SAILING "BLIND"

Evening Post, Volume CXVIII, Issue 143, 14 December 1934, Page 9

SAILING "BLIND"

RADIO NAVIGATION

Ships. frequently cross the ocean without • getting a glimpse 'of- the sun, moon, or stars by which'to calculate their latitude or ftngitude. In these circumstances they navigate solely by chart and compass, employing the method known as "dead- reckoning," writes Captain J. G. Bisset, 8.N.K., in the '^Daily Mail." This involves estimating the ship's speed aad making allowances for varying winds and currents, over a distance of, 3000 miles,: anfl is liable at times to considerable error. ■'' '" \ . V' ~'■-.''. ■ '. :;■ ■'.. In' pre-radio days, ''making the land" after such a voyage was a matter o? grave uncertainty—especially^ in thick weather—and much valuable time was lost groping about taking soundings and listening for fog-signals in an endeavour to establish the ship^ position.

■Now wireless has revolutionised this branch of navigation in.a way that few landsmen realise,

The captain of a ship approaching the Scilly Islands, which is the first landfall for most transatlantic shipping, can obtain radio bearings when 200 or 300 miles away by means of a, "direction finder" • instrument on the. bridge; it enables him to determine his exact position and to proceed on his voyage without delay.

The"D.F." instrument, as we call it, consists of a small loop aerial fitted to the top.of a metal pole about 12ft high. This aerial can be rotated as required by a horizontal hand-wheel placed over the top of a gyro-compass card.

The navigator listens with earphones for the signal of the particular radio, beacon he wishes to locate. On hearing it, he gently moves the handwheel and tunes the signal out to zero, the pointer attached to the wheel indicating the exact direction, or bearing, of the beacon. The signals are highpitched and distinctive.

, If bearings of two or three widely spaced beacons, such as Mizen Head (South . Ireland), Bound Island (Scillies), and Ushant (France), are taken about the same time, and the lines of bearing laid on the chart, their point of intersection gives the position of the ship. . Numerous radio beacons exist-today on prominent headlands round the coasts of all civilised countries. In thick weather they send forth their special signals continuously, and in clear weather twice every hour.

For the benefit; of ships not possessing "D.F." instruments, many coastal wifeless stations are so_ fitted, and will, on request, give any ship her own bearing- from the station. In most cases these stations work in groups of three- or four, and a ship requesting a bearing gets replies simultaneously from them all, enabling her to " fix '■'..' her position with accuracy. British stations make a charge of five shillings for this service. American and Canadian stations are free.

The fact that twelve Canadian "D.F." stations provided 41,625 such bearings during ,1931-32 -indicates the tremendous value of radio to all classes of shipping. Bearings taken from automatic radio beacons by navigators must exceed this number many times over. '