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Alcyone
Guest
I've possible trained 50+ divers over 20 years, few have struggled so manfully with the basic concepts!
Diving
- Thread starter deeb
- Start date
I've possible trained 50+ divers over 20 years, few have struggled so manfully with the basic concepts!
tcm
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Hum. The basic concepts have actually been explained to *you*, not the other way around. You gave silly analogies of fishtanks then car tyres, all shot down in flames. You even said you would appreciate it when people accepted they were wrong, but then you didn't.
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Alcyone
Guest
My figures are there. You have not shot them down in flames. You have ignored them. If you would like me to explain them to you one step at a time, we can do that. If you would like to explain where the flaw is, you can do that.
If you want to shout 'rubbish' with no attempt at refutation of any of the figures, that's fine too.
Take your pick.
tcm
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well, unfortunately, yes i (and several others) have shot your silly arguments to pieces and nobody has supported those analogies.
Despite your insistence, breathing/being a metre underwater isn't like having 750kg on your chest (yet you think it is) and nor is the air pressure in a vehicle tyre dependent upon the vehicle's weight.
I spose that to some people, training 50 people in twenty years only *barely* qualifies you as an instructor, but at least you aren't a physics or maths teacher. Heyho.
Despite your insistence, breathing/being a metre underwater isn't like having 750kg on your chest (yet you think it is) and nor is the air pressure in a vehicle tyre dependent upon the vehicle's weight.
I spose that to some people, training 50 people in twenty years only *barely* qualifies you as an instructor, but at least you aren't a physics or maths teacher. Heyho.
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Alcyone
Guest
Stop the name calling and address the issue. Do you want me to go through the maths with you, yes or no?
tcm
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Um, well, how about you show us some Welsh instead? I mean - we've already seen your maths, physics, use of latin etc thanks, and it wasn't really much kop, was it?
You're gonna have to do some really incredible (and wrong) mathematics to prove that being a metre underwater is just the same as having 750kg on your chest - and I even offered a practical verification of your results. Are you gonna admit that was rubbish (and the tyre things as well) or do that stomping off again? I don't want to leave info on the forum unchallenged to the effect that "being a metre underwater is like 750kilos on your chest" cos it's not correct, that's all. And it was *you* who said that you appreciated people admitting when they're wrong?
You're gonna have to do some really incredible (and wrong) mathematics to prove that being a metre underwater is just the same as having 750kg on your chest - and I even offered a practical verification of your results. Are you gonna admit that was rubbish (and the tyre things as well) or do that stomping off again? I don't want to leave info on the forum unchallenged to the effect that "being a metre underwater is like 750kilos on your chest" cos it's not correct, that's all. And it was *you* who said that you appreciated people admitting when they're wrong?
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Alcyone
Guest
That's a no then. Cheers.
How about this then, from NASA (you might call them Nasums)?
http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/fluid_pressure.html
There are two examples in there of divers and the tonnes of pressure they are under, tens of tonnes in fact. It's in kPa, but I can help you do the conversion if you struggle with Google.
lw395
Well-Known Member
I think it might be worth putting the analogies aside and remembering the principles:
Water has a density of 1000 kg/m3
pressure=force/area
pressure=1000kg/m2 per metre depth approx
Relatively small changes in depth can therefore generate enough force to do damage.
The change in pressure from 10m down to the surface is the same as from atmospheric to total vacuum. Perhaps that is a clearer indicator of the potential for damage?
I'm going swimming now, and will remember to clear my ears as I go to the bottom of the pool.
Cheers
Water has a density of 1000 kg/m3
pressure=force/area
pressure=1000kg/m2 per metre depth approx
Relatively small changes in depth can therefore generate enough force to do damage.
The change in pressure from 10m down to the surface is the same as from atmospheric to total vacuum. Perhaps that is a clearer indicator of the potential for damage?
I'm going swimming now, and will remember to clear my ears as I go to the bottom of the pool.
Cheers
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Alcyone
Guest
Exactly.
tcm
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Ok - feel free - do some maths that proves that being 1metre underwater is like having 750kilos of fish tanks (or other items to a same weight) on your chest. Then to validate your results (cos i and nobody else will believe it) start loading weights on to your chest. I think ( i know) you'll feel very uncomfortable very soon.
