24 



OCEAN ELECTRONIC NAVIGATIONAL AIDS 



excepting during fog, advantage should be taken of bearings at suitable angles 

 as opportunity offers. 



The common method of locating a ship by cross bearings may be employed 

 in radio navigation using two or more radiobeacons, or visual and radio bear- 

 ings in combination. Of course, the usual principles apply as to employing 

 stations which will give good intersections, and as to allowing for the distance 

 run between the times of taking bearings if the interval is appreciable. 



United States radiobeacons are operated at intervals on a fixed time 

 schedule in clear weather and continuously during fog; adjacent stations 

 send for successive minutes. This facilitates the taking of radio cross 

 bearings, as does also the location in important localities of two or three 

 stations sufficiently close for cross bearings. 



Radiobeacons in the approaches to New York, illustrating their use in 

 navigation, are shown in figure 2-3. Figure 2-4 illustrates how in actual 

 practice a navigator may fix his position by cross bearings on three Pacific 

 coast radiobeacons. The angles between the stations in figure 2-4 are not 

 such that a small triangle of most probable position will be formed as in 

 figure 2-3. Such cases are common along some steamship routes, but the 

 fixes are extremely valuable, nevertheless, and may be good despite the 

 small angle at which two of the lines cross. It will be noted that in figure 

 2-4 the correctness of the bearing of the station to the north is confirmed or 

 independently checked by that of the station to the south to give the distance 

 off-shore, while bearing of the station to ths east gives a cut at a good angle 

 to determine the progress of the vessel along the coast. 



For additional information on accuracy of bearings, plotting, and other 

 matters, the navigator should consult the current issue of H. O. Publication 

 No. 205, "Radio Navigational Aids." 



Radio bearings from a ship may, of course, be taken on any sending station 

 shown on the chart, transmitting on a frequency within the range of the 

 direction finder receiver. A considerable number of such radio stations 

 throughout the world have been listed on which bearings may be taken from 

 ships equipped with radio direction finder equipment. Many of these stations 



POSITION 

 OF SHIP 



\ "''S/^I SAN LUIS OBISPC 





FiQURH 2-4. — Determination of ship's position from three good radiobeacon bearings 



plotted on the chart. 



