PIPE 



Figure 3. Spar Coupling 



Virtual Mass 



Two flooded 55 gal drums, which serve as virtual mass, are 

 connected below the spar by a chain. The weight of the 

 releasable ballast and of the array hanging from the bottom of the 

 drums forces them to move vertically with the system almost as well 

 as if they were rigidly fixed to the spar. Swell-surge action 

 during launch and recovery does not allow a rigid connection, al- 

 though that would be the best. Each drum has about 15 1-inch diameter 

 holes punched in the sides near their bottoms, and smaller vent 

 holes in the tops to allow for rapid flooding upon launch. This 

 scheme of captured mass raises the natural period tuning-weight 

 by 1040 lb, yet requires only 100 lb of additional buoyancy to 

 support the drum weight. 



Reserve Buoyancy 



As a backup, in case any part of the buoyancy system fails, a 

 pressure releasable ballast weight was added. This is a 100 lb, 

 cast-iron weight suspended beneath the virtual mass containers by 

 a Benthos Corporation model 1790A-PH pressure-actuated, pelican 

 release. If for some reason the spar sinks, water pressure at 

 approximately 75 m will trip the release and drop the ballast. 

 This additional buoyancy will more than compensate for flooding 

 of a 10 ft length of large spar pipe, flooding of all 30 ft of 

 reduced spar section^ or the complete loss of the top 30 ft of spar, 



172 



