SURVEY DESIGN 



Station Locations 



Three anchor stations, designated A, B, and C (Figure 1), were 

 occupied for consecutive 25-hour periods. Stations A and B were lo- 

 cated on the southern periphery of the Bank, and Station C vas lo- 

 cated near its geometric center. Supplementary current information 

 was acquired with a self-contained monitoring buoy, which functioned 

 autonomously through the period of the survey (I-I5 August). Sta- 

 tion positions relative to ARGUS ISLAND, located one mile from the 

 southern edge of the Bank, are as follows: 



Bearing (°TJ 

 St ation Range (yd) From Tower 



Anchor Station A 



2,000 



135 



Anchor Station B 



2,000 



270 



Anchor Station C 



3^000 



020 



Current Buoy 



1,000 



135 



Instrumentat ion 







Low-velocity Roberts current meters (Figure 3) were utilized 

 for all current measurements except those obtained by the current- 

 monitoring buoy» Modifications of the original Roberts radio current 

 meter, including larger fins and impeller blades, were made by the U. S, 

 Coast and Geodetic Survey and have been incorporated in the low-veloc- 

 ity instrument. These changes render the meter more sensitive to low- 

 velocity currents by lowering the speed threshold to 0,1 knot. Accu- 

 racy of the instrument is evaluated at +_0.1 knot and 4_10 degrees. An 

 average error of +5 degrees is somewhat more representative of the di- 

 rectional' accuracy, of the instrument, 



Over-the-side suspension and electrical linkage of the current 

 meter were accomplished with a series 60O electronic bathythermograph 

 hoist (Figure ^) which considerably facilitated positioning of the 

 instrument at desired depths, 



Tbe buoyed current meter system, designed and built by the Bfydro- 

 graphic Office, was tested during the period of the survey. This sys- 

 tem incorporates a Model CM-3 Japanese current meter suspended from a 

 subsurface pressure-resistant float, as shown in Figure 5«> A small, 

 lighted marker buoy was attached by a short length of line to the main 

 float for the purpose of locating and retrieving the buoy system. 



Readout equipment associated with the Japanese current meter was 

 arranged within the subsxirface float as shown in Figure 6, so that 

 dial readings could be automatically recorded on l6mm, photographic 

 film. An electric-motor-driven cam periodically activated a flash 

 camera which photographed temperature, current speed and direction, 

 and clock dials (Figure 7 )• Modification of the original readout 



