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Re: [PSUBS-MAILIST] Hunley operation & open top ballast tanks



Another thing to consider is if the hull deformed significantly at deeper depths that would change the buoyancy equation.  In my previous posts I have been assuming a rigid hull but we don't know for sure about that.
 
Brian 
----- Original Message -----
From: Brian Cox
Sent: Thursday, May 19, 2005 6:43 AM
Subject: Re: [PSUBS-MAILIST] Hunley operation & open top ballast tanks

Bill,
             Your logic is faulty regarding the buoyancy.  There is no relationship between the amount of pressure inside the hull and the buoyancy, when the cabin in closed to the outside ocean.
 
Brian
----- Original Message -----
From: Akins
Sent: Thursday, May 19, 2005 12:45 AM
Subject: Re: [PSUBS-MAILIST] Hunley operation & open top ballast tanks

Hi Brian.
 
Now Brian, you know I meant that the Hunley could not get to the bottom ON PURPOSE without FIRST using her dive planes. I wasn't talking about an accident like when they sunk.
 
How could the Hunley have submerged without using her dive planes? If we accept that the Hunley had to keep all her interior air and never lost any but only had it pressurized at depth by the inflow of pressurized water into the open top ballast tanks,
 
then how could you fill the ballast tanks without letting air out of them and thus letting air out of the hull? We know they did not do this or else they would have lost air in letting water into the ballast tanks and not had enough air afterwards when
 
they needed to pump out the water.
 
Imagine the Hunley and its ballast tanks are a giant glass. The only difference here is that the Hunley giant glass could stop the amount of water coming into her by closing the valve in her open top ballast tanks when she had all the water inside she needed.
 
If I take a glass and turn it upside down and push it underwater I cannot get more water to go into the glass until I either let air out of the glass, or push it deeper underwater where water pressure will compress the air in the glass and let in more water.
 
That glass would not submerge without me pushing it underwater like a diving plane would a sub in forward motion. But if I push that glass underwater far enough so that the air in the glass is pressurized and does not have enough volume left to float the glass, then the
 
glass becomes neutral or negative. That is what the bow planes allowed the Hunley to do.
 
If we accept that the Hunley never lost any internal air and that she had open top and open to the hull interior ballast tanks, then she would only be able to submerge by using her forward speed and dive planes. Once she was under water, the water pressure would be
 
greater than the  pressure inside the boat and if they opened the
 
ballast tank's inlet valves then water would enter the ballast tanks under pressure from outside.  Then when the volume of air was compressed and lessened inside the Hunley, she would become neutral or negative just like the glass.
 
So the only possibility for the open top ballast tanks, interior atmosphere immediately pressurized upon submergence Hunley, to submerge, would be to force herself under by forward motion and use of her dive planes. Once under and pressurized she could
 
stay under since she is now pressurized and has a lesser volume of air. But she could not have gotten down ON PURPOSE without first using the dive planes and forward motion.
 
Brian if you know how the Hunley submerged without using her forward speed and bow planes, and accepting that she could not lose air from her interior to let in water into the open top ballast tanks, please tell me how she did this?
 
How would you make the open bottom glass go underwater without Letting air out (which they didn't do) or pushing it, like with dive planes?
 
May we please hear from some of our forum experts here on this subject?
 
Kindest Regards,
 
Bill Akins.
 
 
 
 
 
 
----- Original Message -----
From: Brian Cox
Sent: Wednesday, May 18, 2005 9:17 PM
Subject: Re: [PSUBS-MAILIST] Hunley operation & open top ballast tanks

Bill,
 
          Bill wrote....
 
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
 
Ok, but you are at the surface, at 1 ft below the surface you have an additional .45 psi, so yes the sub would be pressurized but only to 16psi or something.  They did not have compressed air, they only had a pump which they could pump the water out of the ballast tanks and there by decreasing they're wieght.  Also they would be increasing the volume of air inside the sub.
 
 The Hunley would have been unable to get to the bottom using her ballast tanks alone.
 
This is not true.  They didn't have any trouble getting to the bottom!   Unfortunately for them.  I think probably one of their problems was not having a pump strong enough to pump against the higher and higher pressure as they went deeper.
 
Regards,
 
Brian
 
----- Original Message -----
From: Akins
Sent: Wednesday, May 18, 2005 1:39 PM
Subject: [PSUBS-MAILIST] Hunley operation & open top ballast tanks

I sent two posts recently about the Hunley, but I didn't see them come back and I don't think they went thru for some reason.
 
One of them I deleted from my sent file before I realized they didn't go thru. The other one I am resending below for Brian and Ian about the
 
Hunleys ballast system and operation.
 
Kindest Regards,
 
Bill Akins.
 
 
 
 
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.