piston inside the coring tube reduces distortion 

 to the upper layers of the core sample, promotes 

 greater penetration of the ocean floor, and, 

 according to some authorities, provides a more 

 representative sample of the bottom sediment 

 column in situ (fig. L-2). Piston-type corers 

 rigged without the piston mechanism are 

 gravity corers. Sometimes in an emergency 

 when a release mechanism is not available, 

 gravity corers are rigged without the device, 

 but the speed at which the corer sinks through 

 the water is limited by the payout speed of the 

 winch, and true free-fall speed is not achieved. 



L-5 The Phleger Corer. — The Phleger corer, 

 a gravity type, is designed to obtain cores up 

 to 4 feet in "length. It is widely used for collect- 

 ing marine sediments because of its small size 

 and weight. The corer has an overall length of 

 .3 or 5 feet — 3 feet if the 12-inch coring tube is 

 used, and 5 feet if the 3-foot is used. The corer, 

 usually, is operated from the oceanographic 

 winch using %2~ or %6-inch oceanographic 

 wire. 



The Phleger corer assembly consists of the 

 following components (fig. Ij-3) : 



The main weight (80 lbs.) comprised of the 

 upper tube, the main body weight, check valve, 

 tail fin assembly, and bail; 



LOWERING FREE FALL 



Coring tube, 12 and 36 inches ; 



A core catcher ; 



A cutting edge ; 



A release mechanism with a 20-foot chain ; 



A trigger line and weight ; 



Plastic (cellulose acetate butyrate (CAB) or 

 one of the new type, high density, low permea- 

 bility plastics) Imer, li/^ inches outside di- 

 ameter and end caps; 



Spare parts and 2 shipping cases. 



L-6 Instructions for Assembling and Op- 

 erating the Phleger Corer. — The Phleger corer 

 is simple to assemble and operate. The follow- 

 ing tools are required : 



Pliers, 8-inch combination ; 

 Pipe wrench; 

 Small hacksaw. 



Step 1. Screw the threaded end of the coring 

 tube into the main weight. 



Step 2. Examine the check valve and make 

 sure it is operating properly. 



Step 3. Insert a length of plastic liner into 

 the corer as far as it will go, and score a mark 

 on the plastic liner flush with the end of the cor- 

 ing tube. 



Step 4. Cut the plastic liner, with knife or 

 saw, approximately 14 inch shorter than 

 marked in step 3. 



PENETRATION HAULING IN 



RELEASE 



MECHANJSM 



ARM 



SEA Z 



BOTTOM 



Figure L-1. Principle of operation of gravity-type corers. 



L-2 



