Macy 



Fig. 9 - Platform on columns (note column enlargements) 

 stabilized for a 90-foot water depth or for floating semi- 

 submerged (Odeco, Ocean Queen) 



TOWING RESISTANCE 



Ocean platforms were originally used almost entirely in the Gulf of Mexico; 

 distances between locations were not great, and towing speed was not an impor- 

 tant factor. Today, however, platforms are towed all over the world, and the 

 importance of speed is demonstrated by a recent performance where a 9000- 

 horsepower tug towed a platform having a hexagonal shape hull from Orange, 

 Texas, to Rotterdam, a distance of 5500 nautical miles with a towing time of 58 

 days. The average speed was only 4 knots. It is entirely possible that on cer- 

 tain days the rig lost mileage rather than gained. Many of the hulls of offshore 

 platforms are nothing but rectangular blocks without any shape. Some of these 

 hulls have a slot in them to permit the platform to get away from a finished oil 

 well. Such slots are usually placed aft when towing. 



Figure 16 illustrates most of the hull forms used or proposed. Single hull 

 vessels having the proportions of ships or normal cargo barges have much 

 greater towing speeds, but their deck space, stability, and motion character- 

 istics are not ideal for use as ocean platforms. Floating catamarans are ca- 

 pable of high towing speeds and several of them have been built, one of which 

 is self-propelled, the E. W. Thornton, shown in Fig. 4. 



The type of high load and space capacity platform that has the best working 

 and motion characteristics is the column stabilized platform, which is usually 

 a square, or nearly a square, or a triangular working platform. The first hulls 

 for such column stabilized platforms were of a grid pattern, which was practically 



454 



