Considerable effort is being expended by 

 both government and industry to decrease 

 the foam's density and, correspondingly, its 

 cost. Present efforts at NSRDC are aimed at 

 developing a 34-pcf syntactic foam for depths 

 of 20,000 feet (8). Both the DSRV's and DEEP 

 QUEST employ syntactic foam of 36-pcf us- 

 ing glass microspheres. Standard 42- to 44- 

 pound foams cost in the neighborhood of $10 

 to $15/pound; 34-pound foam is projected to 

 be some $40/pound in orders of 40,000 

 pounds. An indication of the expense in- 

 volved is gained by considering that DS- 

 20000 would carry some 13,060 pounds of 42- 

 pound syntactic foam. 



According to Rosenberg (7) a 30-pound 

 foam for 20,000 feet should be possible, but 

 considerable development in the glass mi- 



crosphere system is required before this goal 

 can be realized. Owing to its wide application 

 by the marine community — not only in sub- 

 mersibles but in salvage and other areas as 

 well — syntactic foam appears as promising 

 today as did acrylic plastic in its infancy. 



Hard Tanks: 



Six submersibles can be identified that use 

 pressure-resistant tanks as a means of at- 

 taining positive or negative buoyancy. Three 

 of these (SP-3000, DEEP JEEP, DS-2000) 

 use pressure-resistant tanks as a component 

 of a variable ballast system whereby the 

 tank is either blown or flooded and played 

 against an opposing system, such as a small 

 weight drop. 



Fig 6 6 Syntactic Foam blocks cut to serve for stabilization and positive buoyancy on TURTLE- 



297 



