Re: [PSUBS-MAILIST] Response from Hunley archaeologist.

[irox <irox@ix.netcom.com>]

I still don't see any reason that the Hunley is ambient.  If it was ambient it couldn't
dive without pressure compensation, this does not appear to the the case.

Unless some piece of information is missing, the Hunley is 1ATM.  The crew where
always subjected to surface pressure (give or take the very small amount of
pressure increase from the ballast tanks venting into the cabin).  Once submerged,
it doesn't matter what depth the Hunley is at, the crew will be under the same
pressure, if it was ambient, the pressure the crew would be experiencing would
be the same as the external water pressure.

If somebody can supply my the internal volume of the Hunley and the volume of
water used to dive, I will calculate the internal pressure after diving.

Ian.

-----Original Message-----
From: Akins <lakins1@tampabay.rr.com>
Sent: Jun 9, 2005 3:00 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Response from Hunley archaeologist. 

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




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