CONSTRUCTION AND TESTING 



Plaited nylon line was selected for use in the 

 1970-71 arrays because of its great strength and 

 elasticity, as well as for its ability to stretch 

 and then return to its original length with no 

 loss in strength (Figures 5-6). As a result of its 

 elasticity, nylon is able to absorb the large 

 amounts of energy present during launching and 

 during severe conditions such as storm waves or 

 strong currents (Figure 7). Plaited nylon also 

 resists twisting and kinking, thus eliminating the 

 need for swivels in the mooring line. 



When placed under an initial load, new nylon 

 will be permanently elongated by approximately 

 10% (Figure 4) ; thus each section of nylon line 

 in an array was cut shorter than its designed 

 length. During launching, the new nylon line 

 was placed under tension by the falling anchor 

 and permanently elongated by approximately 

 10%. 



Each piece of nylon line was terminated at 

 both ends with a 3 or 4 tuck eye splice whipped 

 with nylon line or black plastic tape (nylon 

 whipping proved superior to the plastic tape). 

 A steel thimble was used in each eye splice to 

 prevent the nylon line from chafing. The nylon 

 line and eye splices were tested by suspending 

 the anchor from one section. 



Hardware items such as shackles and sling 

 rings were selected so that the ultimate strength 

 of any part was at least five times greater than 

 the maximum tension the array was designed 

 to withstand. Safety marine shackles, locked 

 with cotter pins, were used to join sections to- 

 gether. To reduce corrosion, the cotter pins were 

 only slightly bent after insertion. 



In 1970, two Geodyne Model 102 photo- 

 graphically recording current meters were tested 

 by operating them in a darkroom with the pres- 

 sure cases removed and a test strip of film in the 

 magazine. After it was determined that the 

 meters were functioning and sequencing prop- 

 erly, the meters were reloaded with film and 

 the pressure cases were replaced. 



Two Geodyne ^lodel 850 magnetic tape re- 

 cording current meters were also used in 1970. 

 Four 850 current meters were used in 1971. A 

 characteristic failure of these instruments is for 

 the tape to wind around the capstan drive and 

 stop the recorder. Each of our recorders was 

 carefully tested to insure that the capstan drive 

 functioned properly. Then the current meters 

 were run in the lab for several days with test 

 tapes in the recorders to determine if the tapes 

 advanced pi'operly. ]\Iagna-See fluid was used 

 to insure that data were being recorded on the 

 tape. A new piece of test equipment manufac- 

 tured by Geodyne enabled the Instrument Sec- 

 tion to gi\"e each current meter a comprehensive 

 checkout before it left the lab in 1971. After 

 testing, each meter had a new battery installed. 

 Each battery was checked by placing it imder a 

 100 ohm load and measuring the voltage prior to 

 installation. Before each tape cartridge was in- 

 stalled, it was erased to clear it of any noise 

 which might later interfere with computer proc- 

 essing of the recorded data. Several desiccant 

 bags were placed into each current meter before 

 it was sealed . 



The "O" rings at the top and bottom of the 

 case were removed and replaced with properly 

 greased new ones before the pressure case was 

 placed on the current meter. Care must be taken 

 when placing the pressure case on the current 

 meter to insure that the "O" rings are not pinched 

 or improperly seated, or the meter will flood. 

 Placement of the top "O" ring is especially 

 critical. Once the pressure case was in place, 

 the tie rods were torqued to 10 ft-lbs. The cur- 

 rent meters were then jjressure tested to 200 

 meters by the National Oceanographic Instru- 

 mentation Center. In 1970, the current meters 

 were tested by suspending them in the Anacostia 

 River just below the surface for about 3 hours. 

 In 1971, one of the current meters flooded as a 

 result of an improperly installed top "O" ring 

 which had become pinched between the cap and 



