DANGEROUS ROCKS

Evening Star, Issue 20373, 3 January 1930, Page 9

DANGEROUS ROCKS

WARSHIP’S CHARTING TRIP MODERN PLUMBING METHODS. , When “swinging the lead” was superseded in the Navy a picturesque part of the sailor’s work ceased, but the modern methods of plumbing the depths of the ocean gain interest from their wonderful ingenuity (said the Sydney ‘Morning Herald’ recently). H.M.A.S. Moresby arrived at Sydney from a surveying trip undgr, Commander D. A. Henderson. Nearly 1,000 square miles of the ocean floor was accurately charted, and dangerous shoals were located-, without necessitating the dropping of a single lino to the bottom. This accurate measurement of the ocean depths was accomplished by the use of the echo sounding machine. As the vessel made its way backwards and forwards over the area to bo surveyed a little metal hammer on one side of the boat was tap, tap, tapping against a metal anvil, and on the other side the sensitive ears of a microphone picked up the sound waves after they echoed back from the bottom of the sea.

As the rapidity of the sound waves in sea water is known to a nicety, the depth of the water at any spot under the vessel was read by an operator at the microphone: as simply as reading the time from a dock. Of course, minor adjustments are often necessary, because the speed of the sound waves varies slightly according to tho quality of water —salt, fresh, or brackish—and is also upset by changes in temperature. The Moresby charted 358 square miles at Flat Top, off tho mouth of the Pioneer River at Mackay, and 434 miles at North Reef. Other areas near Percy Island wore also examined. Many uncharted reefs were found that lay directly in the path of shipping. Off the Percy islands one ’ rock was found only 21t beneath the surface. This rock had almost accounted for the lighthouse steamer Cape York, which struck the rock a glancing blow. The vessel was flung to tho side as she scraped past, but if she had met tlio rock head on tho consequences would have been disastrous. Another rock was found near Percy Island, where the surf had been noticed boiling by passing ships. This was called the Goodwin Shoal, in honour of the Governor of Queensland. Other useful work was done at Dedele, in Papua, where the Morinda had struck a rock in a narrow, tortuous passage. When tho Moresby returned the channel had been mapped, and was safe for shipping. • As the bronzed seamen hurried clown the gang plank on the leave they had so eagerly awaited for nearly eight months, there was no doubt that they had benefited by tho trip. “ Have you seen my men,’’ said Commander Henderson proudly. “ I worked them hard. A surveying ship is no child’s play; but you can aeo how fit they are after their work in the tropics.”