Towing, Motion and Stability of Platfornns 



Fig. 8 - Platform on columns stabilized for a 135-foot water 

 depth or for floating semisubmerged in greater depth (South- 

 eastern Drilling Co., Sedco 135) 



If these two criteria are met the platform will be virtually motionless in a 

 vertical direction but must be restrained laterally by an anchoring system. 



A spar platform is simply a long cylinder which is towed horizontally but is 

 erected vertically for working purposes. Its use has been limited to oceano- 

 graphic research, but it could be used for much heavier work. The great verti- 

 cal dimension when upright results in a very long rolling period with good 

 damping. The small water-plane area results in a long heaving period. 



Another special type of rig is the new Production Platform No. 3 for the 

 Freeport Sulphur Company. This is actually a column stabilized platform: how- 

 ever, it is unique in that it rests on the bottom at the beginning of its assignment 

 in 50 feet of water, but it will eventually, due to subsidence of the bottom as the 

 sulphur is mined, find itself no longer on bottom but in water approaching twice 

 this depth. Eight spuds are provided which, once the bottom has started to sub- 

 side, will assist the stability columns in maintaining stability and, at the same 

 time, will prevent lateral shifting. 



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