excellent condition with very little concrete deterioration or rein- 

 forcing steel corrosion after 10 to 40 years service in various seas 

 with different climates. The drydocks, up to 8,500 tons lifting capacity 

 (about 425 x 105 x 48 feet in size) had been constructed by precast 



and in-situ methods of dense, high-strength concrete and had required a 



F £1 



minimum of maintenance^ J 



A precast prestressed concrete floating platform has just been con- 

 structed at Tacoma, Washington. The 68,000-ton displacement vessel, 

 461 x 136 x 57 feet was outfitted as a liquified petroleum gas 

 (LPG) processing and storage facility; it was recently towed to 

 Indonesia and moored in the Java Sea. The platform was segmentally con- 

 structed in a dewatered basin and then floated. The hull, including the 

 precast curved bottom shell elements which weighed 35 tons each, was post- 

 tensioned longitudinally and traversely ,LJ 



The successful emplacement of the Ekofisk concrete oil storage tank 



in the North Sea in 19 73 precipitated a wave of orders for concrete 



[~ 13 1 



gravity (bottom-sitting) structures for offshore oil use.L J Three 



drilling and production platforms were installed in 1975. At least 9 

 more, currently under construction at shallow and deep water sites in 

 Norway, Scotland, Sweden anc * the Netherlands are scheduled for deployment 

 in 19 76 and 1977 in water depths to 510 feet.L 1 J These very large struc- 

 tures are of particular interest to the OTEC program since they are 

 floating during most of their construction and during deployment. They 

 are usually constructed as follows. The base or bottom section is started 

 dry in a dewatered basin near the shoreline. When the walls of 

 the base are sufficiently high the basin is flooded and the bottom section 



13 



