Chapter 5— BATHYTHERMOGRAPH 



clear astern and it is safe to try again. The 

 operator must learn the feel of his own winch. 



With a little practice the BT can be brought 

 safely to within 2 or 3 feet of the towing block. 

 The winch motor should be turned off at this 

 point, eliminating the possibility of accidentally 

 jamming the BT against the towing block. Some 

 winches have a handcrank, permitting manual 

 rotation of the drum at this point. The BT can 

 then be brought aboard in various ways, de- 

 pending on how the boom is rigged. 



With the standard gate boom, the use of a 

 retrieving line and ring is recommended. This 

 line consists of a metal ring from 1 to 1-1/2 

 inches in diameter through which the wire is 

 passed between the towing block and the BT. 

 To the ring is attached a retrieving line, which 

 is secured to the lifeline or rail. With the 

 proper amount of slack, the ring rides freely 

 when the BT is being lowered and hoisted. By 

 hauling in on the retrieving line while easing 

 the brake, the BT can easily be brought to hand. 



If a retrieving line is not used, it will be 

 necessary to rig in the boom by casting off the 

 after guy and swinging the boom in with the 

 forward guy. Two men can pull it in with a 

 boathook — one man on the hook and the other 

 to slack the wire with the winch. If the boom 

 tops up, the BT can be brought aboard by one 

 man hauling in on the topping lift. 



Step 11 — Remove Slide and Secure Equipment 



As soon as the BT is in hand, move the sleeve 

 forward toward the nose to lift the stylus off 

 the slide. This action prevents the upper portion 

 of the trace from being affected by air tempera- 

 ture and becoming obscured as the instrvmient 

 is handled. 



Slack off the wire, place the BT in its deck 

 rack, and set the brake. Notify the bridge that 

 the BT is on deck. Partially eject the slide by 

 pushing against its edge with the forefinger, 

 the wire slide remover, or a pencil through the 

 slide-ejecting port. Grip the slide carefully by 

 the thumb and forefinger. Hold the slide only 

 by the edges, being careful not to obscure the 

 trace with smudges or fingerprints. 



If another lowering is to be made soon and 

 there is no danger of overheating the BT, it 

 may be left in the deck rack connected to the 

 wire. Otherwise, unshackle it and stow in a 

 cool place. 



CAUTION: Never let the temperature of the 

 BT exceed 105*^ (40.6°C). If this 

 temperature is exceeded, the cali- 

 bration of the instrument will be 

 damaged. Never leave the BT on 

 deck without protecting it from hot 

 sun. Suitable protection to the 

 thermal element can be effected 

 by keeping it covered with wet 

 cloths. 



Step 12 — Check Slide 



As soon as the slide is removed from the 

 BT, examine it to be sure that a suitable trace 

 was obtained. If the trace is smudged or oblit- 

 erated in any way, lower the BT again with a 

 fresh slide. 



Once a suitable slide is obtained, rinse it off 

 in fresh water, and label it according to the 

 directions given later in this text under the topic 

 heading "Marking BT Slide." 



PRECAUTIONS TO BE OBSERVED 



To obtain the greatest accuracy and prolong 

 the useful life of the BT, certain precautions 

 must be observed. They are discussed in the 

 ensuing topics. 



Disassembling BT 



Do not disassemble the BT, It is a precision 

 instrument, with delicate internal mechanisms. 

 Even with the greatest care possible, it is 

 difficult to avoid damage if disassembling is 

 attempted aboard ship. 



If, for any reason, the BT fails to operate 

 satisfactorily, it should be turned in for repair, 

 with a report indicating the symptoms to aid 

 the repair facility in correcting the trouble. 

 Standard failure reports also should be sub- 

 mitted in accordance with current directives. 



Maintenance of BT 



The BT is an accurate measuring instrument 

 and, although the construction is reasonably 

 rugged, the internal mechanisms are delicate. 

 Careful handling is essential to maintain the 

 accxtracy of the measuring elements. 



After each period of use, the BT should be 

 rinsed with fresh water. Never store a BT 

 that is being withdrawn from use without first 

 rinsing it thoroughly. 



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