The following spare parts are needed to op- 

 erate and maintain the GEK : 

 Spare cable with electrodes. 

 Electronic service kit with a spare set of 

 electron tubes for servicing the amplifier. 

 Spare 1.5-volt dry cells. 

 Spare glass pen with stopper and cleaning 



wire. 

 Bottle of red recorder ink. 

 Spare strin-chart rolls. 

 Instruction manual, "Directions for Speed- 

 omax Type-G Recorders." 

 For normal operations, a medium-size screw- 

 driver and a pen cleaner are all that ordinarily 

 are needed. r^^-rr 



The power required to operate the GEK usu- 

 ally is 110 volts, 60 cycles, AC, with a power 

 consumption under 100 watts. 



M-24 Isolation Transformer.— It is neces- 

 sary to isolate the power with an isolation trans- 

 fonner to block any possible DC leakage that 

 may be present on the lines. The voltage and fre- 

 quency of the input power should be monitored 

 to minimize any variation of timekeeping on 

 the synchronously driven strip chart. Moreover, 

 monitoring assures maintenance of optimum 

 sensitivity of the recorder amplifier, which is 

 slightly sensitive to supply voltage. All com- 

 ponents of the power supply and the instru- 

 ment side of the isolation transformer should 

 be insulated from the ship. 



M-25 Signal Input Leads.— The signal in- 

 put leads connect the overside cable and elec- 

 trodes to the recording potentiometer. They 

 must be shielded and insulated from the ship. 



M-26 Recording Potentiometer.— The po- 

 tentiometer component is a recorder having a 2- 

 second pen movement and i/g-inch-per-minute 

 basic strip-chart speed. The upper part of the 

 instrument scale and the strip chart is calibrated 

 in centimeters per second and the lower part in 

 knots. A set of the ship to port is indicated to the 

 left and starboard set to the right of the instru- 

 ment zero at the center of the scale. 



M-27 The Cable.— The primary function of 

 the cable is to bring aboard a signal from far 

 enough astern to be unaffected by the ship's 

 magnetic field. The clearance between the ship 

 and towpoint should be sufficient to allow the 

 cable to pass clear of the stern even during rapid 

 turns. Aji outhaul to the end of the boom per- 

 mits convenient handling in streaming and re- 

 trieving the cable wlien underway. In streaming 

 the cable, it is necessary to avoid kinks and to 

 keep the cable clear of the screw. The cable may 

 be towed in the ship's wake without adverse ef- 

 fect on the data because the turbulence in the 

 wake usually is too small and too rapid to be re- 



M-20 



solved. Nevertheless, towing from a port or star- 

 board boom is the preferred practice since it 

 causes less damage to the cable. 



M-28 Cable Connections. — Cable connec- 

 tions to the recorder should he, made according 

 to the following convention for the northern 

 magnetic hemisphere : the conductor leading to 

 the more distant electrode is connected to the in- 

 put terminal which is made positive and gives 

 a right-hand deflection of the pen. This con- 

 vention allows the observer facing the recorder 

 to see the i^en on the same side of zero as the di- 

 rection toward which the ship is being set. The 

 connections must be reversed in the southern 

 magnetic hemisphere to have the same conven- 

 tion apply. 



M-29 Electrodes. — The electrodes have been 

 specially lagged in order to withstand repeated 

 changes of salinity and temperature. Allow at 

 least 30 minutes wetting time on deck before the 

 first towing of the electrodes. The electrodes 

 then will require only about 5 to 10 minutes 

 towing before they respond. It is not necessary 

 to rewet the electrodes before additional towing 

 even though they may have been on deck several 

 hours. 



NOTE: Care must be exercised not to in- 

 advertently apply an electric potential to the 

 GEK-towed electrodes, either from an external 

 source such as an olunmeter or from galvanic 

 effects, since the electrodes may become polar- 

 ized and exhibit a pennanent bias potential be- 

 yond the range which the equipment can accom- 

 modate. For this reason, the following precau- 

 tions must be observed : Do not ground the elec- 

 trodes or the towing cables at any point ; do not 

 allow wet electrodes to come into contact with a 

 metal surface, such as the ship's deck, because 

 of galvanic potentials that may be developed; 

 when electrodes are being soaked in salt water 

 on deck prior to or between launchings, be sure 

 that the container holding the salt water is of 

 nonmetallic material (e.g. a plastic or wooden 

 bucket). 



M-30 Operating the GEK Model V.— Opera- 

 tion of the GP]K Model V is carried out in the 

 following manner. 



Step 1. Rig out the boom and stream the elec- 

 trodes. Connect a 10-foot piece of %-inch manila 

 line to the outboard electrode to dampen its os- 

 cillation. 



Step 2. Turn the POWER switch (A) and the 

 PAPER MOTOR switch (B) on the panel of 

 the GEK recorder (fig. M-21) to OFF 

 (DOWN) position. 



Step. ;). Plug in the electrodes at the input 

 terminals, turn on the 110-volt AC power sup- 

 ply, and turn POWER switch (A) to ON 

 position. 



Change 1—1970 



