BUOY ARRAY DESIGN 



All of the taut-line arrays set by the IIPRS 

 in 1970 and 1971 used surface flotation which was 

 on hand at CGOU. The floats used were Geodyne 

 Model A-92 toroidal instrument buoys (Figure 

 2). A Geodyne ^Model A-93 tripod tower on 

 each buoy sui:)ported a pair of wire mesh, life- 

 boat radar reflectors and a Geodyne IModel 180 

 Xenon light. A rigid tripod bridle, Geodyne 

 :Model B-301, attached to the bottom of the to- 

 roid, supi^orted the subsurface portion of tlie 

 array. 



FiGUBE 2. Surface buoy, Geodyne Model A-92. 



The use of surface flotation introduces major 

 problems which can eft'ect the survivability and 

 reliability of taut-line arrays. 



• Surface floats are susceptible to collisions 

 with ships, fishing trawlers and seiners, ice- 

 bergs, and, in some locations, sea ice. 



• Surface floats with radar reflectors and 

 lights are highly visible, and are, there- 

 fore, siibject to well-intentioned recovery or 

 theft. 



• The use of surface floats requires a very 

 accurate determination of water depth at the 

 mooring site. 



If the water depth were not accurately known 

 and the array were set in water exceeding the 

 design depth, heavy seas, large tidal rises, or 

 strong currents could cause the anchor to be lifted 

 ofl: the bottom since the i-eserve buoyancy of the 

 surface float exceeded the weight of the anchor. 

 If the anchor were carried into deep enough 

 water, the entire array would be free to drift and 

 could be lost. If however, the array were set in 

 too shallow a depth of water, the mooring line 

 could go slack and kink, or the current meters 

 could be inclined in excess of 15° from the 

 vertical by the current, making the readings 

 unreliable. 



To determine water depth accurately at the 

 mooring site, a Salinity/Temperature/Depth Sys- 

 tem (STD) cast was taken and the sound velocity 

 was computed at various depths. A weighted 

 mean sound velocity, R, was then calculated. 

 The depth at the mooring site, as indicated by the 

 vessel's fathometer, was noted. The time (T) 

 required for the fathometer signal to reach bot- 

 tom and return was determined from the re- 

 lationship : 



Z = -^ (1) 



where: Z = fathometer indicated depth, ft. 



11=4800 ft/sec (sound velocity for 



which the fathometer 



was calibrated) 



T=time, sec 



A more accurate value of Z was then calculated by 



substituting the values of R and T into equation 



Mooring Line Tension Calculations 



In 1971, the taut-line arrays were designed 

 to satisfy the following requirements. 



• Mooring line tension must not exceed 15% 

 of the breaking strength of the line. 



