For Brian and Ian..
The Hunley ballast system is interesting to
me also.
It of course would depend on how much air
the tanks compressed and how long you were exposed to it whether or not
you would need decompression tables. I'm no decompression/barometric
chamber expert, but if I was going to operate a replica sub
with open to the interior ballast tanks
like that, I would have someone determine what the air pressure in the
hull would be when filling the tanks to different levels, what effect
that pressure would have on my body and for how long I could
undergo that pressure without
having to decompress. I do think it would be prudent to measure this
beforehand rather than possibly making a decompression mistake. That's a
bit like saying..."I'm only scubadiving one more atmosphere deep than
the surface and I don't need to worry, it's not that
important".
But it is. Yes you can scuba to 2
atmospheres (33ft) quite a long time without having to decompress,
but if you stay past the no decompression time at that depth, you start
to build up nitrogen in your blood and if you overstay too long you can
die. So it is something
to worry about anytime the air is
pressurized. You should always know your safety limit time for a specifc
air pressure your body is under.
I don't know of any other sub that
functions like the Hunley's open top to the hull interior ballast tanks.
Might be others, I just don't know.
Brian, you said...."Once you are negitive
or neutral bouyant then valves would be closed and you would maintain 1
atm inside the sub."
This could not be. If you were negative in
the Hunley, then that would mean your tanks had enough water in them in
order to make you negative, which compressed the air in the sub making
it pressurized and therefore you could not be 1 atm inside the
sub.
If you were neutral you would still be
pressurized ambiently because if you were neutral and just hanging in
the water, that is because the pressure inside the sub is the same
pressure as outside the sub. Since you are at depth and pressure is
exerted
upon the hull, in order to be neutral your
air pressure has to be pressurized inside to the same thing which would
be over 1 atmosphere, if you were at any depth of consequence at all.
The Hunley had to be ambient. There
are only two possibilities.
1. the Hunley had crude compressed air
tanks scenario.
This means if she had compressed air tanks
onboard to pressurize the cabin to blow water out of the tanks, then she
would be ambient since her ballast tanks are open to the hull interior
and unable to expell that air pressure until she surfaced.
2. The Hunley had no compressed air tanks
and relied only on her original supply of air from the surface before
she dived.
If the Hunley had no compressed air
tanks, she relied completely on her orignal volume of air from when
she was at the surface and would never lose this air. At
depth the volume of air in the hull would
be compressed by water in the ballast tanks and she would
not be as buoyant. This mean that just like
the later Holland, the Hunley could not
submerge without forward motion and utilizing their diving planes which
forced them under. In the Holland's case she was one atmosphere and would
simply surface if not kept at forward
motion and her dive planes were
the only
thing keeping her under. The Holland's ballast tanks were seperate from
the hull's interior though, unlike the Hunley. That is correct, the
Holland would automatically accend to the surface if not kept at
forward motion.
The Holland was made this way for safety so
she would not get stuck on the bottom theoretically. Think about it. If
the Hunley kept all her original air but it just became pressurized, how
did it become pressurized? Without losing
any air for water to come into the
ballast tanks, the only way that water
could enter the ballast tanks were if it were forced into them under
water pressure at depth. Since you could not dive only using the ballast
tanks because of this, you would have to
dive using your forward motion and dive planes to
keep you under until the water pressure
increased and started filling up the ballast tanks with water which
would pressurize the original air in the entire hull and make you
ambient.
When I watched the movie "The Hunley" it
showed them testing their air starvation endurance by sitting on the
bottom. The Hunley would have been unable to get to the bottom using her
ballast tanks alone. She would have to had forward motion and using
her
dive planes went under with her ballast
tank valves open and when the water pressure increased it would have
filled the open top ballast tanks and pressurized the interior and when
the tanks were filled enough to make the Hunley negative, she would sit
on the bottom.
But she could never have gotten there
without forward motion and use of the dive planes.
See what your teaching did Carsten? By you
explaining to me that once the hull is ambient, unless the air is
compressed and expelled from the hull, you stay ambient until surfaced.
I based my whole above hypothosis on that.
By that one teaching Carsten changed how I
think about buoyancy. See the effect of a teacher and one helpful
lesson? Amazing isn't it.
Now in case I missed something and I'm
wrong I can blame it on Carsten. Ha!
Kindest Regards,
Bill Akins.