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

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.