You don't *really* think that being 10metres underwater is like have 7500 kilos loaded on to your chest, do you?
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Alcyone
Guest
It matters little what I think. Those are the facts, dear boy. At least, they would be if you didn't keep changing them............
tcm
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who's changing things? Not me.
We're waiting for you to prove that being approx 1foot underwater is like having a load of 250kg aplied to your chest and by extrapolation that being a metre underwater is 750kilos applied, and hence 7500kilos at 10 metres.
You can say you were wrong about this at any time yerknow?
We're waiting for you to prove that being approx 1foot underwater is like having a load of 250kg aplied to your chest and by extrapolation that being a metre underwater is 750kilos applied, and hence 7500kilos at 10 metres.
You can say you were wrong about this at any time yerknow?
tcm
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It matters little what I think. Those are the facts, dear boy. At least, they would be if you didn't keep changing them............
Who's changing things? Not me. We're waiting for you to mathematically prove that being a foot underwater is like having a 250kilo weight on your chest. By extrapolation, that means a 750kilo weight at a metre underater, and 7500 kilos at 10metres down.
You could just say you were wrong about this yerknow?
erm dual post, sorry..
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Alcyone
Guest
I've given you the figures. You refuse to discuss them. If you are going to try and wind me up, at least have the common decency to stick to the point.
tcm
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Now now, you're accusing me of name-calling, not having common decency and lots of other stuff.
Fact is one minute you say you'll prove it - next minute you say you won't.
Unless you prove otherwise, i think we can all take it as fact that going down under the boat 2metres isn't the same as having 1500kilos (6x 250kg, about a tonne and a half!) loaded on to your chest whilst lying flat on your back. Which you said it was, more than once.
It's you who launched into this thread claiming all sorts of huge dangers lurking. Yep, things are dangerous - but you're overstating those dangers, which is misleading.
Fact is one minute you say you'll prove it - next minute you say you won't.
Unless you prove otherwise, i think we can all take it as fact that going down under the boat 2metres isn't the same as having 1500kilos (6x 250kg, about a tonne and a half!) loaded on to your chest whilst lying flat on your back. Which you said it was, more than once.
It's you who launched into this thread claiming all sorts of huge dangers lurking. Yep, things are dangerous - but you're overstating those dangers, which is misleading.
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Alcyone
Guest
No, my dear boy, it is you that are misleading folk. Why do you feel that you cannot breath through a snorkel 2 feet long (you can Google that if you don't believe it)? Because the weight of water prevents the diaphragm from opening the lungs. It is as though a large portly gentleman was sitting on your chest, or a fishtank if you like.
So tell, me, TCM, what is the pressure of water 1ft below the surface, you can do it in pounds per square inch, or kg per cm. Let's see if you want to be serious.
Can you answer? Explicitly?
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Elemental
Well-Known Member
This is really interesting (except for the parts where you trade insults with each other...
) It's one of those discussions where the numbers (as put forward by Alcyone) don't seem to add up to the observed facts even though they're correct ISTM.
I am not a diver.
I have snorkelled and when I've snorkelled down to 3m or so I haven't been aware of crushing forces surrounding my body. However I am clearly swimming around with an enormous mass of water directly above me. I have also tried to breathe through a long hosepipe whilst underwater and struggled with the effort required to draw air into the lungs through it at even modest depths. I'm also aware that scuba cyclinders empty much quicker at depth due to a lungful (volume) of air at 10m depth being more massive (kg) than a lungful at the surface.
The fact that the pressure at depth operates from above, below and sideways on the bosy must have something to do with it, plus the fact that air is compressible (but the body isn't - being mainly fluid). If I took a balloon, filled it with water (no air) and then submerged it to 10m (or 20m or 30m) it wouldn't change volume/size would it? Yet the balloon clearly isn't very strong to support massive loads.
) It's one of those discussions where the numbers (as put forward by Alcyone) don't seem to add up to the observed facts even though they're correct ISTM. I am not a diver.
