THE BATHYKYMOGRAPH. A 

 DEPTH-TIME RECORDER 



by 

 Frank J. Hester, Donald C. Aasted, and Robert W. Gilkey 



ABSTRACT 



A device (bathykymograph) is described which records pressure (depth) on a 

 time scale. It is inexpensive, rugged, and easily calibrated. Operation, construc- 

 tion, and limits of accuracy are discussed. 



INTRODUCTION 



Tuna frequently escape under the leadline of 

 a purse seine (McNeely, 1961). To understand 

 this problem and perhaps to increase seining 

 success it is necessary to know the depth of 

 the leadline at any time during the fishing 

 operation. A device which records pressure 

 or water depth on a time scale was developed 

 to provide this information. This instrument 

 is called a bathykymograph due to its ability 

 to sense and record changes in pressure with 

 time. A patent application has been filed by 

 the U. S. Department of the Interior for the 

 senior author, who conceived the device and 

 was responsible for its development. 



CONSTRUCTION 



The BKG (bathykymograph) consists of four 

 assembly groups, three of which are shown in 

 figure 1. They are A - the pressure sensing 

 piston assembly, B - the piston housing, and 

 C - the case. The fourth group, the recording 



Note.--Frank J. Hesier. Fishery Research Biologist, 

 and Donald C. Aasted, Able Bodied Seaman, Bureau of 

 Commercial Fisheries Biological Laboratory, U, S. 

 Fish and Wildlife Service, San Diego, California; and 

 Robert W, Gilkey, Senior Laboratory Mechanician , 

 Scripps Institution of Oceanography, University of Cali- 

 fornia, La Jolla, California, 



assembly, is shown mounted on the piston 

 housing group (fig. 2). This construction is 

 illustrated in section in figure 3. The key to 

 figure 3 follows: 



1. A protective cover which guards the 

 threads on the end of the piston housing. Holes 

 allow the water to enter and leave freely the 

 space between the cover and the face of the 

 piston. This cover can be seen in place in 

 figure 2. For calibration purposes it is re- 

 placed by a cover equipped with an "O" ring 

 seal and a fitting for a pressure line and 

 gauge. 



2. "O" ring sealed piston. The diameter 

 of the piston depends upon the depth require- 

 ments of the instrument. Standard tolerances 

 for a reciprocating "O" ring seal are used. 



3. "O" ring seal between the piston hous- 

 ing assembly and the case. 



4. Paper clamp. 



5. Pressure sensitive paper. This paper 

 is on a roll inside the recording drum con- 

 centric with the piston housing. The free end 

 passes through a slot in the recording drum 

 and is wrapped once around the drum. The 

 paper is secured by tightening the wing screws 

 as illustrated. 



