RELEASE 



LEVER 



ARM- 



CHAIN^ IQCORER 



LOWERING CABLE 

 RELEASE 



^> 



TRIGGER 

 WEIGHT 



v///////////////////////////////////////////m^ 



Figure 6-1. Principle of operation of free-fall corers. 



SEA BOTTOM 



2000M = D = DEPTH OF WATER 

 30° = a = SURFACE WIRE ANGLE 

 .866 = COSINE OF SURFACE WIRE ANGLE a 



X = ESTIMATED AMOUNT OF WIRE TO PAY OUT 



2000 . 

 X ' 



.866 = : 



-; X = 2309M 



Figure 6-2. Determining the amount of wire to pay 

 out from known wire angle. 



be payed out is, at best, an approximation. It 

 does not tell exactly how much wire is required 

 to reach bottom but affords a minimum and 

 maximum working range. The working range 

 is the difference between the least and greatest 

 amount of wire to be payed out. The larger 

 the wire angle the larger the difference will be; 

 conversely, the smaller the angle the smaller 

 the difference. In the example above, the 

 working range is 309 meters. Proper use of 

 this method requires close attention as the 

 apparatus nears the sonic or charted depth. 

 Erroneous estimates may result from incor- 

 rectly charted depths, errors in position, or 



H. O. 607 



350676 0—56 5 



drift of the ship to shallower water while on 

 station. Hence, caution must be exercised 

 before, during, and after the estimated wire 

 extent is reached. In practice, the bottom 

 generally is contacted after the minimmn 

 estimate is reached. 



6-8 CORING DEVICES.— Coring devices 

 are essentially steel tubes that are driven into 

 the ocean floor by gravity penetration. A 

 typical coring device consists of interchange- 

 able core tubes, a main body of streamlined 

 lead weights, and a tailfin assembly. The 

 latter is instrumental in directing the corer in 

 a vertical line normal to the bottom. The 

 main body, lead weights, and tailfin assembly 

 are referred to as the mainweight. 



6-9 Length of Cores. — The amount of 

 sediment collected by coring devices is depend- 

 ent upon the length of the corer, size of main- 

 weight, and penetrability of the bottom. The 

 minimum length of a core will be governed by 

 the general conditions of a given area. In 

 areas of predominantly rocky or hard bottoms, 

 it will not be possible to obtain a core of any 

 great length at any lowering. In such instances 

 it is well to make sure that failure to obtain a 

 core is due to the impenetrability of the bot- 

 tom rather than accidental blocking of the 

 corer by stray shell or stone. In other areas 

 the bottom may consist of such loose sand or 

 volcanic ash that the core catcher will not 

 retain the sample. When these conditions 

 exist it is best to use sonje other type of bot- 



53 