I have snorkelled and when I've snorkelled down to 3m or so I haven't been aware of crushing forces surrounding my body. However I am clearly swimming around with an enormous mass of water directly above me. I have also tried to breathe through a long hosepipe whilst underwater and struggled with the effort required to draw air into the lungs through it at even modest depths. I'm also aware that scuba cyclinders empty much quicker at depth due to a lungful (volume) of air at 10m depth being more massive (kg) than a lungful at the surface.
The fact that the pressure at depth operates from above, below and sideways on the bosy must have something to do with it, plus the fact that air is compressible (but the body isn't - being mainly fluid). If I took a balloon, filled it with water (no air) and then submerged it to 10m (or 20m or 30m) it wouldn't change volume/size would it? Yet the balloon clearly isn't very strong to support massive loads.
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Alcyone
Guest
This is really interesting (except for the parts where you trade insults with each other...
I am not a diver.
I have snorkelled and when I've snorkelled down to 3m or so I haven't been aware of crushing forces surrounding my body. However I am clearly swimming around with an enormous mass of water directly above me. I have also tried to breathe through a long hosepipe whilst underwater and struggled with the effort required to draw air into the lungs through it at even modest depths. I'm also aware that scuba cyclinders empty much quicker at depth due to a lungful (volume) of air at 10m depth being more massive (kg) than a lungful at the surface.
The fact that the pressure at depth operates from above, below and sideways on the bosy must have something to do with it, plus the fact that air is compressible (but the body isn't - being mainly fluid). If I took a balloon, filled it with water (no air) and then submerged it to 10m (or 20m or 30m) it wouldn't change volume/size would it? Yet the balloon clearly isn't very strong to support massive loads.
The figures are very counterintuitive. I have some fairly hefty qualifications and I didn't believe them when I was told, but they are correct, as you say.
Be very careful with long snorkel experiments. The possible results were highlighted by another poster above.
You are spot on with the cushioning effect, too, although I seem to remember reading that sea water is very slightly compressible. Something to do with the salt.
Incidently, I once took a crunchy bar to 30m for a bet. Nobody won. It melted. Seems the chemicals in a crunchy bar wdon't like 4 bar of pressure.
Not a lot of people know that.
tcm
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Ooh, you're trying very hard to wriggle out!
I contested specific pieces of YOUR misinformation - you say that being one foot underwater is the same as having 250kilos on your chest, Will you prove or otherwise withdraw this?
Yeah, I can answer your simplistic question, there's 15psi at sea level = equivalent of about 10m =33feet of water and so a foot underwater there's another 1/33 of that = tenth of a third of an atmosphere which is .5 psi, making 15.5 psi absolute ish.
Now, please return to the anology that being a foot underwater "is like having 250kilos on your chest whilst lying flat on your back" and confirm that that's not true. Or do you really think it is?
yankeebloke
Well-Known Member
Jeezzz
i just read through all 12 pages of this stuff!
I am also a scuba diver, but i am also a realist.
2m down....you can do it on a breath hold, but do try to remember to breath out as you come up, thats all needs said on that subject.
Scuba gear is a funny thing, some take to it straight away, others struggle to feel comfortable breathing underwater (its not natural)
I would recommend training if you are going to use scuba gear and be underwater its not as easy as it sounds.
But...............seeing how some will not accept that it is a danger, no matter who says what.
I believe it this point i have to allow the Darwins awards to come into effect.
either take the advise or do it your own way, when you are down and something goes wrong, and pannic sets in, well at that point your will either qualify for a lucky sod award and make it out, or a darwin award and make the next dive magazine article that shows how stupid untrained ppl manage to kill themselves while using scuba gear.
i just read through all 12 pages of this stuff!
I am also a scuba diver, but i am also a realist.
2m down....you can do it on a breath hold, but do try to remember to breath out as you come up, thats all needs said on that subject.
Scuba gear is a funny thing, some take to it straight away, others struggle to feel comfortable breathing underwater (its not natural)
I would recommend training if you are going to use scuba gear and be underwater its not as easy as it sounds.
But...............seeing how some will not accept that it is a danger, no matter who says what.
I believe it this point i have to allow the Darwins awards to come into effect.
either take the advise or do it your own way, when you are down and something goes wrong, and pannic sets in, well at that point your will either qualify for a lucky sod award and make it out, or a darwin award and make the next dive magazine article that shows how stupid untrained ppl manage to kill themselves while using scuba gear.
