Bill,
The changes in buoyancy of a scuba tank is negligible for all practical purposes. Remember... the K I S S rule...
Hugo
Hi fellas.
I was thinking about the variation in buoyancy in my aluminum scuba tanks. You know when your tank starts to get low on air how
it becomes more buoyant. A thought struck me about how that might be counteracted that then led to another thought concerning
ballast tanks for a sub. With the scuba tank, I was thinking, what if it had a bottom that moved up and down the length of the tank
like a piston in an engine. As the tank emptied from my breathing, the bottom of the tank would be forced toward the top of the tank
by the water pressure until the remaining pressure in the tank stopped it from moving. In this way the rest of the tank volume would
now be replaced by water and the tank wouldn't get more buoyant as it emptied. Of course you would have to have a very good
foolproof seal. Even perhaps a seal that the tank's internal air pressure would push against to make the seal tightly seal. I wonder
if anyone has ever tried making something like that? That was my first idea. Then that thought made me think about this. On my wetsub
I've been planning to install
6 or 8 inch pipe about 4 feet long on either side for my soft ballast tanks. I had planned to use two scuba tanks
to blow them and the scuba tanks would each be attached to the top of the pipes on either side of the sub providing plenty of air for both
the soft ballast pipes and also for the hard ballast bladders in the bow and stern. What I was thinking about was if I could use the same idea
as with the scuba tank moving bottom on my soft ballast tanks. Suspose I had a piston with a really good seal. Now I'm on the surface
with the soft ballast pipes full volume keeping me up, then I could either crank the piston inward or even use hydraulics to
push the piston inward. That would compress the air in the soft ballast pipe and lower its volume and I would submerge. Then when I wanted to
surface, I could crank the piston out, allowing the air to expand, the volume to increase again, and then I would surface. That way I wouldn't have
to use any air tanks to fill my soft ballast tanks. Sounds like it would work to me but I'd have to make the pipe smooth and have a tight fitting
piston with a really
good seal on it. If the seal ever blew out I could use my hard ballast tanks and my own personal BCD and still get the sub to the
surface and I could also always bail out if I had to. Just a thought about the variable volume scuba tank and soft ballast tanks. What do you
fellows think?
Bill Akins.