----- Original Message -----
Sent: Monday, January 02, 2006 5:51
AM
Subject: [PSUBS-MAILIST] Compressable
ballast tanks
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.