AN INVISIBLE BREAKWATER.

Otago Witness, Issue 3442, 2 March 1920, Page 59

AN INVISIBLE BREAKWATER.

♦ THE BRASHER AIR SCREEN. An Invaluable Invention to Still Troubled Waters.—Multiplication of Small Porta Rendered Possible. —Protecting Eroded Foreshores.—A Solution of the St. Clair Problem. Mr Philip Brasher, an American engi-. neer, has invented an apparatus, known aa the Brasher Air Screen, consisting of pipelines, laid along the sea floor, through,, which compressed air is forced upward to the surface. The invisibly barrier of air overcomes the force; of the waves, and creates a lagooni of calm water in the roughest 6ea.. It . should be particularly valuable in protecting small harbours, and thus distributing sea-borne traffic, and opening up new and cheaper sites for manufacturing enterprises. It might also be applied to light-ships and life-boats, and to the preservation of foreshores exposed to coast erosion. The Brasher Air Screen was first tried with success in guarding the Standard Oil Company's new pier at El Se-. gundo, California, after half of it had been washed away. It was also used in salving the American steamer "Yankee," which grounded on rocks in heavy surf. Some particulars of the simple iiiven-. tion and probable methods of application are given' in. the Illustrated London News by A. E, Carey, M. Inst. C.E., F.C.S., F.G.S., who writes: —"Short cuts in harbour work are as a broad principle to be deprecated. Many ingenious devices have from time to time been evolved for securing protection from sea exposure, but have been found wanting in practice. i "The Brasher Air Screen, however, has ' successfully stood the test of actual experience, and appears to be coming expedient. The system is most effective in an oscillatory sea. It may perhaps be explained that there are two. cardinal groups of waves; (a) oscillatory waves, and (b) waves of translation. The oscilliatory wave is the open sea type. It is a carrier of force, the motion of the particles of such wave travelling in rolling circles, the movement of which at the top of the wave is onward, that at the trough of the wave backward, . there being an absence of motion at half height. It is obvious that the shattering '■ force developed by waves of this class necessitates formidable and costly structures to withstand its onslaught. If a simple and economical device could be adopted, by means of which" practical tranquillity might be secured during' rough weather, the advantages would Be enormous. "A ship entering a harbour protected by a line or lines of Brasher pipes is enabled to do so with safety. A light-ship or a lighthouse so protected would bo immune from severe sea conditions, and for salvage operations it has proved of vital value. The report of an eye-witness of the salving of a steamer under the lee shelter of a line of Brasher pipes reads as follows: 'The heavy breaking seas were powerless to pass the line of air. Before the air was turned 011 the seas were boarding the ship fore and aft, causing it to grind very much on the rocky bed, and making work very disagreeable. After the air was turned ort in the breakwater, it was as though the ship was in a lagoon formed by the breakwater, while seas were breaking heavily outside.' "It follows from the practical results now attained that there should be a great future for the Brasher Air Screen. There must be a vast number of localities on the English coast-line and in British colonies where the system might be employed to advantage." To the above it/ may be added that there are many places in New Zealand in which the' Brasher Air Screen should prove of immense value. If applied at St. Clair, near Dunedin, when the sand on the beach makes up again it should prove effective. It should also prove of service in protecting the foreshore at North Oamaru, where erosion caused sfjious results a few years ao-o. Then at IJokitika, where the seas threaten serious damage when rough weather prevails, the air breakwater mightprovide better protection than the groynes which were erected some years ago. Doubtless there are other places where the air screen might be given a trial. It might prove of service \t Hokitika, Greymouth, Westport, and it. rough weather at New Plymouth, Gifcjborne, ..and other places. It might prove in stabilising th© channel at the Nwi'River Heads, and j once again enable moderate sized craft to trade to and from Invercargill.