82 



HYDROGRAPHIC MANUAL 



Figure 27. — 808 type shoal water echo sounder. 



length of stylus arm is indicated when the 

 stylus and printed arcs do not coincide, the 

 center of rotation being correct. The length 

 can be checked by comparing the stylus arc 

 with arcs of various radii drawn on a plastic 

 sheet. The effective length should be correct 

 within 0.040 cm (0.010 inch). The effective 

 length varies with projections of the spring 

 stylus. Adjustment is provided in the stylus 

 holder trunion screws. The screws should be 

 locked, or sealed, to prevent movement, by 

 the lock screws in the back of the metal 

 frame holding the stylus. If the screw ad- 

 justment is insufficient, the bakelite insula- 

 tor can be shimmed or filed. 



3-93 Alignment of fathometer paper. — 



Since the 808 echo sounder is designed to 

 record soundings with a circular sweep, the 

 fathogram paper must be correctly positioned 

 with respect to the radius of rotation of 

 the stylus arm. The paper alignment is cor- 

 rect when the paper is moving across the 

 platen so that the extended centerline of the 

 paper will pass through the center of rota- 

 tion of the stylus arm and the paper moves 

 in a direction parallel with the lines on the 

 paper. The operator should occasionally 

 check the paper alignment by causing a fix 

 mark to follow one of the printed arcs on 

 the chart. If the fix mark follows the arc 



