OCEAN ELECTRONIC NAVIGATIONAL AIDS 25 



on request will transmit signals to permit radio bearings being taken. 

 However, because of their dependable and convenient operating system, it is 

 more satisfactory in navigation to use bearings on the radiobeacons specially 

 established for this purpose. 



A number of cases have been reported of the indirect use of radio bearings 

 in navigation. A vessel equipped with a radio direction finder and knowing 

 its own position has been able to assist other vessels by means of radio bear- 

 ings. Thus, where a vessel seeking another in distress is unable to locate it 

 because of inaccurate reported position, neither having a radio direction 

 finder, a third vessel so equipped has been able to guide the rescuing vessel 

 by the use of radio bearings. 



There has, in the past, been discussion of the relative merits of using radio 

 bearings obtained from the ship and from fixed radio direction finder stations 

 on shore, but the question was of importance only in the development stage. 

 As soon as the improvement of the marine radio direction finder made prac- 

 ticable the obtaining of reliable radio bearings from the ship, the advantages 

 became apparent of having such a valuable navigational instrument located 

 so as to be directly available to the navigator for the various and general uses 

 to which it may be applied on shipboard. This system conforms to the stand- 

 ard practice of the sea in retaining the location of the navigating instruments 

 on the ship and placing the responsibility for their use and for the navigation 

 of the ship in the hands of the master. The navigator can use such checks 

 as he deems best, and knows what reliance to place on radio bearings in 

 comparison with his other means of guiding the vessel. Any number of ves- 

 sels properly equipped may take bearings simultaneously on a radiobeacon, 

 .iust as they can on a lighthouse, without interference with each other. The 

 United States Coast Guard no longer operates fixed direction finder stations. 



The direction finding equipment on shipboard (see fig. 2-5) has come to be 

 recognized as a navigational instrument essential to all larger vessels, and 

 has been extensively installed on smaller vessels. Its use tends directly to 

 economy of operation, and to increased safety. 



The International Conference on Safety of Life at Sea, held at London. 

 England, in 1948, prescribed that every ship of 1,600 tons gross tonnage and 

 upwards when engaged on international voyages must be provided with an 

 approved radio direction finding apparatus. 



The Communications Act of 1934 as amended and revised to September 1. 

 1948, requires that any passenger vessel of 5,000 tons gross tonnage and 

 upward navigating in the open sea be provided with an efficient radio direc- 

 tion finding apparatus. 



The use of radiobeacons greatly aids a navigator either to follow a desired 

 or prescribed course, or to avoid a congested route. It has been reported, 

 for example, that since this system came into service, steamers on Lake 

 Superior have been better able to adhere to the west- and east-bound traffic 

 lanes agreed upon on that lake. 



The use of radio bearings taken on board ship may result in considerable 

 saving of time. Besides the particular value of this in rescue and relief work, 

 it also increases the efficiency of operation of the vessel. It is frequently 

 possible by means of radiobeacon bearings to make port In fogs which 

 formerly have prevented the ship from proceeding. 



The use of radiobeacons on inland waters has received a thorough test on 

 the Great Lakes, Long Island and Vineyard Sounds, and Chesapeake Bay, 

 where it has proved most valuable. 



LOCATION AND DISTRIBUTfON OF RADIOBEACON STATIONS 



Radiobeacons are located at various sites (shore and marine) so that they 

 may be of utmost usefulness to the mariner in locating his position. (See fig. 

 2-2.) On account of their much greater range it is evident that the general 

 needs of navigation in this respect for any given length of coast have been 

 supplied by a much smaller number of stations than are required in respect 

 to lighthouses, or to sound fog signals. 



In the United States the radiobeacons are divided into four general classes, 

 as follows : 



Class A. — Reliable average range of 200 miles. 



Class B. — Reliable average range of 100 miles. 



Class C. — Reliable average range of 20 miles. 



Class D. — ^Reliable average range of 10 miles. 



