Need answer to something I've always Wondered About - Page 4 - SailNet Community
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post #31 of 50 Old 07-21-2013
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Need answer to something I've always Wondered About

Got as far as slowbutsteady's post on page one and made it no further I'll have to try again later.

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post #32 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

As kids snorkelling on the Great Barrier Reef, we sometimes used a large tough clear plastic bag that was held open at the mouth with a wire frame weighted at the corners and sunk a few feet to the bottom, to provide a few lungfuls more air before we needed to head back to the surface.

You might be able to do something like this with a hose and one-way valve fitted to the top of the bag, breathe in through it and exhale through the mouth...but we never got sophisticated enough to try it.. and I imagine you'd need a really large bag to get more than a half dozen breaths out of it.

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post #33 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

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Originally Posted by minnow1193 View Post
As far as water pressure and being able to breathe, isn't that why we have a rib cage? I would think the ribs would maintain room for some volume of air at minimal depths?
No, ribcages are there to protect your heart and lungs. The problem isn't "having room" to fit some air, it's the need to pressurize that air to the same pressure as the surrounding water. Without a compressor or a tank of compressed air, your lungs and diaphragm have to provide that pressure.

It's interesting that the number 3 feet was floated (heh) in this thread, because that's typically understood to be the smallest change in depth that could rupture your lungs if you hold your breath with full lungs. In other words, taking a full breath at 3 feet of depth, then rising to the surface, could rupture your lungs as the pressure is lowered and the air expands. And the first three feet are the deadliest--going from 3 feet to 0 is far more dangerous than going from 21 feet to 18.

I actually tried this when I was a kid (before some physics classes and scuba training made me understand what I was trying to do.) I took a garden hose into my pool and held onto the bottom rung of the ladder while trying to breath. Setting aside the issue of getting fresh air from a hose that long, my 16 year old lungs were not able to take a single breath at whatever the depth was...probably 3 to 4 feet.

I cringe when I read these threads about breathing from a surface supply, and I advise against it without scuba training. It's one of those "don't know what you don't know" things.
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post #34 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

So, honestly - if I hooked up my CPAP with blows a constant 8 cm of air to my nose, and breathed out with my mouth
Would that work to get me air while un-snagging a prop at 3 feet down?

CPAP for those that don't know:

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post #35 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

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Originally Posted by scratchee View Post
No, ribcages are there to protect your heart and lungs. The problem isn't "having room" to fit some air, it's the need to pressurize that air to the same pressure as the surrounding water. Without a compressor or a tank of compressed air, your lungs and diaphragm have to provide that pressure.

It's interesting that the number 3 feet was floated (heh) in this thread, because that's typically understood to be the smallest change in depth that could rupture your lungs if you hold your breath with full lungs. In other words, taking a full breath at 3 feet of depth, then rising to the surface, could rupture your lungs as the pressure is lowered and the air expands. And the first three feet are the deadliest--going from 3 feet to 0 is far more dangerous than going from 21 feet to 18.

I actually tried this when I was a kid (before some physics classes and scuba training made me understand what I was trying to do.) I took a garden hose into my pool and held onto the bottom rung of the ladder while trying to breath. Setting aside the issue of getting fresh air from a hose that long, my 16 year old lungs were not able to take a single breath at whatever the depth was...probably 3 to 4 feet.

I cringe when I read these threads about breathing from a surface supply, and I advise against it without scuba training. It's one of those "don't know what you don't know" things.
Funny, I did the same thing as a kid, except used a clear tube about 1/2 inch in diameter and 10 feet long. Didn't work for me either, even 1 foot under water could not "pull" a breath of air. Many years later I became SCUBA certified and understood why it didn't work. Now use my SCUBA tanks to clean the bottom and prop. Good explanation you provided.
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post #36 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

I don't feel like I know enough on the subject to make definitive statements for or against the theory that the EXTERNAL pressure at 6ft would create difficulty in inhaling non-compressed air, but it certainly sounds plausable.

The re-breathing of CO2 and resistance of the hose issues are easily enough to get around, as has been discussed before.

The garden hose in the pool while 16 years old is a decent experiment. To prove the theory I'd want to see a lot less resistance though. Some hoses are 1/2" inside diameter, and unless it was a cut length, you were trying to pull it a long way...

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post #37 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

I played with this idea in my pool today, in 6 ft of water it was virtually impossible to breath with 6 1/2 feet of 1" tube. I just couldn't exhale enough to clear the tube and after about a minute had to surface.
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post #38 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

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Originally Posted by azguy View Post
I played with this idea in my pool today, in 6 ft of water it was virtually impossible to breath with 6 1/2 feet of 1" tube. I just couldn't exhale enough to clear the tube and after about a minute had to surface.


Dang, that was looking promising for a while.

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post #39 of 50 Old 07-22-2013
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Re: Need answer to something I've always Wondered About

Breath in through your mouth and out your nose resolves the co2 issue. Being able to suck air in another point.
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post #40 of 50 Old 07-23-2013
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Re: Need answer to something I've always Wondered About

I also tried this as a teenager. I couldn't inhale at much more than a foot. Tube diameter has nothing to do with it. It's just pressure differential.

"As kids snorkelling on the Great Barrier Reef, we sometimes used a large tough clear plastic bag that was held open at the mouth with a wire frame weighted at the corners and sunk a few feet to the bottom, to provide a few lungfuls more air before we needed to head back to the surface."

This works because the air in the bag is pressurized to the same pressure as the water. The danger is that if you breath from the bag and then rise to the surface with out exhaling, your lungs will burst.
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