bar at the front of the meter, and insert the 

 worm gear end of the impeller shaft through the 

 hole in the gear box. Then, engage the impeller 

 shaft in the forward bearing bar and lock the 

 bar in place. The impeller is vei-y delicate; 

 therefore, it must be handled with care. 



LOWERING WIRE- 



1 



IMPELLER 

 SHAFT 



Figure M-5. Trigger mechanism Ekman current meter. 



St«p 3. Depress the catch located in front of 

 the compass box, and remove the compass box 

 and compass-ball receptacle. 



Step 4. Pry off the compass-box cover with 

 small screwdriver, and set the compass needle 

 on the pivot point in the compass box. Care 

 should be exercised in handling the meter after 

 this step since the compass needle again could 

 be jarred off of the pivot point by an extremely 

 sharp blow or jolt. 



Step 5. Replace the compass-box cover with 

 the countersunk center hole up and the small lug 

 on the box in the small notch on cover. 



Step 6. Replace compass-box and compass- 

 ball receptacle; close the shutters and lock by 

 engaging arm (C) ; then, fill the reservoir (D) 

 with bronze balls, using the filling tube. 



Step 7. Secure the meter to the lowering wire 

 by tightening the four-screw wire clamp with 

 a screwdriver. 



M-9 Operating the Ekman Current 

 Meter. — Ekman current meter operations are 

 recorded in record of current observations for 

 Ekman current meter (fig. M-6) . 



M-4 



Step 1. Record: Current station No., Date, 

 General locality, Location of station. Latitude, 

 Longitude, and other items in the heading of 

 the data record. 



Step 2. Set the meter trigger mechanism by 

 compressing the two parts of arm (E) , drawing 

 the arm toward tlie vane, and depressing the 

 long end of arm (F) until it rests against the 

 trigger mechanism arm (A). 



Step 3. Make sure that impeller is locked in 

 place, record initial meter reading (upper dial 

 to 100; lower dial to 4000), then lower the 

 meter. 



Step 4. When meter is lowered to the desired 

 depth, record depth of observation from meter- 

 wheel reading, taking into consideration any 

 wire angle greater than 5°. 



Step 5. Attach a messenger to the wire; re- 

 lease it ; and record local time. This messenger 

 open the shutters and unlocks the impeller. 



Step 6. After a definite interval of time 

 (usually 10 minutes) , attach a second messenger 

 to the wire and release it. Record this interval 

 of time in Length of Observation column. This 

 messenger stops the impeller. 



Step 7. After permitting sufficient time for 

 the second messenger to reach the meter, allow- 

 ing 200 meters per minute, hoist the meter to 

 the surface, bring it aboard, and record the 

 final meter reading. Note that dials rotate in 

 counterclockwise direction. The upper jDointer 

 makes one revokition for each hundred revolu- 

 tions of the impeller; the lower pointer makes 

 one revolution for each 4,000 revolutions of the 

 impeller. Care must be taken to keep the meter 

 in a vertical position until the compass-ball 

 receptacle is removed. 



Because some Ekman current meters in use 

 may have reverse-pitch impellers, the direction 

 mechanism of each meter should be checked out 

 before the meter is placed in operation. To do 

 this, revolve the impeller by hand imtil several 

 pellets have dropped into the compass-ball 

 receptacle. Tlien establish the direction toward 

 which a current would be flowing to turn the 

 impeller, using the impeller pitch, the heading 

 of the meter, and the pellets in the compass-ball 

 receptacle. 



M-10 Computing the Current Direction 

 and Velocity. — Current direction and velocity 

 computations are made on the record of current 

 observations (fig. M-G). 



Step 1. Remove the compass-ball receptacle, 

 and place it in the graduated-reading frame 

 with the red comi^artment aligned with zero; 

 then, count the number of bronze balls in each 

 compartment, and record the number and di- 

 rection in the Distrihution of Pellets column. 

 Three pellets for each 100 revolutions of the 

 impeller will be dropjsed in the compass-ball 

 receptacle. 



Change 1—1970 



