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Hi forum.
I had contacted the Hunley organization and they
told me they would have one of their archaeologists get back with
me.
He did today. From what he says, it seems the
Hunley was technically ambient but not always slightly positively buoyant like
the Holland was.
It seems the Hunley's weight acted as a giant hand
trying to push her under and just a small amount of water let into her ballast
tanks would submerge her.
Here is what he had to say about the Hunley.
Bill Akins.
Dear Sir,
Thanks for your interest in the H.L. Hunley
submarine ....and your questions. Hopefully I can answer
them.
"My information is that
the Hunley had open top (bathtub style) ballast tanks that were open to the hull
interior. My information is that the Hunley did not carry compressed air
tanks."
Yes, the submarine had no compressed air and the
ballast tanks were open to the central crew compartment. However, I should
clarify that the ballast tanks were in the interior of the submarine, separated
from the crew compartment only by a thin bulkhead.
"This would make the Hunley like an upside down
glass trying to submerge without losing any air. The only way the Hunley
could submerge in my mind, would be for the Hunley to use her forward motion and dive planes to force her underwater, is
this correct? Then once underwater the superior water pressure would force
water into the opened valve of the open top ballast tanks and compress the
atmosphere
in the Hunley." Well, not exactly. I think you are looking at
this the wrong way. The Hunley would have been positively buoyant when the
ballast tanks were empty, although just barely. We have a good indication
that she was very easy to swamp - probably as a result of low freeboard and the
fact that she was quite heavy. While she did in fact carry all of her air
with her, it is the water in the ballast tanks that acts as the ballast for the
submarine and determines her buoyancy. Air compresses, water does
not. By opening the valves and allowing water into the ballast tanks, the
sub would become heavy enough to overcome the buoyancy of the air "bubble" and
sink. The air from the ballast tanks would be simply compressed
slightly. In order to surface, the crew would pump out the water by means
of two hand pumps, decreasing the weight and allowing her to rise. With
minimal air pressure, water could always be let into the ballast tanks or pumped
out as needed, but the key factor was always the WEIGHT of the submarine.
In modern submarines, I believe compressed air is used to force the water out of
the ballast tanks, but the air is only functioning like the pumps on the
Hunley. It is still the water or lack thereof in the ballast tanks that
determines whether the sub sinks or rises.
"Also, has anyone done an analysis of how
stable or unstable the Hunley would be if she dropped her keel weight to return to the surface, and were there any indications
of that trying to be done inside the Hunley artifact?"
No and no. I don't think they ever actually
removed the keel weights while under water. I believe it was designed to
be an emergency assent option only. We found no indication that they
attempted to release the keel blocks on her final mission.
I hope this helps answer some of the questions you
had.
Sincerely,
Michael P. Scafuri
********************* Michael P. Scafuri Archaeologist H.L. Hunley Project Warren Lasch Conservation Center P.O. Box 21600 Charleston, SC 29413 |