Assemble the trigger weight corer in the 

 same manner as described in section 6-15. 

 Attach the trigger line to the trigger weight 

 and the end of the release arm. Adjust the 

 length of the trigger line so that the trigger 

 weight will be suspended 14 feet below the 

 cutting edge of the Ewing corer nosepiece. 

 This length may have to be adjusted slightly 

 one way or the other. The proper length of 

 trigger line depends upon the speed at which 

 the winch can be stopped, the rate at which 

 the wire is payed out, and the amount of "recoil" 

 in the wire when the corer is released. If the 

 trigger line is too short, sediment will get into 

 the piston. If the line is too long, then several 

 feet of water will be cored before the tube enters 

 the sediment. For proper operation, the 

 piston must take up the slack in the wire and 

 stop one foot above the ocean bottom. 



6-48 Rigging for Lowering. — The methods 

 for suspending the Ewing piston corer over the 

 side will vary depending upon the equipment 

 available aboard ship. Because of the size 

 and weight of the corer, the operation requires 

 the use of a cargo boom or boat crane equipped 

 with a swivel hook. It is recommended that a 

 wire rope sling be spliced just above and below 

 the lead drive weights. The boom or crane 

 hook can be hooked into the sling and the 

 corer hoisted up and over the side in a hori- 

 zontal position. The coring tube is then 

 lowered into the water with handling lines and 

 the hook lowered until the entire assembly is 

 suspended vertically from the lowering wire. 

 The hook then can be released from the sling 

 and hoisted clear of the gear. Lower the 

 trigger weight over the side. Check to see 

 that the trigger weight and line is tending 

 properly and the corer is suspended correctly 

 from the release mechanism. It is important 

 now to remove the safety pin from the release 

 arm. Rig out the boom or crane until the 

 corer is in the lowering position and lower 

 the corer to the water's edge. Set the meter 

 wheel or dynamometer counter to zero. Com- 

 mence lowering. 



6-49 Obtaining the Core. — When lowering, 

 it is important to keep a careful check on the 

 depth at all times, especially as the corer nears 

 the bottom. Close attention must be paid to 

 the amount of wire out and to the dynamometer 

 reading for indication of striking bottom (fig. 

 6-8). Contact is indicated by a sudden mo- 

 mentary drop in wire tension. When this drop 

 in tension is noted, the winch must be stopped 

 immediately to insure proper operation of the 

 piston and to prevent the wire from piling up 

 on the bottom. Piled up wire will kink, causing 



64 



damage to the wire and possible loss of equipment. 

 Upon reaching the bottom, the tr-gger weight will 

 strike first, producing a slack in the trigger line 

 and activating the release mechanism. This 

 allows the Ewing corer to fall and penetrate the 

 sea bottom. As soon as the winch is stopped, 

 reverse controls and commence hoisting. 



6-50 Retrieving the Core. — During the pull- 

 out, that period while the corer is being freed 

 from the bottom, watch the dynamometer 

 closely. Have all hands stand clear of the wire. 

 Be ready to stop the winch the instant tension 

 appears excessive. Normally, the pull-out ten- 

 sion is in the order of two to four thousand 

 pounds greater than the tension just prior to 

 free fall. When free of the bottom, the tension 

 usually will drop to approximately one thousand 

 pounds greater than that just prior to free fall. 

 It is advisable to cease hoisting should the 

 tension become excessive. When tension has 

 decreased, hoisting may be started again. Dur- 

 ing hoisting, the piston stop collar supports the 

 entire weight of the corer. 



When the release mechanism has surfaced, 

 rig in the boom or crane and bring the gear to 

 deck working level. Hoist aboard the trigger 

 weight and detach the release mechanism from 

 the wire. Next bring the mainweight to deck 

 working level and insert the swivel hook into the 

 sling on the mainweight. Take a strain with the 

 hook and slack the lowering cable in order to 

 raise the coring tube to a horizontal position. 

 The tube is raised with handling lines. When 

 level, bring the corer inboard and lower it to 

 the deck. It is recommended that the main- 

 weight be placed in a cradle to prevent it from 

 rolling on the deck. Release the hook and 

 secure the boom or crane (fig. 6-9). 



6-51 Removing the Core Sample and Re- 

 cording the Data. — The trigger-weight coring 

 tube takes a core which is of greatest importance 

 in determining the surface sediment of the ocean 

 floor. This cannot be determined from the top 

 of the main core because that part usually is 

 unconsolidated and becomes badly distorted 

 when the core is laid on its side. The contents 

 of the cutting edge and core catcher of the main 

 coring tube also are of great importance; they 

 represent the material found at the deepest 

 penetration. In many cases, full-length pene- 

 tration of the coring tube is stopped short by 

 striking firmer sediment or hard rock. In such 

 an instance the harder sediment is likely to be 

 much older than that which overlies it and, 

 therefore, will furnish information of greatest 

 value for marine geology and sound propagation 

 studies. Since such material is often penetrated 

 but a few inches, all evidence of it may be lost if 



H. O. 607 



