5233 HYDROGRAPHIC MANUAL PaGE 466 



black dots had been made on the gray surface. The dots are scarcely distinguishable 

 as such unless magnified and consequently the record appears as a rather broad band 

 with more or less sharp and smooth contour at the top, the bottom of the band fading 

 away gi'adually. The intensity of the record is somewhat proportional to the strength 

 of the echo. Figure 102 is a schematic wiring diagram of the amplifier and all other 

 electric connections. 



5233. Fathoiirani 



The graphic record of an echo-sounding instrument is called a fathogram. The 

 paper on which this is recorded on the 808 Fathometer is a standard type used for 

 facsimile reproduction. It has a black body coattxl a light gray on its upper surface, 

 the reverse side being metalized with alumiimm or copper for the purpose of elec- 

 tric contact. The paper is 7 mches wide and comes in 75-foot rolls on metal spools. 

 The printed scale is 6)4 inches wide, ruled horizontallj'" into 55 divisions, each repre- 

 senting 1 foot or 1 fathom, depending on which operating speed is used. Since the scale 

 of equal divisions lies along the arc of a circle traversed by the rotating stylus, the hori- 

 zontal graduations are closer together near the edges of the paper, but the distance 

 between fines, measured along the arc, is ji inch. The division lines are printed in 

 red, and four numerical scales of depth, to 55, 35 to 90, 70 to 125, and 105 to 160, 

 are printed alternately in red and green on the gray surface. The numerals correspond- 

 ing to the to 55 scale are printed in large red figures, those for the 35 to 90 scale in 

 large green figures, those for the 70 to 125 scale in small red figures, and those for the 

 105 to 160 scale in small green figures. The four phases are indicated by the letters 

 A, B, C, and D respectively, and at the shoal end of each scale the letter corresponding 

 to the respective phase is printed in color and size corresponding to the numerals of the 

 scale. The numerical scales are spaced about 1% inches apart and are repeated in the 

 above sequence. Regardless of which phase is being used, a corresponding numerical 

 scale will always be within 2}^ inches of any point of the record, facilitating easy reading. 

 While the fathogram is being recorded, the corresponding mimerical scale will not 

 always be visible, however, since only about 2% inches of it is visible at a time. A 

 notation of the phase in use must be made on the fathogram at the time. Depths 

 recorded in fathoms are generally distinguishable from those in feet, the former usually 

 being blacker and the trace of the stylus, along its natural arc, shorter. 



The travel speed of the fathogram paper under the stylus is 2 inches per minute 

 when recording in feet. Thus a 75-foot roll of paper will last 7K hours when sounding 

 in feet, or 45 hours when sounding in fathoms. 



Unlike some types, this paper is used dry, requu-mg no treatment before or after 

 recording. The new roll is installed in a holder beneath the stylus arm, whence the 

 fathogram paper passes to the right across the recorder platen to an automatic take-up 

 spool. These roll holders are secured to the inside of the cabinet door and are readily 

 accessible when the door is opened. 



Neither excessive heat nor humidity materially affects the dimensions or the color 

 of the paper. Aging tests show that the quality of the paper and the permanence of 

 the record are satisfactory. Tests were made to deteimine the dimensional change 

 in the paper with variations in humidity. From very dry to normal humidity the 

 change in width was 0.6 mm; from dry to saturation by steam it was 1.5 mm. In 

 terms of the fathogram scale this would mean a maximum of 0.5 foot in 55 feet, or 0.5 

 fathom in 55 fathoms, or slightly less than 1 percent change, under extremes probably 

 never encountered in practice. 



