FISHING GEAR AND FISHING METHODS 273 



The variety of sonar devices is startling, and more are being developed. 

 Among these are a low cost fish detector for the commercial fishermen. Sonar 

 machines are reported to be already in use on a few commercial fishing vessels 

 at West Coast ports. 



Although a few specially designed sonar ranging devices used by the Navy 

 revealed the presence of submarines more than 6 miles away, the average machine 

 has a lesser range. 



Sonar equipment costing less than a new net are now in the final stages of 

 development and are expected to pay for themselves, not only by helping to locate 

 fish, but also by revealing the rocks and wrecks on which costly nets are all too 

 often torn or lost. 



The echo-ranger is called sonar in this country and asdic in Great Britain. It 

 should not be confused with radar. The echo principle is the same, but wave 

 frequencies used in radar cannot be used under water. 



Radar. Radar might be referred to as one of the greatest marine surface-search- 

 ing aids ever to be developed. The perfection and practical applications of this 

 micro-wave navigating detector were hastened by 1941 war developments. 

 American ingenuity, intensified by the necessity of an all-out war effort, made it 

 possible to furnish the Navy with these "eyes" with which to work in detecting 

 the presence of an obscure enemy at sea or in the air. 



As a navigational aid radar is now rapidly growing in importance, not only in 

 our merchant marine fleet, but in the commercial fisheries as well. There are 

 already a few installations aboard tuna clippers. 



Loran (Long-range Navigation). Loran is an electronic system for accurately 

 determining the geographical position of a ship in any kind of weather. It is com- 

 parable to the telephone in that it enables the navigator to check his position 

 without leaving the chart room. Fixes are obtained from transmitting stations in 

 from 2 to 6 minutes, at distances of 750 nautical miles by day to 1400 by night. 



The loran system of navigation, akeady installed on many fishing vessels, 

 makes use of special transmitting stations on shore. It difi^ers from radar in that 

 no transmission takes place and no echo is received. Unlike the radio direction 

 finders loran measures the time, rather than the direction, of arrival of the signals. 



Transmitting stations on both coasts operate in pairs 200 to 400 miles apart, 

 designated as master and slave stations. It is relatively easy to operate loran equip- 

 ment since no knowledge of electronics is necessary. 



The master station starts the cycle of transmission by sending out a pulse which 

 reaches the slave station and at the same moment any loran receiver in its range. 

 This is repeated constantly 24 hours a day. Since each transmitting, or master, 

 station is identified by its radio frequency channel, a positive "fix" shows the 

 exact position of the vessel when two have been intercepted. 



Automatic Steering Devices and Suction Pumps. Additional equipment, de- 

 veloped within the past two decades and growing in popularity in the commercial 

 fisheries, should include the mention of automatic steering devices and suction 

 pumps for unloading fish cargoes. 



"Robot pilots," as automatic steering devices are sometimes called, operate 

 electrically without deviation from any fixed course on which it is set. Although 

 they must be set manually whenever changes in bearings are necessary, they have 



