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HYDROGRAPHIC MANUAL 



Page 462 



(4) The paper is held in true ahnement with Hmiting rollers, thus avoiding the 

 disadvantages of perforations. 



523. 808 Fathometer 



The 808 Fathometer is a semipor table, supersonic, graphic-recording, echo-sound- 

 ing instrument designed for hydrographic surveying in shallow to moderately deep water 

 from small vessels and launches. Its range is from % foot below the^s^ to 160 fathoms. 

 This instrument is manufactured by the Submarine Signal Company of Boston, Massa- 

 chusetts, from specifications prepared by the Coast and Geodetic Survey. Prior to 

 the introduction of the 808 Fathometer, soundings had been taken from small boats 

 and launches of the Coast and Geodetic Survey by using the leadline and wire sounding 

 machines. These methods were slow and at times inaccurate. 



Figure 100.— Launch hydrography using the 808 Falhdimti r 



The salient features of the 808 Fathometer are: 



(a) It is a semiportable instrument that can be installed in any small boat without the necessity 

 of cutting an opening in the hull, and without any complicated wiring or any of the other complica- 

 tions of a permanent installation. 



(6) The instrument may be permanently installed in any vessel by housing the transmitting and 

 receiving units properly inside the hull. 



(c) The practical depth range is from the least depth in which the vessel or launch will float to 

 160 fathoms under proper conditions. 



(d) Soundings may be recorded in feet or fathoms to accommodate the depth range and the 

 types of submarine relief encountered. 



(e) The range of the scale of the record paper is 55 divisions (feet or fathoms), and by means of a 

 phasing arrangement three other ranges may be recorded on the same scale, thus providing for an 

 expanded scale covering a depth range of to 160 (feet or fathoms). 



(/) A fast paper travel (about 2 inches per minute when recording in feet) to give a detailed record 

 (g) The use of a facsimile paper with printed depth scales for graphic recording. The paper does 

 not have to be moistened or chemically treated before or afterward, thus avoiding dimensional change. 



