sounding lead by means of a hole drilled in the 

 lead. The jaws are actuated by a sprinij, and the 

 tension on the spring can be adjusted by tight- 

 ening or loosening a screwcap. The jaws are 

 held open by engaging two trigger pins witli- 

 iu the jaws. Tlie mud snapper may be operated 

 in shallow water by hand lowering or it may be 

 lowered from a bathythermograph or oceano- 

 graphic winch. 



Samples are placed in sample jars, and 

 labeled, and the operation is recorded on the 

 Oceanographic Log Sheet-M. 



Very little maintenance is required for the 

 clamshell snapjjers. After the operation is com- 

 pleted, wash off any remaining sediment, rinse 

 in fresh water, dry, and lubricate any moving 

 parts. 



haSBT- -W 



Figure L-19. Clam.sheU snapper. 



L-36 The Scoopfish Underway Bottom Sam- 

 pler. — The Scoopfish (fig. L-20) is designed to 

 obtain a samjole without stopping the ship. It 

 is ideal for rapid reconnaissance sampling of 

 surface sediments, but it does not adequately 

 sample very coarse (gravel or larger) sedi- 

 ments. The sampler weighs 11 pounds and is 15 

 inches long. It has the capacity to collect 10 

 cubic inches of bottom sediment. It is lowered 

 from the bathythermograph winch in depths 

 less than 100 fathoms from a ship underway at 

 speeds not over 15 knots. When lowering, care 

 must be taken that the nose lid is not prema- 

 turely tripped as the sampler enters the water. 

 The scoopfish is allowed to fall freely in the 

 same manner as the bathythermograph (see 



During the samplers descent, the towing arm 

 is engaged toward the rear, and the nose lid is 

 hooked back in open position. "WHien the scoop- 

 fish strikes the bottom, the samjile cup is pushed 

 back releasing the catch on the nose lid and the 

 towing arm. The nose lid snaps shut trapping 

 the sediment sample, and the towing ami ro- 

 tates forward. The latter movement shifts the 

 center of gravity, allowing the scoopfish to free 

 itself fi-om 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 lowered at once. The sediment 

 sample from the cup is placed in a jar and 

 labeled, and the operation is recorded on the 

 oceanographic Log Sheet-M. Wlien lowerings 

 are completed the scoopfish is washed down and 

 all moving parts are lubricated. 



The scoopfish is used where numerous sam 

 pies are to be obtained in a limited time. 



Figure L-20. Scoopfl.sh underway sampler. 



L-37 The Van Veen Bottom Sampler.— The 



Van Veen bottom sampler is shown in figure 

 L-21. It weighs approximately 74 i^ounds and is 

 capable of collecting 200 or 300 cubic inches of 

 sediment sample. Because the jaws of the 

 sampler overlap, a sample obtained from con- 

 siderable depth can be brought to the surface 

 with little loss by washout. 



To operate the Van Veen sampler, rig the 

 cradle as shown in figure L-21. The sampler 

 trigger hook has been modified to facilitate 

 sampling. 



In lowering the sami^ler, care must be ex- 

 ercised as it is entering the water because any 

 appreciable decrease of tension on the lower- 

 ing wire will trip the sampler prematurely. 

 Lowering speed should be maintained at about 

 60 meters per minute. 



Van Veen bottom samples are placed in jars 

 or canvas bags and labeled, and the operation is 

 recorded on the oceanographic Log Sheet-M. 

 When lowerings are completed, the sampler is 

 rinsed with fresh water, dried, and all moving 

 parts are lubricated. 



L-38 Dredges. — Dredging operations for bot- 

 tom sediments, usually, are conducted only when 

 coring and grab sample devices have failed to 

 obtain a bottom sample. Dredges used aboard 

 U.S. Naval Oceanographic survey ships include 

 triangular shaped, box shaped (fig. L-22), and 

 pipe dredges. 



Dredges are constructed of 14-iiicb or heavier 

 steel plate, and they vary in size and weight. 

 The forward end fif the dredge is open and the 

 aft end is co\ered with a hea\y grill which is 

 designed to retain a certain size material. 



1^17 



