Lost Voyagers

How Sofar

Locates Lost Voyagers

A “NEW” aid for shipwrecked mariners in the Pacific, with which the U.S. Navy has been ex perimenting, has been described in press despatches.

Actually, the system is not new: it has been in operation since the Pacific war. It is an extremely in teresting and rarely-mentioned res :ue aid, applicable to aircraft or shipping.

Known as SOFAR—from “sound ixing and ranging”—it is based on he fact that sound waves, as opposed :o radio waves, are capable of travel ing great distances in deep water.

Briefly: There are a number of widely-scattered “listening” stations, jach consisting of a microphone owered into deep water off a suit able coastline; the microphone is :onnected to an amplifier, and the amplifier records its output on a slowly-moving graph paper, as with ;he seismograph or the ordinary weather barograph (or recording parameter).

Normally, the recording pen shows only minor undulations. But when an under-water explosion accurs, a series of more pronounced peaks of sound are recorded. The arrival of the first of these normally sets off an alarm bell, to gain the attention of the personnel in charge.

Then, the recorded being capable )f measuring the time of arrival to a aundredth of a second, and the speed af sound through water being known, t is possible to determine with con siderable accuracy the distance of he sound-origin from the recorder.

In actual practice, the point charted by comparing the distances Torn three widely-separated listening stations is within a mile of the exact place of explosion, at distances of ip to 2,500 miles from the re orders.

THHE ship’s lifeboat, or the plane’s A rubber dinghy, is provided with i “bomb”—a cylinder 28 inches long md 3 inches in diameter, contain ng 4 lbs of TNT. Round the top }f the cylinder are six holes, each :apped by an ordinary crown-top.

Depending on the latitude the bomb s set to explode at from 1,500 to 1.000 feet (deepest at equator) by nerely removing the correct crown op with a bottle opener, and drop ping the bomb overboard—or from i plane about to “ditch.”

At last report, there were ouly

three recording stations in the Pacific —one at Kaneohe in the Hawaiian Islands, one at Point Arena, and the third at Point Sur, California. The recorders are usually maintained in conjunction with a radio station which is normally manned for 24 hours of the day.

On picking up a SOFAR signal, all stations compare graphs and quickly determine the fix by means of a radio “conference.”

It is believed that, as part of the International Civil Aviation Or ganisation, the Americans intend— if they have not already done so— to extend the recording chain to the Far East, thus covering the entire North Pacific. No doubt, South

Pacific Administrations will do the same, in due course.

Meanwhile, the “bombs” are in commercial production by the Edison