Chapter 5 — BATHYTHERMOGRAPH 



35.156 

 Figure 5-1. — Depth-sound speed measuring set AN/BQH-IA. 



are precalculated for various classes of sub- 

 marines. Charts must be selected with isoballast 

 lines printed for that particular class of sub- 

 marine. In indicating a trace that crosses the 

 isoballast lines, action of the pen and drum gives 

 the amount of water to pump or flood in order to 

 maintain the submarine's trim. 



Buoyancy changes, indicated by crossings of 

 isoballast lines, may be related to submarine 

 depth and also to velocity of sound in water. 

 Both submarine buoyancy (upon which trim de- 

 pends) and velocity of sound in water are definite 

 functions of salinity, temperature, and pressure. 

 Inasmuch as a moving submarine encounters 



changing conditions of salinity, temperature, and 

 pressure, the AN/BQH-lA recording equipment 

 must measure these changes in terms of absolute 

 values of velocity of sound in water. Sensitivity 

 of the velocity-measuring portion of this equip- 

 ment is sufficient to indicate changes in sound 

 velocity of 1 fps when passing through a thermal 

 gradient. Equipmentpressure circuits are capable 

 of indicating changes in depth of approximately 

 1 foot. This measurement represents the mini- 

 mum readable definition of the recorder chart's 

 pressure portion. 



Isoballast curves are calculated in such away 

 that individual curves pass through all points 



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