the bottom, the removable cup is pushed back 

 releasing the catch on the nose lid and towing 

 arm. The nose lid snaps shut trapping sediment 

 in the cup, and the towing arm is rotated 

 forward. The latter movement shifts the 

 center of gravity, allowing the scoopfish to free 

 itself from the bottom and be raised without 

 end-over-end spinning. Once on deck, the cup 

 is removed, and for rapid sampling another cup 

 inserted, the nose lid and towing arm reset and 

 the scoopfish is ready for another lowering. 

 The sample from the cup is placed in a canvas 

 sample bag or mason jar and properly labeled. 

 When lowerings are completed the scoopfish 

 is washed down and all moving parts given a 

 coat of light machine oil. 



The scoopfish is used where a large number of 

 samples are to be obtained in a limited amount 

 of time. It has been used to record on the echo- 

 gram the type of bottom found while obtaining 

 soundings. 



6-66 DREDGES.— Dredges used aboard 

 Navy survey ships are based on a type designed 

 by the U. S. Navy Electronics Laboratory. 

 Bottom dredging operations require very sturdy 

 gear, particularly when dredging for rock 

 samples. The apparatus is constructed of 

 )i-inch steel plate, and is 1 foot deep, 2 feet 

 wide, and 3 feet long. The forward end is open, 

 but the aft end has a heavy grill of %-inch 

 round steel bars. This grill is designed to retain 

 large rock samples. When it is desired to obtain 

 finer sized material, a screen of heavy hardware 

 cloth is placed over the grill. A bridle consisting 

 of 7-foot lengths of galvanized steel chain or 

 K-inch wire is attached to shackling tabs on 

 the sides of the dredge. The bridle is attached 



to a swivel which is made fast to }^-inch diam- 

 eter lowering wire (fig. 6-13). 



During dredging operations, the ship is hove 

 to as the dredge is lowered. A boom or boat 

 crane, K-inch wire, and dynamometer similar 

 to that used for Ewing core operations is used. 



Towing the dredge along the bottom should 

 be done only by ships that can operate at very 

 slow speeds; i. e., at 2 or 3 knots. Ships which 

 cannot operate at such slow speeds can dredge 

 by drifting when wind and sea conditions 

 are favorable. 



During lowering, the dynamometer must be 

 watched for a decrease in tension indicating 

 the dredge has made contact with the bottom. 

 Then some extra wire is payed out to provide 

 scope for towing, and the winch stopped. In- 

 crease in dynamometer tension and wire angle 

 will indicate that the dredge is towing. A 

 careful watch of the tension must be kept. If 

 the tension is very irregular, showing decreases 

 in tension, the dredge is probably skipping on 

 the bottom. More wire should be payed out to 

 increase the scope. If rocky irregularities such 

 as ledges are encountered, the dredge will tend 

 to foul. If this occurs, the ship is stopped and 

 if possible reversed and maneuvered to free 

 the dredge. 



Rocks and representative samples of other 

 bottom material obtained should be packed in 

 a wooden box and properly labeled. The data 

 should be recorded on the M-Sheet. Samples 

 to be shipped to the Hydrographic Office are 

 to be addressed as follows: 

 The Hydrographer 

 U. S. Navy Hydrographic OflSce 

 Washington 25, D. C. 

 Attn: Code 5430. 



H. O. 607 



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