it.y or piston, should be lowered to near the bot- 

 tom at a medium speed. Wlien near the bottom, 

 slow the winch and lower until an indication is 

 observed that the release meciuuiism has trip- 

 ]ied; then, stop the winch, note the time and the 

 amount of wire out, and commence haulino- in 

 immediately. 



In order to ascertain when the corer has 

 reached bottom, the oceanographer should (1) 

 estimate the amount of wire that will be re- 

 quired to reach the bottom taking into con- 

 sideration any wire angle resulting from the 

 ship's drift (2) observe carefully the tension 

 on the lowering wire when it is estimated that 

 the corer is nearing tlie bottom. 



1. How to determine tlie amount of wire to 

 pay out from the wire angle. — Frequently dur- 

 ing bottom sampling ojjerations, high wire 

 angles occur as a result of the ship's drift. It is 

 necessary to know how much wire to pay out so 

 that the corer will reach the bottom without 

 laying an excessive amount of wire. "Wlien wire 

 is layed on the bottom, it usually kinks so badly 

 that the kinked portion litis to be cut ofi". By 

 using the cosine of the surface wire angle and 

 the sonic or charted depth, the approximate 

 amount of wire needed to reach bottom can be 

 estimated. Figure L-13 illustrates the problem. 



DRIFT 



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 



COS a = ^; COS 30° = - 



Figure L-13. Determining the amount of wire to pay 

 out from known wire angle. 



This method of estimating the amount of wire to 

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

 does not give exactly how much wire is recjuired 

 to reach bottom, but it affords a minimum and a 

 maximum working range. 



•2. How to determine when bottom lias been 

 reached l>y observing wire tension. As the corer 

 is lowered, the wire will exert a steady pressure 

 on the block, and an indication that bottom has 

 been reached will be obser^'ed when tension is 

 relaxed owinsc to wire slack. 



In shallow waters, a simple spring scale and 

 block may be used to observe wire tension (fig. 

 L-14). The block is placed on the winch wire; 

 the spring end is secured to a rigid part of the 

 ship, such as a rail stanchion; and tension on 

 the wire is observed as the wire is payed out. 



In deep water operations, deep sea dynamom- 

 eters are used to record tension on the wire. 

 Some of the.se are built into the oceanographic 

 winches others are rigged for the operation (fig. 

 Lf-15). When the tripping weight strikes the 

 bottom, it i-eleases the corer; the free fall of the 

 corer causes the wire to slacken and the spring 

 scale or dynamometer to indicate a reduction in 

 tension. The instant the tension is relaxed owing 

 to slack wire, stop the winch, reverse the con- 

 trols, and commence hoisting. Quick reaction 

 to the reduced tension is very important in ob- 

 taining piston corers since the piston action de- 

 pends on stopping the winch with the piston 

 about 1 foot off the bottom. 



Figure L-1',. A spring scale d.vnamometer. 



NOTE: The Sonar Pinger, a bottom signal- 

 ing device, is another method that has proved 

 very satisfactory in deep sea coring. The pinger 

 is attached 20 or 30 meters above the coring de- 

 vice, and the pinger's direct and bottom reflected 

 signals are monitored with a Precision Depth 

 Recorder (PDR) and an oscilloscope to deter- 

 mine when the corer has reached bottom. Chap- 

 ter R, Sonar Pinger, explains the operation. 



L-13 



