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ECHO SOUNDING 



5231 



(h) A fix marker by which any event (e. g., a sextant fix) may be recorded on the fathogram. 

 (i) Supersonic magnetostrictive transmitting and receiving units. 

 (j) A single 12-volt storage battery supplies all necessary power. 



The 808 Fathometer is composed of three separate units: a streamHned sub- 

 mersible housing (called the Jish) containing the acoustic transmitting and receiving 

 units; a recorder cabinet containing the graphic-recording mechanism, keying mecha- 

 nism, and the echo amplifier; and a 12-volt storage battery. All these units can be 

 installed in or removed from a launch equipped for them in a short time at the beginning 

 or end of the working day. The fish is secured over the side of the launch; the recorder 

 cabinet is secured to a thwart or bulkhead in some protected part in the launch; and the 

 batteries should be installed in a specially prepared wooden box lined with sheet lead. 



Figure 101.— Fish of 808 Fathometer mounted on hydrographic launch. 



5231. Acoustic Transmitting and Receiving Units 



The Jish is a mahogany casing about 30 inches long by 8 inches square, projectile- 

 shaped at the ends to ensure nearly streamlined motion through the water. The weight 

 of the fish is about 80 pounds out of water and 30 pounds when submerged. A portion 

 of the bottom of the fish is hollowed out and a brass casting inserted to support the 

 magnetostrictive transmitting and receiving units. Tlie underside of the casting is 

 closed by two thin metal plates, through which small holes have been punched to allow 

 the cavity containing the transmitting and receiving units to fill with water. The units 

 are identical, each consisting of a bundle of rectangular nickel laminations. Each unit 

 is approximately 6 by 4 by 3% inches in size. Each lamination is approximately 4 by 

 3% inches by a few thousandths of an inch thick. Three rectangular openings are 



