The Phleger corer used at the Scripps Institution of Oceanography 

 has a cutter area ratio of 44 percent. As the cutter area ratio increases, 

 the penetration resistance of the sampler, the possibility of increasing 

 the recovery ratio to more than 100 percent, and the danger of sample 

 disturbance also increase. It is considered advisable to decrease the 

 outside diameter of the Hydrographic Office Phleger core cutter to 

 reduce the cutter area ratio to a value between 30 percent and 40 

 percent and to replace the metal flapper-type check valve by a rubber 

 stopper type which provides a better seal and usually allows the core 

 catcher to be eliminated. The elimination of the core catcher is neces- 

 sary for any engineering analyses of the sediment core. 



Longer cores having a larger diameter than those from the Phleger 

 corer can be obtained, if needed, by using a length of Kullenberg corer, 

 or other larger diameter pipe, with an attached weight stand, check 

 valve at the top, and a bail assembly. 



b, Piston-type corer 



The piston-type corer is the one most commonly used for 

 coring bottom sediments. At the Hydrographic Office both the Kullen- 

 berg and Ewing piston-type corers are used. The Kullenberg corer 

 has barrel lengths of six and 12 feet, a diameter of 1.875 inches 

 (inside diameter of the core liner), and a core cutter area ratio of 94 

 percent; the sample is contained in a cellulose acetate liner. The 

 Ewing core has barrel lengths of 20, 40, and 60 feet, an inside dia- 

 meter of 2.5 inches, and a core cutter area ratio of 99 percent; the 

 sample is contained in a metal pipe. 



Several basic questions are connected with piston coring, all of 

 which relate to the eventual use of the sediment core: (1) Does the 

 sediment core represent in situ conditions? (2) are the core diameter 

 and length adequate for the type of laboratory analysis required? and 

 (3) can the sediment be removed from the core barrel or liner without 

 introducing distortion or damage? (See References X-13 and X-32.) 



Until recently, slight distortional effects were not considered dele- 

 terious to the eventual use of the core which more often than not was 

 intended for geochronological studies. With the introduction of a 

 Hydrographic Office testing program designed to determine the engin- 

 eering properties of the sea floor, particularly as related to bearing 

 capacity, distortional effects and disturbance to the core became a 

 serious matter. 



X-3 



