Re: [PSUBS-MAILIST] Buoyancy and bladders

["Paul Kreemer" <paulkreemer@gmail.com>]

Just had to post agreement to your description Gene.  To list off the key points I see:

*  The bladder/internal tank system is closed, so no change of weight for the sub.

*  The displacement of the sub changes during pumping as the bladder inflates or deflates.

*  The choice of incompressible liquids in the system doesn't affect the displacement change. 

*  The buoyancy change for the sub is equal to the volume of ocean displaced by the bladder volume change.

To apply this with an example: 
Assume a sub in seawater with a five gallon internal tank full of fresh water, and an empty external bladder.
Pumping all five gallons (of fresh water) into the bladder would give a buoyancy change equal to the weight of five gallons of seawater.  ( 5 gal * 
8.6 lb/gal = 43 lb )



Apologies for beating a dead horse-
Paul

On 12/6/06, HUNTR2@aol.com < HUNTR2@aol.com> wrote:

In a message dated 12/6/2006 4:26:36 A.M. Pacific Standard Time, vbra676539@aol.com writes:

The oil inside is transferable payload if you will, and it is transferred payload outside. It displaces whatever volume of water there is to match the amount you pumped out there. Being lighter, it wants to lift. And being hooked to the sub in a bag, that lift is imparted to the vehicle--simple. However, it only gives you a little over 1 pound of lift per gallon in seawater. In comparison, that same gallon of seawater weighs 8 pounds and if you pumped IT overboard, or blew it from a hard tank, then (with the same effort) you'd have 8 pounds less weight aboard without changing volume, thus getting lighter! quicker, cheaper, easier and more efficiently. Thus the question, why use oil?

Vance

Hi Vance. 

There is some confusion here, maybe on my part....  The volume of oil/water or whatever being pumped to the outside of the sub INCREASES buoyancy because it's volume and weight inside the sub is replaced with air, which is much lighter than water or oil.  So pumping seawater outside gives you increased buoyancy on the sub by the same weight of the water pumped out.  Makes NO difference if it is pumped into the blue abyss or a bladder of some sort, the sub will increase in floatation.  You may call it getting lighter... another way of saying not as heavy.  Are you really getting rid of weight or taking on more empty space?    Oil pumped out will accomplish the same thing provided it IS captured in a bladder.  You still increase the airspace inside, thus floatation.  The internal volume change is the same weather oil or water is pumped out.  Pumping oil out and NOT trapping it in a bladder will not cause as much increase in buoyancy because you are not transferring as much weight-per-volume outside.  If you trap the oil in a bladder, then it is the same as pumping the same amount of seawater overboard, because the lesser weight of the oil transferred is made up by the added floatation of the oil trapped in the bladder.  Clear as mud?

 

A bladder with air will certainly increase buoyancy by the same amount of the seawater it replaces.  Still is not a good idea because the bladder, by definition, is ambient, and with air, will be vary, depending on depth, making neutral buoyancy very difficult.