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Re: [PSUBS-MAILIST] Forces of Nature

True If the tank/ cabin is open to the water and no further is added to keep the same displacement and keep the air at ambient pressure.
A point ive never really considered though is that say you have a dry ambient design obviously air is being added to keep the inside of the cabin slightly above or at ambient pressure and since its dry also at the same displacement. however since you are increasing the pressure therefore density of the gas inside the cabin this would surely affect the overall weight slightly, much in the way a full steel scuba tank starts as negatively bouyant but as it is emptied throughout a dive progressively becomes more nuetrally bouyant as the gas inside becomes less dense.
however since the pressure inside an ambient design is very unlikely be very great ( unless your a loon building a saturation bell) do you think that any weight/bouancy change would be significant considering also that whilst you are increasing the density oa gas inside the cabin you are also decreasing the density of gas inside the supply tanks.
whoops i think ive just answered my own question and in fact overall i guess the whole system will just become slightly more bouyant due to the loss of exhaust gasses. 

Let me know if you think that sounds about right,

Cheers,

Dan

From: "Akins" <lakins1@tampabay.rr.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] Forces of Nature
Date: Wed, 9 Nov 2005 19:57:46 -0500
Water, thru ambient water pressure, compressing the air inside the cabin or tank, changes the air displacement if you do not 

add any air to replace the compressed air.

Bill.




  ----- Original Message -----
  From: Daniel Edwards
  To: personal_submersibles@psubs.org
  Sent: Wednesday, November 09, 2005 6:33 AM
  Subject: Re: [PSUBS-MAILIST] Forces of Nature


  the bouancy should not change if the exact shape of the vessel does not
change because it still displaces the same amount of water which does not become denser due to compression. therefore bounancy is about displacement 
  not wether the air inside is compressed if you see what imean


  >From: "Akins" <lakins1@tampabay.rr.com>
  >Reply-To: personal_submersibles@psubs.org
  >To: <personal_submersibles@psubs.org>
  >Subject: Re: [PSUBS-MAILIST] Forces of Nature
  >Date: Wed, 9 Nov 2005 00:59:57 -0500
  >
  >Hi Joe.
  >
>Not sure if I am reading your questions correctly, but I will try to help 
  >and hopefully be corect for what I think you are asking.
  >
>Remember that 1 atm is the air pressure at the surface and is the 14.7 psi 
  >we have pressing against our bodies (GENERALLY speaking)  ALL the time.
  >
  >If you want to submerge something to say 33 feet, that would be 2 atm.
  >Remember to count the
  >
>single atmosphere we already have pressing on us all the time. So 33 ft is 
  >2 atm, 66 ft is 3 atm, etc.
  >
>You asked.....#1 One submerges a bubble of air (enclosed in any material) >and open to ambient pressure to 1atm . Equal forces of pressure are applied >to either side of the material. I assume that the lifting force of the air 
  >in pounds of buoyancy is not cancelled out by the equalization of that
>pressure. That the material is subjected to a stress in psi equal to that >force. Then if one were to apply an opposing force ,as in ballast, that the >material is then subjected to both forces. Is this a correct assumption? 
  >
>The first part of your question I assume you mean't submerging a bubble of 
  >air at ambient pressure at greater than 1 atm.
  >
  >The second part of your question states about applying equal force to
  >either side of the material. I assume you mean the water pressure force
  >
  >going into the main soft ballast tanks or even part of the subs ambient
  >hull (depending on design) and then having equal force applied by
  >
  >releasing air into the same space and therefore the material (hull or
>tanks) has equal force applied onto it from both sides which cancels each 
  >other's force
  >
  >out, remembering of course that there has to be a slight pressure
>difference inside, in that the inside air pressure force holding out the 
  >water has
  >
  >to be slightly greater than the water's pressure trying to get in. That
>sounds correct if that is what you mean't. I wasn't quite sure what your 
  >third part of the question mean't
  >
>when you asked whether the lifting force of the air was not cancelled out >by the equalization of that pressure. Are you asking if by pressurizing the 
  >vessel, (material, bubble, whatever) if
  >
>the lifting force of the air is decreased by being compressed against the >outside water pressure? If that is what you were asking, I am not the best 
  >to answer this, but I do know that the deeper
  >
  >you go and the more you compress air, it does have an effect on its
  >buoyancy I believe. I'll leave that one for someone a bit more
  >knowledgeable in math to compute buoyancy loss due to air molecule
  >
>compression. But I hope I helped you some, and remember we are always at 
  >approximately 1 atm all the time.
  >
  >Bill.
  >
  >
  >
  >   ----- Original Message -----
  >   From: Joseph Perkel
  >   To: personal_submersibles@psubs.org
  >   Sent: Tuesday, November 08, 2005 12:15 PM
  >   Subject: [PSUBS-MAILIST] Forces of Nature
  >
  >
  >
> My learning curve is flattened again, too many distractions, Please help 
  >me with some basics here.
  >
  >
> #1 One submerges a bubble of air (enclosed in any material) and open to >ambient pressure to 1atm . Equal forces of pressure are applied to either >side of the material. I assume that the lifting force of the air in pounds >of buoyancy is not cancelled out by the equalization of that pressure. That >the material is subjected to a stress in psi equal to that force. Then if >one were to apply an opposing force ,as in ballast, that the material is 
  >then subjected to both forces. Is this a correct assumption?
  >
  >   #2 One submerges a piece of marine ply to one atm. Is the cellular
>structure of the wood irreversibly compressed creating a permanent change 
  >in density and therefore buoyancy?
  >
  >   Thanks
  >
  >   Joe
  >
  >
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