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Hi Bill, I’m talking about adding
more water to the interior (ballast tanks or otherwise) after the sub has
equalized at the surface and the ballast tanks have filled up to their “natural
surface level”, probably only partially flooded, and only then after the tanks have
been sealed off at the bottom. I assumed that since the top of
the tanks were open to the interior and they adjusted ballast by pumping water
out, they must have had a way to seal off the bottom of the tanks, otherwise
more water would come into the tank as they tried to pump it out. With the bottom of the tanks totally
closed off, they then could take on more water by pumping it in under pressure.
This would slightly compress the air inside, decrease the interior volume, add
weight, and decrease buoyancy. Even more basic a design would be
to have enough weight in the sub that once the ballast tanks are opened, weight alone pushes it deep enough to admit
enough water and displace enough interior volume to become negative. I think you could demonstrate it easily
enough with a pipe that is designed with enough weight that it “barely” floats
at the surface. Adjusted right,
almost any amount of water forced inside would sink it. I would assume that the designers
probably wanted good surface flotation with the ballast tanks full of air,
barely float when the tanks were opened at the bottom and admitted whatever
amount of water would enter, and submerge when the tanks were sealed off at the
bottom and enough water was pumped in to make it negative. Granted, it could be done much easier
by pumping air in or out but my thoughts were directed at the original line of
questions that started with no bubble trail leaving the sub for submerging or
surfacing. A pretty novel idea for
a submarine in this period if it holds up. Sorry for the long explanation. Thanks for the Reply. Sincerely, Cliff -----Original
Message----- Hi
Cliff. If
they pumped water from the (open top and open to the hull interior) ballast
tanks into the dry part of the hull or another container within the hull, it
would be the same as letting the water sit right in the open top ballast tanks.
The volume taken up by the uncompressable
water would be the same. The only effect of your suggestion would possibly be
instability caused by not having the water weight in the proper placement for
trim fore and aft in the sub. You
are correct Cliff about them not knowing about dive tables back then.
But it MAY be possible they could have suffered from
decompression sickness before they asphyxiated. In the historical records as
well as the film, it shows the Hunley crew sitting on the bottom
until their lungs could no longer take it and they accended. They sat down
there for hours. If you stayed that long using scuba you would definately be
over your no decompression time limit. The only thing that would make a
difference here is that the Hunley crew
were not breathing or surrounded by a HIGHLY pressurized atmosphere. Also
they were rebreathing stale air and not fresh compressed air. This may have
made a difference as well. Not being a barometric chamber expert or gas
toxicologist I cannot say how long they
could have lasted sitting on the bottom or whether they would have definately
suffered from decompression sickness before they ran out of air and died. That
is an interesting question, and one best answered by the two expert professions
above. Kindest
Regards, Bill
Akins. -----
Original Message -----
Sent: Thursday, May
19, 2005 10:10 AM Subject:
[PSUBS-MAILIST] Hunley ballast I haven’t had time to do much research on the
Hunley but a thought crossed my mind that might help. If they could pump water out of the ballast tanks, could
they pump water into the main compartment or some other type of reservoir
inside the sub? I think I remember
somebody mentioning a bellows type of pump and I would think it could handle
back and forward pressures similar to todays hand bilge pumps. If it could pump against another 5 or 6
pounds of pressure, this would enable them to get down a few more feet with
minimal increase in the cabin pressure.
Don’t know the overall weight and displacement of the sub, but maybe a
few additional feet would get them over the positive hump. Additionally, I don’t think they were too
familiar with dive tables back then (lol). In any event, being unable to use the snorckel suggests that
they didn’t want to release pressurized air from the cabin while
submerged. That limits them to the
air supply that they had when they submerged. With a crew of 8 (?), I think they would have asphyxiated
before suffering from decompression problems. Best Regards, Cliff |