Jay,
I just sent a post with some of this subject matter you are speaking of, before I read this post. You make a good point about needing lift bags that don't spill there air if they hit the surface to fast. I was not aware there was lift bag systems that use a relief valve set up. It would be good to take a look at those bags and see what they are using. Since they are already designed to work for lifting objects perhaps very quickly for some models. Do you know of any brand names of these type of closed lift bags?
The pontoons I'm configuring to install on my K-250 should be a good shape, and held well enough to keep air from spilling out of them. Since they would only be letting air out of one or two properly sized tubes that go down below them. These tubes might perhaps be one or two feet long that go down to a large externally mounted thru hull valve, that is much like the ones used to let the air out of the MBT's on the conning tower, but facing down instead. Does that sound workable?
I'll need to work up some 3D models to allow use to better clean up the design.
Your resident pop off dreamer ;)'
Regards,
Wheres
From: bottomgun@mindspring.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Weight of Water VS. Buoyant Force of Air
Date: Fri, 5 Sep 2008 20:46:41 -0400
Brent,
I also forgot to add that now you might be able to better
understand why most submersibles use hard ballast tanks with bottom openings
that are normally left open. Closed tankage increases the complexity of
the system and leads to greater opportunities for failure, especially under
emergency conditions. The other side of this story, when using lift bags
to salvage or rescue a sub, it is better to use closed bags (with relief
systems) so that the “bubble” is not lost when the rapidly ascending
sub breaks the surface.
R/Jay
Jay K. Jeffries
Andros Is., Bahamas
A skimmer afloat is but a submarine, so poorly built it will not
plunge…
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig
Sent: Friday, September 05, 2008 3:59 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Weight of Water VS. Buoyant Force of Air
Jay,
If according to
my none exact testing method I did several years ago, of a plastic gallon jug
full of air, pulled just below the surface of freshwater in a
freshwater pool with no chemicals in it, with weights. A gallon of
air, which contains exactly 231 cubic inches, exerts 11 lbs. 10 ounces
(not sure that was the amount, might of been 10 lbs. 11 ounces of buoyant force
in 65 degree F, fresh water, at my altitude.
Also take into account
that the weight used to keep the gallon of air down was weighed out of the
water. So what weight it has would be different in the water of course.
But since we are comparing the weight of freshwater or saltwater vs. the
buoyancy force of air in fresh or saltwater, it might be ok to weigh the
weights out of the water.
So since a cubic foot
has 1728 cubic inches in it, there is 7.48 gallons in a cubic foot. Meaning
that if my test data is close to correct, that a cubic foot of air would
require about 83.119 lbs. to make neutrally buoyant in freshwater, like I
explained above. In other words a cubic foot of air will exert about 83 lbs. of
buoyant force on the upper areas of the container, which is holding the air
down below freshwater.
From what I could find,
freshwater weighs about 62.4 pounds per cubic foot (1 kilogram per
liter.). So this would seem to mean to me that we need to calculate the
ambient subs cabin air and then multiply that by about 83 lbs. per cubic foot.
Then design the upper areas of the cabin to with stand that with a FOS
of ones choosing.
I would like it if some
one could tell me if my data on the amount of buoyant lift of air in freshwater
is reasonably correct. As well as what the number is for air in saltwater
or a general specific gravity of ocean waters.
Fresh
Water
Salt Water
62.3
lb/ft^3
64.0 lb/ft^3
____________________________________________________________________
I found this
data below in my World Book encyclopedia.
"Laws of hydrostatics describe the behavior of liquids at rest.
One principle of hydrostics state: The pressure
caused by the weight of a column of fluid is determined be the height of the
column. The shape of the column does not affect the pressure that is exerted by
the fluid.
Suppose that a pipe extends in a zigzag pattern from
the ceiling to the floor. Another pipe of equal diameter extends straight down
from the ceiling to the floor. The second pipe is, or course. shorter than the
first. If both pipes are filled with water, the longer one will hold more
water. But the water pressure at the bottom of both pipe will be equal, because
the height of both columns of water is equal.
An illustration of the above principle is the buoyant
force exerted by a fluid on an object submerged in it. The bottom of an object
submerged in water is deeper then the top of the object. Therefore, the column
of water pressing on the bottom of the object is taller then the column
pressing on the top of the object. Thus, the water exerts an upward force on
the object, called a buoyant force. Buoyant forces act to keep boats afloat.
Archimedes' principle comes from the principle
discussed above. It states: An object placed in a fluid seems to lose an amount
of weight equal to the weight of the fluid it displaces. A buoyant force
exerted on the object by the fluid causes the apparent loss of weight.
Archimedes, a Greek mathematician, developed this principle during the 200's
B.C.
To illustrate this principle, image that a 1-liter
metal can is placed in water. If the can weighs 3 kilograms, it will displace 1
liter of water, which weights 1 kilogram. Thus, the buoyant force equals 1
kilogram. The can will then seem to weigh only 2 kilograms-that is, 1 kilogram
less than it's original weight.
