Ocean Depths Explored By Many Vessel

Sun (Auckland), Volume II, Issue 495, 26 October 1928, Page 13

Ocean Depths Explored By Many Vessel

Nations Employ Over 100 Ships for Work MODERN APPLIANCES USED Over in ' Fremantle the German naval survey ship Berlin has been in port after a long spell at sea. during which she has carried out a series of deep sea soundings of the waters lying between Australia and the East Indies (writes L. Rawson in the Melbourne ‘•Herald.*’) Up on the east coast the Australian naval survey ship Moresby continues month after month to survey and chart the myriad reefs and islets of the Great Barrier Reef, and all over the world the various Governments concerned maintain expensive survey vessels in the ceaseless task of mapping the unseen. Most people think the sea is as well mapped as the land, but in fact navigation, particularly if off the beaten track, is just a matter of steaming ahead and chancing any nasty surprise. The British Government maintains nine survey ships in various parts of the world, and altogether the various nations to-day have over 100 of these ships continually at work ferreting out the secrets of the ocean and its bed. They will have enough work mapping the unseen territory below’ the w’aves to keep them occupied for a thousand years to come. The worst of the sea bed, how* ever, is that it w’ill not “stay put.” Submerged volcanoes erupt with* startling suddenness, altering the soundings for perhaps an area of 1,000 miles; new’ islands appear in a night or grow slowly in the course of ages; a remote speck in the middle of the Atlantic (St. Paul’s Rock) is really the pinnacle peak of a mountain w r hich rivals the mighty Everest. The greatest known ocean depth is 32,089 feet off the Philippine Islands, compared w’ith Mount Everest’s 29,002. But whereas the average depth of the ocean floor is over 12.000 feet the mean height of the land above sea level is only 2.300 feet. In the old days they used to explore great depths with a heavy lead at the end of a long piano wire. Attached to the wire was a glass tube coated with chromate of silver. The pressure of the water forced it up the glass tube, discolouring the coating inside. The greater the height of the discoloured chromate the greater the depth, which was measured by means of a wooden scale. Nowadays the Sonic method is in use, based on echo sounding. The sound is transmitted from the ship to the bottom and is echoed back. The average velocity of sound in water is about 5,000 ft a second depending on depth, density* temperature, salinity, etc.

The interval between the despatch of the sound and its echoed return from the sea bed is accurately measured, but since this interval is usually a matter of a fraction of a. second the operation is one of cop* siderable nicety, and is not always successful. At the “Big Hole” off the Philippines the sound wave w’ould take over six seconds to reach the bottom and another six seconds to be reflected back, but in an ordinary sounding of, say, 50 fathoms, equal to' 300 feet, the time for the complete operation would be rather less than one-eighth of a second. Great depths contain no danger for the mariner. Provided there is ample water for his ship he is indifferent to the oceanic depths, but concealed pinnacle rocks are the greatest hidden dangers. They are so difficult to discover. If they lurk just below the surface they come tampering up to a point from a great depth like the tower of a cathedral. A ship may; pass over one a hundred times in a seaway, crashing down on the spire.

A few years ago a survey was made in a Massachusetts harbour, consist* ing of 91,000 soundings, many only 50-100 yards apart. But in that thicket of safe soundings lurked a pinnacle with its tip 18 feet below the surface. The U.S. cruiser Brooklyn, drawing 26 feet, found it, by steaming right on to NfO-w .