Macy 



Fig. 11 - Platform comprising oil storage tanks with a 

 submersible bottom mat (Chevron Oil Co., S-9Z) 



speed-to-length ratio of long catamaran hulls is very low and results in a low 

 resistance per ton as compared with that of individual footings. 



Figure 17 speaks better than words in describing the vast variation in re- 

 sistance of platform types. It is difficult to obtain a sufficient quantity of good 

 data on towing resistance on some of the unusual forms that are used. This is 

 due to the fact that most model tests are made by the individual companies for 

 their own use, and at the present time such data is regarded as confidential. 



Extreme refinement in hull forms for elevated deck ocean platforms is not 

 justified, because the large platform structure raised on columns high above 

 the hull has wind resistance which is a large component of the total resistance. 

 Furthermore, high freeboard in the hulls of column stabilized platforms is not 

 necessary from a stability standpoint, as the columns provide stability anyway 

 when the hull is being submerged. In addition, the presence of an excess hull 

 volume compared with the column volume results in the center of buoyancy be- 

 ing unfavorably low for stability. Therefore, there is a tendency to keep not 

 only the displacement but the freeboard of the hulls to a minimum. This has a 

 disadvantage in towing in that even moderate waves will wash over the hull and 

 strike the columns, causing a considerable augment in resistance. While most 

 of this is due to the large stability columns, there is considerable effects on 

 the smaller support columns as well. 



456 



