I haven?t been around for a few days but I?ve just checked my mail and I see a wonderful opportunity to ask a question??? It?s not whether a Variable Ballast system is necessary, but what would be the absolute most simple way to build one. Most of the sub?s we?re building can get real close to natural buoyancy by just adding and subtracting been bags full of led shot. The amount of lead shot will be determined in a few short trips and after that It?s easy to calculate any differences. This is a standard procedure and is about as dirt simple as it can get. But it would be a true convenience if a submarine had a small amount of Variable Ballast. My question to all is: What would be the simplest way to build a Variable Ballast system??? Like I said. I haven?t been around for a few days so I?m presuming that this is what all the VBT?s are about. Most people here are not buliding ABS classed boats...just really cool toys