area of the permanent site to elevations of about 50 feet (15 m) below 

 sea level indicated very weak cover, this material was removed subse- 

 quently by dredging. Diver-operated water-jetted probes revealed 1/2 

 (.15 m) to 5 feet (1.5 m) of loose cover at most anchor locations at the 

 permanent site after dredging. No data were obtained prior to anchor 

 installation to indicate the strength of the underlying coral at either 

 site. Consequently, anchor projectiles were prepared in two sizes, the 

 smaller for medium- strength coral and the larger for soft and broken 

 coral to provide flexibility in onsite anchor selection to obtain the 

 desired performance. 



Experience has shown that propellant anchors are more efficient in 

 harder materials, as indicated by Mayo (1973), Smith (1971) and Taylor 

 (1976). Accordingly, the capacity of the larger projectile in an assumed 

 softest credible material was taken as a lower limit to design capacity. 

 Based upon a buoyant density, measured on grab samples of 51 pcf (0.82 

 gm/cm-^) and an assumed friction angle of 30 degrees, this minimum capacity 

 was calculated at 148,000 pounds (660 kN) by the method of Taylor and Lee 

 (1972). 



Four-point spread moorings were required to fit the operational 

 needs for POL offloading at Diego Garcia. In order to provide redundancy 

 and an acceptable factor of safety, a leg configuration employing two 

 anchors and a load equalizer was selected. A chain-load equalizer was 

 selected to make use of the ample chain available onsite. Also, the use 

 of chain precluded the wear and fouling problems that might arise if a 

 wire rope running over a sheave were used instead. The tensions on the 

 two ends of the equalizing chain T 1 and T_ and the tension in the buoy 

 chain T^ are related as 



lnOy^) ^= Try 



T i=r T + T 



B 1 2 



The approximation is good for small angles between the two opposing 

 portions of the equalizer chain. 



Combining to eliminate the smaller chain tension gives 



T„ 



T„ « 



L 2 1 + exp(-iry) 

 The factor of safety (F.S.), in terms of known forces, is then 

 F . S . = H/T 2 - H[1 ^(-iry)] 



