OCEAN ELECTRONIC NAVIGATIONAL AIDS 



23 



It sends out signals by radio in all directions around the horizon, as does a 

 lighthouse by means of light beams, and it is distinguished from the neighbor- 

 ing signals by a definite characteristic, as is the light. 



The radiobeacon may be used as a leading mark for which to steer directly, 

 the navigator correcting the course from time to time by successive radio 

 bearings. Thus, such a signal off an entrance or other objectives may be 

 approached with certainty from a considerable distance. This is a valuable 

 use of radiobeacons, especially when these signals are located on lightships, 

 as illustrated by the signals on Nantucket Lightship and Ambrose Lightship, 

 which guide trans-Atlantic vessels to the approaches of New York Harbor. 



The signal emitted by a radiobeacon follows a great circle course. Radio 

 bearings may be plotted without applying a correction on a Mercator chart 

 if the difference in longitude involved is not in excess of 1° or 2°. When 

 the difference is larger, a correction usually must be applied which will be 

 found in H. O. Publication No. 205. "Radio Navigational Aids," under Radio 

 Bearing Conversion Tables. 



A bearing from a radiobeacon station may be combined with information 

 from other sources, as from an intersecting line of position from an astro- 

 nomical or Loran observation, from soundings, from dead reckoning, etc., to 

 locate the position of the vessel. 



A ship may also be located by radio bearings on a single radiobeacon by 

 taking two bearings on a station with an intervening period of time, and 

 plotting these with respect to the distance and course run between bearings. 

 With radio bearings, because the signals are not operating continuously 



NEW Y^K 



POSITKNI OF VCttCL 

 CROSS BEARI»«€S 



74» 



73* 



Figure 2-3.- 



-Radiobeacons in the approaches to New York and how they may be used by 

 vessels. 