Pascal's law state: A fluid in a container transmits
pressure equally in all directions. Blaise Pascal, A French scientist and
mathematician, developed this law during the A.D. 1600's."
So if we use
Archimedes' principle and we place a gallon or air, that basically weights
nothing, in water it will not displace any water, unless forced down below to
surface like the air in are subs.
Your resident pipe dreamer ;)'
Regards,
Szybowski
From:
bottomgun@mindspring.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Upward Buoyant Pressures on Ambient Interior
Surfaces
Date: Thu, 4 Sep 2008 18:58:20 -0400
Brent,
Two things need to be sorted
out in this mental exercise. How many cubic feet of air? Convert
this into the weight of the equivalent volume of water…this is the force
pushing up. Now have many square inches of surface (upward side) is that
air applied to? Divide the force (equivalent pounds of water) by this
surface area and you have the PSI sensed by the interior overhead. As you
descend, the bubble gets smaller is no air is added, buoyancy decreases, and
the applied air pressure to the top surface decreases. Water force inside
and out are the same for an ambient sub.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
Talk sense to a fool and he calls
you foolish.
- Euripides
(484 BC - 406 BC)
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig
Sent: Thursday, September 04, 2008 6:34 PM
To: PSUBSorg
Subject: [PSUBS-MAILIST] Upward Buoyant Pressures on Ambient Interior
Surfaces
Upward Buoyant Pressures on Ambient
Interior Surfaces
Grand Greetings
SMMOM's ;)'
I've been pondering
this question for some time now, when I was designing a couple if different
ambient subs in my head. Doug, I believe brings up some good points
below about the higher PSI inside the ambient subs being a little higher. He
also made a point recently about the PSI being a little higher from the
constant flow of air, coming into the cabin for breathing.
I was thinking that
there is one more thing item we need to consider. That being that air is
really buoyant, as we all know. So one of the main reasons that 1 ATM
subs are so heavy, is that they need to counter act the buoyant forces that the
air in the interior is exerting upwards. So that means to me that all the
air in the ambient subs cabin is mostly pushing upward on any surface that's
there. This is why I was thinking that a hatch and/or any windows and
frame work can handle that amount of buoyant pressure that is trying to lift
the sub, and will do so, if you release a drop weight. For some large ambient
cabin spaces, I would think that pressure might be substantial. Any
thought? I wouldn't be surprised if I missed some thing.
Your resident bubble
dweller ;)'
Regards,
Szybowski
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] depth indicator
Date: Fri, 29 Aug 2008 09:55:57 -0400
From: djackson99@aol.com
I think the correct answer is
"almost" no difference.
Take a
4 ft pipe.
Cap one end and anchor the
open end to the bottom of a lake so that the cap is just below the surface.
Now fill the pipe completely with air. At the open end of the pipe the air
pressure is equal to the water pressure and a depth indicator will read the same
if it is inside or outside the pipe. But at the top of the pipe the water
pressure outside the pipe is zero and the air pressure inside the pipe still
indicates the pressure for 4ft of water.
So my dive computer outside the view port will indicate the depth of the view
port, and inside it would indicate an additional 3+ feet, to were I release air
into the surrounding water.
Best of Luck
Doug
www.submarineboat.com
-----Original
Message-----
From: Jay K. Jeffries <bottomgun@mindspring.com>
To: personal_submersibles@psubs.org
Sent: Fri, 29 Aug 2008 5:01 am
Subject: RE: [PSUBS-MAILIST] depth indicator
In ambient sub senses the
same pressure inside or out so there is no difference having the gage inside or
out.
Talk sense to a fool and he calls
you foolish.
- Euripides
(484 BC - 406 BC)
Hmmmm... Not the weight of the sub. It should indicate the
depth of the vent where the
air is released into the surrounding water and likely a little deeper since the
constant flow of air may add a few psi to the ambient cabin. Air at the
top of the cabin is at the same pressure as the air at the bottom of the cabin
where it is vented to the surrounding water. So it does not matter where
the gauge is inside the cabin.
That also makes the air at the top of the cabin at a pressure higher than the
water surrounding the top of the cabin. So a hatch in the top of an ambient sub
seals naturally if it opens inward. Completely opposite to a 1ATM sub.
In my case the dive computer is going to ride along outside the forward view
port. There is no room for it inside and with it outside it will automatically
start logging the dive when it submerges.
So what are you thinking of building?
Doug J
www.submarineboat.com
In an ambient submarine, if one
uses a dive watch type depth indicators to give an indication of how deep He
is, does this display the actual depth or will it be off a little having the
additional weight of the sub working on it? One of those HMMMM thoughts...
David Bartsch
Be the filmmaker you always wanted to beearn
how to burn a DVD with Windows. Make
your smash hit=
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