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-----
From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Akins
Sent: Friday, May 20, 2005 11:21
AM
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Hunley
ballast
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 -----
To: Personal_Submersibles
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