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.