Towing, Motion and Stability of Platforms 



T 



Fig. 



2 - Floating ship with center well (Global 

 Marine, Inc., Glomar III) 



common type of offshore drilling platform in the early days but is no longer be- 

 ing built except for relatively shallow water oil storage platforms such as that 

 shown in Fig. 11, a tank-battery platform. 



Jack-up platforms are basically a buoyant hull which is at the same time 

 the working platform. Attached to this hull are legs which are lowered to the 

 bottom until they encounter soil resistance after which jacks on the columns 

 raise the hull out of the water to the desired clearance. The bottoms of the legs 

 may penetrate the soil independently like those of Figs. 5 and 7 or they may be 

 attached to a buoyant or a nonbuoyant hull as shown in Fig. 6. With a lower hull 

 much better soil bearing is obtained, but this is at the expense of additional 

 steel structure. Although a number of accidents have occurred with jack-up 

 platforms, the type is very successful and economical and there are perhaps 

 more platforms of this type in service than any other type. 



Column stabilized barges consist of a hull having several large -diameter 

 columns supporting a fixed platform. These may be submerged by flooding, and 

 the platform will sink vertically either all the way to the bottom or to some in- 

 termediate draft. Once the hull has submerged below the surface, the stability 

 is afforded by the water plane moment of inertia of the stability columns. Such 

 platforms are shown in Figs. 8, 9, 10, and 12. 



Figures 13 and 14 show a small column stabilized platform for oil well serv- 

 icing having hinged stability columns. When the columns are each rotated 90 



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