156 • Marine Minerals: Exploring Our New Ocean Frontier 



Photo credits: U.S. Bureau of Mines, U.S. Geological Survey 



Chain bag dredge 

 Dredges Used for Sampling the Seafloor 



corers use acoustical or mechanical vibrations to 

 penetrate material.^' 



An example of an impact coring device is the box 

 core. An advantage of this type of sampling sys- 

 tem is that it retrieves relatively undisturbed cores. 

 A disadvantage is that a box corer is capable of sam- 

 pling only the top few feet of an unconsolidated de- 

 posit. It is rarely used in sand because penetration 

 requires additional vibratory or percussive action. 



Grab dredge 



Well-known percussion drilling devices include 

 the Becker Hammer Drill and the Amdril series of 

 drills. The Becker drill penetrates sediment using 

 a diesel-powered hammer that strikes a drill pipe 

 91 times per minute. It also uses reverse circula- 

 tion, meaning that air and/or water is pumped 

 down the annulus between the inner and outer drill 

 pipes, continuously flushing sample cuttings to the 

 surface through the inner pipe.^^ Among the advan- 

 tages of the Becker drill are: its capability to re- 

 cover all types of deposits, including gravel, sand, 

 boulders, and clay; its ability to drill in a combined 

 depth of water and sediments up to about 150 feet; 

 and its capacity to recover representative samples. 

 However, open water use of the Becker drill is slow 

 and relatively expensive. 



The Becker drill is rated by some*^ as one the 

 best existing systems for offshore quantitative sam- 



^'M.S. Baramand W. hee, Marine Mining of the Continental Shelf: 

 Legal, Technical and Environmental Considerations (Cambridge, 

 MA: Ballinger Publishing Co., 1978), p. 70. 



"Dimock, "An Assessment of Alluvial Sampling Systems," p. 10. 

 "Ibid., p. 55. 



