Current station No.: S Date: //July iHf 



General locality: R4/V/^yiA C^UfKL (PAO) Water Depth: ZOmcZe. 



Location of station; Mag. Variation; U~ ^ 

 Latitude: 03 "SO-yS Longitude: 79 3/. ^f 



Position angles at station occupied : [ K 3 a d ^ ) 

 True bearings of reference objects: 



Figure M-6. Record of current observations for Ekmau current meiter. (PENiCJ NHO 3167/46) 



Step 2. Determine the current direction by a 

 system of weighted averages. For example: 



Number of pellets 

 3 

 5 

 4 



7 



Compartment 

 31 

 32 

 33 

 34 



Direction 

 310° 

 320° 

 330° 

 340° 



Total 19 



6230 

 19 



930 

 1600 

 1320 

 2380 



6230 



= 328° Current direction (magnetic) 



Step 3. Obtain true direction by correcting 

 magnetic direction by magnetic variation. 

 Compasses w ith bronze-ball ti'ough on the 

 ( black; ) south-seeking end of the compass 

 produce direction toward which the current is 

 flowing. The ships hull may cause compass 

 deviation. 



Step 4. Subtract the final meter reading 

 from the initial meter reading, and enter the 

 difference in Diff. cohunn. 



Step 5. Compute current velocity by the 

 following equation : 



Current velocity in knots = 0.010 + 0.012 



Diff. 



e.g. 0.736 = 0.010-f0.012^ 



Step 6. Round current velocity to lOths and 

 enter in Velocity column. 



M-11 Maintenance of Ekman Current 

 Meter. — The Ekman current meter is a delicate 

 instrument, and it requires careful handling. 

 After each current-measurement operation, 

 rinse the meter with fresli water and lightly oil 

 all moving parts. 



M-12 The Roberts Radio Current Meter.— 



The Roberts radio current meter is an instru- 

 nient designed to measure current speed and 

 direction. As the word "radio" in its name de- 

 scription implies, this meter was designed to be 

 used as a part of a current-measuring system 

 that transmits current data to the observer by 

 radio. When the meter and the system of radio 

 transmission and remote monitoring of the cur- 

 Change 1—1970 



Length of observation in minutes 



rent data were developed by Captain Elliot B. 

 Roberts of the Coast and Geodetic Survey, they 

 were a marked improvement over the other 

 methods of current measurements in use at that 

 time, and the Roberts radio current meter has 

 been used successfully by the Naval Oceano- 

 graphic Office on numerous surveys for over 10 

 years. Recently, however, more sophisticated 

 cuiTent meters have replaced the Roberts radio 

 current meter in most applications, but because 

 the Roberts meter lias been used so extensively 

 in the past and is still being used in some opera- 

 tions, a brief discussion of the meter is 

 presented. 



M-13 Principles of Operation. — Three 

 models of the Roberts radio current meter along 

 with the internal mechanism of a meter are 

 shown in figur^ M-7. The gear mechanism (cut 



M-5 



