I. IMTRODUCTION 



It is sometimes necessary to install an instrument package in 

 the ocean at a prescribed depth between the surface and the bottaa 

 and to laaintain the location of the package within prescribed limits 

 even in the presence of tidal and other currents. The instrument 

 package is ccsnmonly installed in a buoyant housing (a buoy) tethered 

 to the bottom by means of cables. A high degree of locatlonal 

 stability in the presence of water currents can be obtained by use 

 of three tether lines fastened to three widely spread smchors on 

 the ocean bottom. This type of mounting often presents great diffi- 

 culty and expense in installation, especially at larger depths. An 

 alternate mounting is obtained by use of a single tether line with a 

 buoy of large buoyancy and a very heavy anchor. The high tension in 

 the tether line helps prevent the currents from moving the buoy side- 

 wise. We have found that the latter approach is applicable to a 

 situation where the lateral motion of a subsurface buoy in deep 

 water heid to be limited to ten feet emd subsurface currents were 

 estimated to be 0.2 knot. 



II. EXPERIMENTAL DETERMIMTION OF STABILITY 



In order to accxirately calculate the stability of a buoyant 

 system one must first know the vertical current profile over a 

 given period of time. Since this information was not available 

 in sufficient detail, an experimental approach to the problem 

 was made. A spherical steel buoy, four feet in diameter, was 

 anchored in I9OO ft. of water with I3OO ft. of one-inch diameter 

 nylon line and a 35OO lb. concrete block. The net buoyancy of the 

 sphere was I3OO lbs. A self-contained pinger unit (SCUPU) was 

 attached to the sphere to allow acoustic tracking by the 3-D track- 

 ing range. 



With the SLnchor tied alongside and the sphere streaming aft the 

 support vessel maneuvered up to the release point. On command the 

 emchor was released ajid the SCUPU was tracked as the anchor dragged 

 the buoy along the surface and then down into position. The track- 

 ing data is shown in Fig. 1. Analysis of the buoy track indicates 

 that the anchor stnick the bottom, with the buoy at a depth of 

 530 ft . ,and then slid westward down a steep incline dragging the 

 buoy to a depth of 590 ft. The buoy then slowly stabilized its 

 position above the anchor. 



The SCUPU was tracked continuously for thirty minutes after the 

 buoy was in place to be certain that its position had stabilized. 

 After that a series of twenty readings (I.3I seconds apart) was 

 taken at the end of each five minute interval for a period of k2 

 hours. The variation within each 20 bit grouping was generally 

 three feet or less. The averages of the group taJten in successive 

 five minute intervals occasionally varied by as much as six feet. 



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