brething underwater

[_memento]

since it's almost winter and there will be no more dives for me this year it's time to think about next summer and buy/build gear.
spearfishing went great this summer in the black sea, caught mostly small fish but tons of it, and i was trying to think of a way to extend my time under. most of the times i dived was under 25 ft, since most of the fish inhabit the shallow waters. personally, i hate going up for air, even if i only do it through the snorkel. for me it ruins the whole experience of freediving or underwater hunting, it takes away most of the freedom.

now i don't want anyone calling me stupid for what i am about to ask. i haven't done any research, and i am asking here because i thought that if it's impossibile, or harmful, it's better if someone tells me straight up than if i find it out through research or...practice (might cross my mind you know....). so here goes:

if i only had to go up to 5 ft or 10 ft to get air, it would be perfect. then i could probably stay under a lot longer (preferably at least 3-4 normal dives' time). so i was thinking of attaching a fine piece of tubing to a small diving buoy. on the sunken end it would have a one way valve so that no water goes in. also a weight close to the end so that it would hang down in the water, not float aimlessly.
now my questions would be....
1)are human lungs strong enough to bring air down to a certain depth (or do i need a small pump??) ? what depth would that be??
2)what depth would i have to be at so that the surface air would not be harmful to me?
3)how long would it be safe to be submersed like this for?

pic

[Pezman]

_memento,

I don't want to disparage your idea, but it has a number of pitfalls. First of all, you need about 6/33 * 15 psi = almost 3 psi to get the air down to 6 feet and 10/33 * 15 PSI = almost 5 psi to get the air down to 10 feet. With great effort, you may be able to draw air down to 3 feet, but you will not get a full breath and the effort will hurt your bottom time. You are better off surfacing.

If you use a pump, then you will need to be very careful to exhale whenever you go above the point at which you inhaled the air. Going as little as 3 feet above that point can result in a potentially fatal injury (embolism, ruptured lung etc.)

Basically, this contraption is a manual SCUBA system (well, "UBA" since it's not self contained). Some guys have made diving bells, which are similar to what you are proposing -- you basically pump air into a submerged chamber and use that to breathe. However, these contraptions are very dangerous for freedivers.

At any rate, if you do this and live to tell about it you can stay down for a pretty long time without incurring a decompression obligation as long as you're at or above a certain depth. If I remember the decompression tables, that depth is 20' but don't take my word for it.

I think that the idea has too many problems to bother pursuing, but if you do you should at least take a SCUBA course in order to learn about the physics and physiology of breathing compressed air.

[_memento]

well then i'll be the first to call this a BAD IDEEA. i had pretty muh guessed it was one.
but if we're already here, why not think of some way to implement in real life situations the freediver's need to NOT GO UP.
the first thing that comes to mind is that as you pump air with a pump through a tube, the pressure of the water surrouning it compresses it to a larger and larger degree as it goes downwards. so basically the problem is in finding a tube system that does not pass on the pressure to the air. again, this is off the top of my head and i will look into it and into any other options, but i urge everyone else to do so too.
until a way is found for a freediver to remain submerged for a much longer time than his own breath, and to do so without any adverse effects, then we are only men playing in the water, not truly belonging there.

[donmoore]

Memento,
You might want to look at the hookah diving system which is a surface pressured system. But like Pezman said, take a scuba course first so you understand the needed science to stay alive.

One thing that I have always wondered with hookah systems is why don’t they make a model with a return hose for the exhale. If your going to have a line come all the way down to you, then why not take the nosy part of breathing pressured air, the escape of air from the exhale, and send it quietly up a tube to the surface? Maybe it’s the hose compression thing you mentioned or maybe it’s just the fact nobody makes a dive regulator with a hose attachment to the exhaust.
don

[_memento]

i looked into the hookas diving system and it certainly takes the "free" out of "freediving"
i mean i'd rather surface than have a hose stuck to my face all of the time.

[Murat]

One of my friend (old spero) tried that. And told me that pressure of the water out side the tube compress the diameter of the tube and makes it closed somewhere else. So physically you have to had enough pressure in the tube to fight against that under water pressure. This is impossible with open end tube coz the air pressure is 1atm (760mm hg) but this is less than the water pressure at almost any level.

The only related system that i saw some old movies is one with connected with compressor at the open end. And this compressor can be carry in the boat. And needs energy to operate that. So it seems not suitable for freedivers...

[Beaky]

Originally posted by _memento
...until a way is found for a freediver to remain submerged for a much longer time than his own breath...

But then it wouldn't be freediving anymore would it? Sounds more like scuba to me anyway.

But then, if someone came up with a new scuba system which didn't weigh a ton, and you were able to move freely with, I might give scuba a second chance...

// Johnny

[_memento]

no, it would still be freediving. you wouldn;'t carry the air supply with you, but it would be submrged at a certain depth. it would be like coming up for air, only you wouldn't have to actually come up at all.

[SpearSlinger1]

How about the old diving bell? That would give a certain location to swim back to for air without having to surface. But before anything is undertaken I suggest exploring all the safety issues. Breathing anything at depth will increase the chances of DCS hit, embolism, etc. Another consideration is what if you had to bail out of the dive for whatever reason? Could the diver make it back to the surface without whatever kind of breathing system he had?