are considered adequate to handle requirements anticipated by this 

 Office for such work. However, the larger dredges should be equipped 

 with simple pipe dredges for the recovery of material smaller than 

 the chain mesh and with fish-net liners. (See References X-22 and 

 X-34.) 



3. Corers 



Coring equipment in use by oceanographers at the present time 

 consists of three different basic designs: (1) the^ gravity-type, e.g. 

 Phleger, corer, (2) the piston-type, e.g. Kullenberg and Ewing, corers 

 and (3) the vacuum or hydro static- type corer, currently used only 

 by the Soviets. 



a. Gravity-type corer 



This type of corer is inexpensive to construct and simple to 

 operate. Cores over 16 feet long can be obtained with it under favorable 

 conditions, although lengths of six or ten feet are the more usual 

 maximum. The principal disadvantage of this type of corer is the low 

 recovery ratio (core length to penetration of the sediment). Further- 

 more, no unanimity of opinion exists on how to correlate the length 

 of the sediment core to the distance penetrated into the bottom. 

 (See References X-5, -10, -11, -27, -30, and -37o) 



The Phleger corer (Reference X-29) used by the Hydrographic 

 Office, which obtains cores with maximum lengths of about three 

 feet, is considered to be adequate for most reconnaissance needs. 

 However, the diameter of the liner is too small to allow an adequate 

 analysis of the engineering properties of the core. Also, the cutter 

 area ratio, C a *, of 67.5 percent is somewhat large. 



C a = 



D 2 - D 2 

 w ^e 



D e 2 



where C a = cutter area ratio 



D = outside diameter of core cutter 

 w 



D e = inside diameter of core cutter. 

 X-2 



