SCIENCE OF NAVIGATION

Rotorua Morning Post, Volume 2, Issue 271, 11 July 1932, Page 2

SCIENCE OF NAVIGATION

MODERN METHODS PROVIDE MANY tNGENIOUS * DEVICES. " THE VALUE OF WIRELESS. The part science plays in moderh navigational methods was described by Captain W. J. Keane, of the Marine Department, during a * lecture to yachtsmen recently. Devices used by seamen to bring their sbips safely through fogs were .also interestmgly outlined. The real testing of the navigator comes in a fog, said Captain Keane, and many ingenious devices have been invented to help him. They are based on sound which' is transmitted through air, water or ether. Sound through the air is picked up by ear, through the water, by si sys;tem of hydraphones,- usually fitted into the bows of the vessel, and connected to the navigating bridge hy telephones, and the wireless wave is picked up hy th'e wireless receiver. Direction is found from sound through th'6' air, the speaker continued, by means »of the compass, and in prractice can he estimated with a fair degree of accuracy. Having fixed the direction line from a fog signal, the navigator can very often establish his position on that line by the depth of water, and on well survsyed coasts the method of "feeling" his way along by frequent use of the lead in finding the depth of water and nature of the bottom is still commonly used by the coastal navigator. Sortnd through the water is more reliable and travels nearly five times as fast as sound through the air, and is usually transmitted hy a submarine hell attached to a buoy or light-ship. The direction of the source of this sound is found by means of hydraphones placed in each how of the ship and independently connected to the navigating bridge by means of a telephone. Then if the navigator hears the sound in one telephone without hearing it in the other he knows that the submarine bell is somewhere on the how indicated by the phone in which he hears the signal. To establish a definite line of position he alters the course of the ship until the signal is heaffd in both phones with the same degree of strength. His vessel is then pointing toward the source of the signal and from that he gets a definite line of direction. The methods used in visual navigation can then be employed in using the direction lines so found to the best advantage. Accuracy of Sound. The degree of accuracy with which sound through water can he used is demonstrated in the echo depth-find-er, the principle of which is the sending out of sound from the bottom of a vessel and recording the echo also which is reflected back from the bottom of the sea. The time taken between the sound being transmitted and the echo being recorded is measured by electrical apparatus and the depth is at once given. By this method a continuous record of the depth can be obtained, and some machines print the depths found on a graph and so a permanent record of any line of depths taken is thus obtained. Wireless plays a big part in navigation, and the wireless direction finder is also a valuable aid to navigation in thick or foggy weather. This aid to navigation forms part of the navigational equipment of practically all modern ships, and under the new International Safety Convention which will come into force next year, it will be compulsory for all passsenger ships on international voyages to be equipped with this appliance. An ingenious position finder has lately been established on the coast of Great Britain, in which the combined use of a wireless telephone and an ordinary fog signal is made to ascertain the ship's p-osition. 2t is known as the talking beacon. An ordinary fog signal is sounded, and approximately 5 seconds after, the wireless telephone eombined with a gramophone begins to count one, two, three, etc., at approximately 5 seconds' intervals. Speed of Wireless Signals. An observer listens for the ordinary fog signal, and when he hears it noteo the figure which is received by hn, wireless receiver. If he hears the figure 5 he at once knows he is five miles from the source of the signal. and having also obtained his direction, knows, tberefore, the ship's position. The principle underlying this devic-e is that sound travels 1090 feec ncr second, or takes nearly 5 seconds travel a mile. A wireless signal tiavels at the same rata as light, viz., 186,000 milfes per second, and therefore, for practical purpioses, the sending of it and the receiving of it can be said to be simultaneous. The wire- 1 less telephonic apparatus is started 1 Wheri the fog signal is given and tberefore counts the miles the sound signal travels to reach the observer. Another method employed to guide a vessel in fog in narrow waters such as the entrance to a harbour or narrow channel is the "leader" cable. This is a cable which is laid on the bed of the sea in the middle of the channel. An electrical current is sent along the cable, and by means of recording apparatus installed in the bottom of the vessel the position j of the ship in reference to the cable I can he ascertained. /