In the moored mode, the "buoy is limited in travel to its watch circle, or 

 horizontal radius of its mooring line around the anchor. The buoy is moored via 

 a special mooring accumulator obtained from ENDECO and an anchor chain. The accu- 

 mulator consists of an elastic cord encased by braided nylon rope. The accumulator 

 can elongate up to three times its static length before the rope becomes taut. 

 Therefore the abrupt forces acting on a buoy at the end of its line are reduced. In 

 this mode, a ship is also free to perform other activities while collecting wave 

 data. Mooring is limited to relatively shallow water and is not practical in the 

 open ocean. However, DTNSRDC has moored these buoys, in conjunction with other 

 investigators' instruments, in water depths of up to 600 meters. 



In the third mode, the buoy is tethered to the ship using the mooring accu- 

 mulator and any additional line necessary. This method provides for an easy 

 retrieval of the buoy. It is not necessary to maneuver close to the buoy and 

 try to grab its flag line during retrieval. When the seas are rough, this may 

 be the only way of practically deploying the buoy. The ship would not have to 

 track down and maneuver close to the buoy while battling rough weather. 

 However, in this case as well as in more benign conditions, it is desired that 

 the ship try to maintain a slack line between the buoy and ship. 



The three modes of deployment provide some latitude in collecting wave 

 directional data for various conditions. However, it may be necessary to interpret 

 the results to account for mooring or drifting. 



DATA COLLECTION 



When the buoy is deployed, the wave height and direction data are collected 

 via telemetry and onboard solid state memory. An overview of this procedure of 

 data collection is shown in Figure 5« 



The data collected through telemetry is transmitted via FM radio link from 

 the buoy to the receiver onboard the ship. Once the data reaches the receiver, 

 it is output in digital and analog form. The analog data is recorded on analog 

 tape for a backup and in case the user wants to redigitize at different sampling 

 rates or wants to apply analog filters. The receiver also digitizes the data at a 

 rate of one hertz, which is then transferred to floppy disk via a PDP 11/23 mini- 

 computer. An advantage of collecting the data on the computer is that it is then 

 possible to analyze the data in near real time while still on board the ship. 



11 



