BALLASTING SYSTEMS 



At least 13 systems can be identified which 

 are used to provide positive, negative and 

 neutral buoyancy in submersibles. These 

 range from venting and blowing steel tanks 

 to merely hanging a cable on the vehicle and 

 letting it drag along the bottom. Three meth- 

 ods of buoyancy control common to almost 

 half of the past and present submersibles 

 consist of a positively buoyant pressure hull; 

 a main ballast (MBT) system to attain sur- 

 face buoyancy and possibly negative descent 

 buoyancy; and a variable ballast (VBT) sys- 

 tem to attain small changes in buoyancy 

 when submerged. In addition to these three 

 methods there are a number of others de- 

 signed to accomplish the same results but in 

 different ways (Table 6.5). 



One method used to gain negative buoy- 

 ancy is the addition of lead or steel ballast to 

 the vehicle based on post-construction calcu- 

 lations and/or sea trials. Although normally 

 used for minor weight adjustments, such 

 weight may be made jettisonable and thus 

 serves an emergency role. 



Ballasting systems are classified herein as 

 Reversible and Irreversible — the distinction 

 being that reversible systems are capable of 

 providing at least one positive and negative 

 cycle during a dive and Irreversible systems 

 provide only a one-time, one-way function. 

 For example, ascent and descent ballasting 

 systems assist the vehicle to dive and then 

 ascend and, therefore, provide both negative 

 and positive buoyancy. Syntactic foam pro- 

 vides the vehicle with positive buoyancy 

 only. The problem with this classification can 



Fig 6 1 Interior of AUGUSTE PICCARD Overhead rows of cylindrical tanks port and starboard hold a total of 842,5 cubic feet of compressed air for blowing main and variable 



ballast. 



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