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: Thu, 10 Nov 2005 15:51:58 -0500
No change in weight, but weight is not displacement. You can spread out a
lead sheet and make a toy boat that floats from it or crumple it into a
ball that sinks
and its weight is the same, but its displacement was different when spread
out and EXPANDED. Same with air.
Bill.
----- Original Message -----
From: Paul Kreemer
To: personal_submersibles@psubs.org
Sent: Thursday, November 10, 2005 12:14 PM
Subject: Re: [PSUBS-MAILIST] Forces of Nature
That sounds right to me Dan, I bet you'd have a small buoyancy change as
the cabin bled air over time. That compressed air volume in the cabin
weighs a little bit but I'm not sure if it's important compared to you and
the sub. Here are some numbers:
Take a dry ambient compartment that's 60 cubic feet (about 3 ft diameter
by 8 ft long). The standard weight of air is 0.0766 lb/cf at sea level
which gives a cabin air weight of 4.6lbs on the surface and 18.4lbs at
100ft down. So you'd gain about 14lb of cabin air weight while descending
to 100ft.
But like you say, the air came from onboard flasks so there's no overall
change in the weight of the boat!
Paul
On 11/10/05, Daniel Edwards <dan_f_edwards@hotmail.com> wrote:
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
> >
> >
> >
>************************************************************************
>
>
>************************************************************************
>
>
>************************************************************************
> >The personal submersibles mailing list complies with the US
Federal
> >CAN-SPAM Act of 2003. Your email address appears in our database
>because
> >either you, or someone you know, requested you receive messages
from
>our
> >organization. If you want to be removed from this mailing list
simply
>click
> >on the link below or send a blank email message to:
> >removeme-personal_submersibles@psubs.org Removal of your email
address
>from
> >this mailing list occurs by an automated process and should be
complete
> >within five minutes of our server receiving your request.
PSUBS.ORG PO
>Box
> >311 Weare, NH 03281 603-529-1100
>
>
>************************************************************************
>
>
>************************************************************************
>
>
>************************************************************************
>
>
>
>
>
>
************************************************************************
>
************************************************************************
>
************************************************************************
> The personal submersibles mailing list complies with the US
Federal
> CAN-SPAM Act of 2003. Your email address appears in our database
> because either you, or someone you know, requested you receive
messages
> from our organization.
>
> If you want to be removed from this mailing list simply click on
the
> link below or send a blank email message to:
> removeme-personal_submersibles@psubs.org
>
> Removal of your email address from this mailing list occurs by an
> automated process and should be complete within five minutes of
> our server receiving your request.
>
> PSUBS.ORG
> PO Box 311
> Weare, NH 03281
> 603-529-1100
>
************************************************************************
>
************************************************************************
>
************************************************************************
************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003. Your email address appears in our database
because either you, or someone you know, requested you receive
messages
from our organization.
If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
removeme-personal_submersibles@psubs.org
Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.
PSUBS.ORG
PO Box 311
Weare, NH 03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************