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Hawke's Bay Herald, Volume XXXV, Issue 11563, 16 June 1900, Page 2

AN "AIR JACKET" FOR STEAMERS. There may be said to be two limitations to the speed of steamships. The first may be termed the scientific or mechanioal limit. Great speed may be attained if speed is the only object, for a vessel may be filled with machinery for driving her. Some torpedo boats nearly answer to this desoription. In a less degree it also applies to men-of-war, where the consumption of coal is a secondary consideration. The other day a powerful modern cruiser, the Europa, arrived in Australian waters, her coal bill from London totalling ,£BOOO. But putting warships on one side, there is what may be called the commercial limit. Vessels run to earn money must have co much space for cargo and passengers, and this limits the space available both for engines and for coal. It is to improvements in boilers, engines, and other paraphernalia, therefore, that we must look for inoreased speed. Vast improvements have been made in boilers whioh now convert an astonishing amount of water into steam for every ton of coal used. Compound engines use the same steam two or three times over, and then it is returned to the boilers in the shape of water just below the boiling point, No one, however, supposes that the limit of efficiency has been reached. The trouble is that as speed is inoreased the friotion becomes so great that after a certain point it ia unprofitable. If this friotion oan be reduced then the present engines would give muoh greater speed. And it is just that whioh a Scotch engineer claims to have discovered, His method is to surround a moving vessel with an automatic "air-jacket." The device, oalled an " aspirator," which supplies the air, is described as being self-acting and without any moving parts. It is a V-shaped air ohannel, which passes down the vessel's stem as far as the keel, and in most cases goes a certain distance along the keel. This channel may be either inside or outside the vessel, and is provided with certain protected openings or ports constructed in such a way that the water rushing past them produces a minus pressure within them, and consequently draws out a continuous stream of air, which passing along the submerged surface of the ship, cuts off the immediate contact with the water, and therefore the water friotion. It is the olaim of the inventor that by means of his process a steamer makes her voyage in a continuous air-jacket. The air of course ultimately rises to the surface of the water, but if the ship be going at a fair degree of speed she will pass her whole length through the air current before it escapes. It is said that in the : experiments made with steamships on the ; Tay there was an inorease of speed ] amounting to from 21 to 20 por cent of j the ordinary Bpeod of tho ship, and it was < noted that tho groater porcontage of in- ' crease was in ships that had tho groater ' speed to begin with. '