scientists analyzed high-resolution seismic profiles of the Gulf of Mex- 

 ico provided by oil and oil-service companies in order to identify, 

 classify, and map a variety of features indicative of sediment instability 

 and movement. The results of this work have provided the basis for con- 

 tinuing studies of sediments in the Gulf of Mexico and on the Atlantic 

 Outer Continental Shelf. 



Although a knowledge of environmental conditions is important to 

 undersea operations, the success of these operations must ultimately de- 

 pend on the development and improvement of materials, equipment, 

 and instruments for undersea use as well as on the sound planning of the 

 operations themselves. The development of undersea technology is sup- 

 ported largely by the USN. Coordination of the use of submersibles and 

 habitats by the civil Federal agencies is the responsibility of the National 

 Oceanic and Atmospheric Administration (NOAA). 



NEW MATERIALS AND EQUIPMENT 



As vehicles are designed for deeper and deeper ocean waters, the 

 thickness and the corresponding weight of the pressure hull must be in- 

 creased. This increase in weight results in a significant loss of buoyancy. 

 If the vehicle is to carry out its assigned tasks, supplementary buoyancy 

 must be provided. A number of materials and systems have been in- 

 vestigated to provide supplementary buoyancy, but. because of its ease 

 of handling, safety, and fail-safe characteristics under pressure, syntac- 

 tic foam was selected. 



Syntactic foam is composed of hollow microspheres embedded in an 

 epoxy matrix. The diameter of these microspheres is on the order of 10 

 to 150 microns. In order to produce blocks of minimum density, a blend 

 of two distributions of microspheres is used. This blend of a component 

 containing small microspheres with a component containing larger 

 microspheres produces a binary mixture that optimizes the volume oc- 

 cupied by the microspheres in the finished product. Using binary mix- 

 tures, the volume of a syntactic foam block occupied by microspheres is 

 characteristically 72 to 76 percent, depending on the fabrication pro- 

 cedure. 



The finished product is made by either the vacuum impregnation of a 

 prepacked column of microspheres or by mixing the microspheres 

 directly with the resin under vacuum conditions and then curing the 

 resin component. The strength of the final product depends on the type 

 of resin employed, the percentage of microspheres present, and the den- 

 sity of the microsphere component. The density of syntactic foam for 

 use at depths of 20,000 feet has now been reduced from 42 to 34 pounds 

 per cubic foot. This increase in buoyancy, because of the reduction in 

 space required for foam, has resulted in significant savings in vehicle 



62 



