the following parts are included in the carrying 

 case : 



1. One tail section or vane. 



2. Two individually calibrated impellers and 

 shafts. 



3. Two compass-ball receptacles. 



4. Two messengers. 



5. One metal container of bronze balls. 



6. One graduated reading frame. 



7. One key for tightening the vane tubes to 

 the body of the meter. 



9-39 Assembling the Ekman Current Me- 

 ter. — The meter is seembled for operation as 

 follows : 



1. The vane, or tail, is attached to the meter 

 by two brass tubes which are secured to the 

 vane with left-hand threads and then fastened 

 to the main body by right-hand imions. The 

 unions are tightened with a special key provided 

 in the case. 



2. The impeller is inserted by releasing a bar 

 at the front of the meter perpendicular to the 

 axis of the shutters. Insert the worm gear end 

 of the impeller shaft tluough the hole in the 

 gear box and secure the bar. The forward bear- 

 ing of the impeller shaft is held by this bar. The 

 impeller is very delicate and has been tested 

 and calibrated; therefore it must be handled 

 with great care. Needless to say, the calibration 

 would be worthless should one of the blades be 

 bent or its axis changed. 



3. To place the compass needle in the com- 

 pass box, the compass-ball receptacle must be 

 removed from the main body of the meter. 

 The compass box then becomes removable by 

 pressing the catch on the bottom of the frame 

 just above and forward of the compass box. 

 Remove the cover and set the compass needle 

 on the pivot point in the box. When replac- 

 ing the cover, the bevel of the slot for prying 

 off the cover should face downward and the 

 small lug on the box should fit into the small 

 notch on the cover. Replace the compass box 

 on the frame, then the compass-ball receptacle. 



4. Attach a 15-pound streamlined lead 

 weight, such as the Columbia type, to the bot- 

 tom of the meter frame. 



5- Fill the reservoir with bronze balls, close 

 the shutters, and lock the impeller. The 

 meter is now ready for operation. 



9-40 Operating the Ekman Current Me- 

 ter. — Tliis meter is a complicated, delicate 

 instrument; therefore, it must be handled care- 

 fully. Check it over carefully before each 

 lowering. All movable parts must be oiled 

 and must work freely. It is necessary that the 

 bronze balls be deposited regularly according 

 to the speed with which the impeller rotates. 



The reservoir of balls should be filled and the 

 compass-ball receptacle empty before each 

 lowering. 



The dial readings must be recorded or the 

 pointers set at zero before lowering. The 

 pointers on the meter dial are adjustable, but 

 as they are held on the shafts by friction, 

 adjustments should be kept to a minimum or 

 they will become worn and loose. A recom- 

 mended method is to set the dials to zero at 

 the beginning of survey operations and record 

 the settings before and after each lowering 

 without further adjustments. This way, the 

 last dial reading of an observation will be the 

 first dial reading of the following lowering. It 

 will be noted that the numbers on the dials 

 are in reverse order to give decreasing readings; 

 thus, the number of shaft revolutions for each 

 lowering may be obtained by subtracting the 

 final from the initial reading. 



9-41 Lowering the Meter and Obtaining 

 the Current Data. — The meter may be lowered 

 from either the oceanographic winch or the 

 bathythermograph winch. Successful lower- 

 ings from the latter have been made on Navy 

 surveys. 



After the meter is lowered to the desired 

 depth, a messenger is attached to the wire 

 and released and the time recorded. After a 

 definite time interval, usually 10 minutes, a 

 second messenger is attached to the wire and 

 released. This time is also recorded. The 

 first messenger opens the shutters and unlocks 

 the impeller; the second messenger stops the 

 impeller. After permitting sufficient time for 

 the second messenger to stop the meter, allow- 

 ing 200 meters per minute as the rate of drop 

 for the messengers, the meter is hoisted to the 

 surface and brought aboard. When bringing 

 the meter aboard, care must be taken to keep 

 it in a vertical position until the compass-ball 

 receptacle is removed. Tilting of the meter 

 may cause the balls in the receptacle to transfer 

 from one compartment to another thereby 

 making the lowering worthless. Record the 

 dial readings and time in the Record of Current 

 Observations for Ekman Current Meter 

 PRNC-NHO-1507. 



9-42 Computing the Current Direction. — 

 The compass-ball receptacle containing the 

 bronze balls is removed from the meter and 

 placed in the graduated reading frame. When 

 fitting the receptacle in the graduated frame 

 the red or north compartment of the former is 

 alingned with the graduation of the latter. A 

 ball in any compartment indicates a current 

 having an appro.ximate azimuth corresponding 

 to the number on the frame with a zero added. 



H. O. 607 



93 



