Macy 



Fig. 1 - Fixed pile supported platform 



that some of these could later be removed by the same method by which they 

 were first placed. 



Single-hull drilling rigs of the ship and barge type are shown in Figs. 2 

 and 3. 



The platform size for a single-hull vessel is limited by stability and struc- 

 tural support considerations. A catamaran offers the possibility of having a 

 very large working platform with normal proportions for the supporting hulls 

 which is beneficial to mobility and maneuverability. Figure 4 shows the 

 E. W. Thornton, one of the few existing catamarans. 



Fixed-height noncolumn stabilized structures are limited to relatively 

 shallow water, and therefore, cannot be considered as true ocean platforms. 

 To submerge such a platform it is necessary to either lower one end to the bot- 

 tom first to provide a stable base while the other end is going down or else pro- 

 vide auxiliary pontoons to maintain stability during sinking. This was the 



448 



