SCIENCE SIFTINGS

New Zealand Tablet, 29 April 1920, Page 46

SCIENCE SIFTINGS

• ♦ : (By "Volt.")

. ' ; Ships' Living Coats. A very expensive item in connection with the upkeep +i \ S u P * always been the cleaning of : the outside of the hull ~ from barnacles and other marine growths that coat the , outside of a vessel after a sea voyage. The long delay in cleaning vessels is one of the difficulties now experienced at the docks. .'.- i.l ? h n Present method is for an army of men to scrape the hull of the ship m dry dock, a process involving much time : The dry dock charges alone may amount to about fc1.85 a day in London, and while being cleaned the vessel is useless. ' Now, by a recent invention, which has been exhaustively tested at Portsmouth and Southampton, all this is to be changed. With the help of machinery, four men can now clean the hull of a vessel while it is still in the water, in about eight hours, and the loading or unloading or the ship can go on at the same time. It is expected that when the new method comes into general use a vast amount of time and hundreds of thousands of pounds will be saved. The apparatus consists of a frame carrying a revolving brush, worked by a submersible motor. A screw-propeller at the back of the frame forces the brush against the side of the vessel, and the barnacles are scraped off verv rapidly. f . " * Divers' Dangers. There is, at any rate, one post-war activity in which Britons have to take a back seat. That is as deep-sea divers in the work of salving vessels which have been sunk by mine or torpedo. It is here that the Jap shows his superiority. The Japanese diver can descend to a greater depth than the British diver, and, what is more, he will remain longer under the water without apparent injury to health. This is no mere boasting claim by the Japanese themselves; it is the rueful but truthful admission of an expert with a long association with marine salvage work. Few Japanese divers are engaged at work round the coasts of Britain, their activities in this direction being mostly confined to the Mediterranean. The greatest depth at which a British diver can work under water without doing himself a serious injury is from 20 to 22 fathoms— is, at the most, 130 ft below the surface. Even then our divers can remain only a comparatively short time at ' that depth, and they are obliged to descend and ascend very slowly to prevent the blood from gushing from their bodies. ■ _..- In some of the Government salvage ships what is known as a decompressing chamber is now provided, which the diver on ascending can enter and gradually become acclimatised to the natural atmosphere on the surface. A Japanese diver can work with comparative comfort at a depth of 27 or 28 fathoms, or nearly 170 ft below the point where the salvage ship is- moored, and as a rule he is not in such haste to give the signal to be hoisted up as his British colleague. Eastern fatalism enters largely- into the composition of these Japanese divers, and on this account the yellow men are inclined to take risks far below the surface which British divers, no less intrepid, would hesitate to take. Unexpected danger often confronts the deep-sea diver who has located a wreck which has been sent to the bottom by a torpedo. The pressure of the water frequently ~ has the effect of crumpling up parts of the vessel near the spot where the torpedo has shattered the sides, and sometimes even an ordinary touch will cause part of the splintered hull to collapse. The danger in such circumstances of being enveloped by a mass of wreckage is ever present. ■