasgow, who have devoted considerable attention to this problem, have carried theory to a practical stage, a special vessel having been built by the Dumbarton shipbuilding firm of MacLaren Brothers, and equipped with the electric propulsion set which they have evolved for use with alternating current. Through the courtesy of the inventors we are enabled to describe the features and illustrate this interesting craft. The vessel measures 50 feet between perpendiculars; has a beam of 12 feet; molded depth of 7 feet 4 inches; a maximum draft of 4% feet, and is cer-Cfied by the Board of Trade to carry fifty passengers. It has been christened appropriately the “ Electric Arc." The mechanical equipment is carried out on the lines set out by Mr. M' avor in his paper, read before the Institution of Engineers and Shipbuilders in Scotland in February, 1908, and before the Institution of Civil Engineers in December, 1909. It comprises a six-cylinder Wolseley gasoline motor developing 45 brake horse-power, driving an alternating current dynamo with its exciter, the propeller being coupled to an alternating current motor. The switch gear is operated from the deck, or from the engine room, as desired. The inventors point out that although electric propulsion is not necessary or suitable for all vessels, yet in many cases it will form a convenient and economical addition to the power equipment of a ship. Hitherto electric transmission for marine propelling purposes has always been carried out upon the continuous current principle, but while this method is very convenient and suitable for small powers, its utilization offers serious difficulties in large installations. The inventors therefore maintain that alternating current motors alone are suited for the transmission of high powers at sea. They accordingly evolved their own lines upon which such should be applied, and the present large size model for actual practical experiments was constructed to demonstrate the possibilities and advantages of the system in regard to large vessels, and also to gain experience in details of application and handling of this equipment. The motor has no brushes or slip-rings. It is of the type known as the “ multiple wound machine,” in which there are in the present instance two independent windings. The current used is alternating three-phase. The generator is designed to give two power-circuits to the motor, to. represent the condition which would obtain more usually when larger powers were involved and where two or more generators would be in use for the full power. The first combination of generator and motor windings gives full speed of 7.25 knots, and the second combination about two-thirds of full speed— about 5 knots. The power applied to the propeller is determined by the electric control, which in the present case is put in the hands of the navigator and operated from the bridge. The first trials with the “ Electric Arc” proved eminently successful. It was run over the measured mile in the Gareloch, the tests comprising the stopping, starting, speed-changing, reversing and maneuvering qualities of the vessel. The mean speed attained was 7.25 knots, with the propeller making 415 revolutions per minute. The current readings showed that about 25 brake horse-power was delivered to the propeller shaft at full speed, and that 35 brake horse-power was developed by the engine running rather below the rated speed. The maneuvering capabilities of the boat were very strongly emphasized, the propeller being reversed from ahead to astern and vice versa time after time. The reversing operations were equally striking, it being shown possible to throw the switch from “ full speed ahead” to “ full speed astern,” or vice versa, without running any risk of damaging the machinery. Though such a sudden change would not be required in actual practice, it offered a severe test of the capabilities of the electrical system. The experiments are to be continued, and the success achieved so far has resulted in greater interest being centered in the possibility of adapting electrical propulsion to large vessels. Fish Pastes Abroad EXPERTS in the United States are giving careful study to the methods in vogue in certain fish factories in northern Europe, with a view to the economical preparation of products from fish that hitherto Americans have regarded as useless. Among these is the preparation of fish-pastes from fish that have no commercial value either as fresh or salted food, but which, at the same time, possess a high nutritive value. It is said that the flesh of both the shark and the whale (which latter, however, cannot, Of course, ba properly classified as a fish) are largely utilized for the preparation of a fish-extract that resembles in some respects the popular extracts of beef, being at the same time far cheaper. All fishy flavor is eliminated by chemical processes, and the extract is valuable for the foundation of soaps and in general cookery. Whale meat is very nutritious, but its excessive amount of fat renders it unpalatable to most persons. So this fat is removed before the extract is boiled down to a syrupy consistence and sealed in jars. In many of the fish factories of Norway a “ fish-meal” is made that is eaten extensively by the nations of northern Europe. In these several ways fish which were formerly rejected as being unfit for food are being utilized to the advantage of many. Trees and Men IT has been calculated that a single tree is able through its leaves to purify the air from the carbonic acid arising from the perspiration of a considerable number of men, perhaps a dozen or even more. The volume of carbonic acid exhaled by a human being in the course of twenty-four hours is put at about 100 gallons; but by Boussingault' s estimate, a single square yard of leaf-surface, counting both the upper and the under sides of the leaves, can, under favorable circumstances, decompose at least a gallon of carbonic acid in a day. One hundred square yards of leaf-surface then would suffice to keep the air pure for one man, but the leaves of a tree of moderate size present a surface of many hundred square yards.
This article was originally published with the title "The “ Electric Arc”" in Scientific American 105, 6, 116 (August 1911)