step 4. Move PAPER MOTOR switch (B) 

 to ON position. 



Step 5. After 1 minute of power-on, tvirn tlie 



^ SEMIAUTOMATIC CURRENT ADJUS- 



' ) TOR (C) clockwise for an instant and repeat 



until the recorder pen does not respond. The 



pen should now rest at zero in the center of the 



chart paper. 



Step 6. Turn the SENSITIVITY CON- 

 TROL knob (D) clockwise all the way, and 

 -X then return it to the point where the pen ceases 



) to quiver. 



Step 7. Set the FILTER TIME CON- 

 STANT switch (E) to the center position 

 RC = RC. 



Step 8. Set the VERTICAL INTENSITY 



knob (F) to the value of the nearest standard 



isodynamic line shown on H.O. Chart No. 1702 



) for the position of the ship at the time of the 



observation. 



Step 9. Set the FILTER SHORTING 

 switch (G) to the center position SUPPRESS 

 WAVE. 



Step 10. Set the FILTER RESISTANCE 

 dial (H) on zero; then, increase the setting until 

 the wave signals are sufficiently suppressed to 

 give a i-eadable trace. Do not suppress the wave 

 signal excessively as this will make the pen 

 response too sluggish. An oscillation \vith a 

 range of about 15 cm. /sec. is best. In rough 

 weather when heavy wave signal suppression is 

 needed and after the ship has completed a turn, 

 ) it is well to examine the wave signal without 



suppression from time to time. To do this, move 

 switch E momentarily to the RC=0 position. 

 In case a capacitor is faulty or the sea is on the 

 beam, the suppressed signal will not coincide 

 with the densest part of the unsuppressed signal. 

 If a change of FILTER RESISTANCE dial 

 (H) has no affect, the asymmetiy is the result of 

 the wave direction. 



Step 11. Adjust the SIGNAL MULTI- 

 PLIER (K factor) dial (I) to increase the 

 amplitude of the input signal to correct for ef- 

 fects of subsurface cuiTents. The correct setting 

 of the dial is determined as a function of the 

 vertical-water- velocity profile. For water deeper 

 than 75 fathoms and where tidal motions are 

 weak, the SIGNAL MULTIPLIER dial should 

 be set at 1.10. At depths of less than 35 fathoms 

 and where tidal currents predominate, the dial 

 should be set at 2.0. Between 75 and 35 fathoms 

 adjust the dial between 1.10 and 2.0. 



Step 12. Before the initial base-coui-se run 

 is begun, set switch (G) to ELEC. SHORT 

 position, and adjust the recorder pen to the in- 

 strument zero point by use of the ELEC. ZERO 

 dial (J). Return switch G to SUPPRESS 

 WAVE position. Onc« the setting is made on 

 ) dial J, it should not be changed during the pe- 



riod of tlie current observation. 



Change 1—1970 



NOTE : In the vicinity of such features as 

 the westerly boundaiy of the Gulf Stream, the 

 changing temperature and salinity may shift 

 the zero point at each crossing. Study the zero- 

 point trends, and if necessary adjust the zero 

 point before the GEK run so that it will shift 

 syimnetrically about the instrument zero \vith 

 each crossing. 



M-31 Maneuvering the Ship for the GEK 

 Observation. — The couree the ship is required 

 to steer for a GP]K observation is determined by 

 the requisites: (a) That potentials must be 

 measured on at least two headings at right 

 angles if possible and (b) that because of 

 electrode polarization, the electrodes must be re- 

 versed end for end for each current fix to de- 

 termine the zero point. This zero point is the 

 average of the two voltages obtained by making 

 a 180° course change. A current fix is accom- 

 plished by executing a steaming pattern as 

 follows (fig. M-22) : 



Step 1. After the electrodes have become 

 thoroughly .soaked and the pen motion has 

 steadied, remain on base course for 4 minutes. 



Step 2. Change course 90° and run for 4 min- 

 utes after the electrodes steady-on the new 

 course. This is the first fix-course. 



Step 3. Change course 180°, turning in the 

 direction of the base course, and run for 4 min- 

 utes after the electrodes steady-on the new 

 course. This is the second fix-course. 



Step 4. Change course 90° and resume the base 

 course. Run for 4 minutes after the electrodes 

 steady-on the base course to obtain the resumed 

 base-course data. 



(I) REMAIN ON BASE-COURSE 

 4 MINUTES 



(2) CHANGE COURSE 90° 

 THIS IS THE 



(3) CHANGE COURSE 180° 



RESUME BASE-COURSE 

 4 MINUTES 



i , (4) CHANGE COURSE 90* 



Figure 31-22. Directions for executing a GEK current 

 fix. 



M-32 Recording the GEK Data.— GEK 



data obtained by executing the current fix are 

 recorded on oceanographic log sheet — GEK 

 (fig M-23), and certain items of the data are 

 annotated on the recorder strip chart (fig. M- 

 24). Print all entries accurately' and neatly. 



Instructions for filling in the log sheet and 

 annotating the recorder chart follow : 



Step 1. On the log sheet and the recorder 

 strip chart, enter the ship's name and number, 



M-21 



