Se7en
Contributor
Interesting post, UP
quote:
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Uncle Pug once bubbled...
In reality there is no NDL there is no finely drawn line on one side of which you have no need for decompression while on the other side you have a absolute need for decompression.
Every dive is a decompression dive
However the point at which this off-gassing becomes problematic is ill defined and many variables come into play beyond just the inert gas load itself.
To treat the so called NDL as a line which you can approach with impunity as long as you do not cross it is unwise. To use a computer to do so is doubly unwise.
It would be better IMO to gain an understanding of what the NDL represents and manage your dive accordingly. Plan on spending time shallow to offset time spent deeper . but not just because your computer told you to do a safety stop. Know what you are doing and why.
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Interesting post... you start off stating some diving facts quite succinctly - adding verisimilitude early in your post.
Then the implied message starts to seep through, the message that says you do know what you are doing, and the path you take is the right, or correct one. That other ideas are 'doubly unwise'
Yet you also, even though you claim not to, promote a level of safety that is as arbitrary as dive computer NDLs (Actually, it can be argued that as your methodology has recieved less emperical testing, it could be considered more arbitrary)
If we step backwards for a second, we can imagine that risk of DCS for any dive follows an exponential curve. As risk factors (not just time at depth, although that is a major one) increase, the chance of DCS increases. At first, only slightly, however, rapidly increasing as risk factors increase.
You stated the axiom "every dive is a deco dive" - which I do not think anyone can disagree with. However you seem to ignore the corollary to the axiom - that none of us fully decompress from any dive, we merely do whatever fraction of full decompression we deem adequate. (If we fully decompressed, all tissues would be at exactly ambient pressure when we surfaced)
Now, I would suggest that multiple dives can result in a diver being at the same point on the curve - ie 30 minutes at 60 feet involves the same amount of risk (of DCS) as 25 minutes at 120 feet with about 15 minutes of deco... and a quick review of the pressure group or repetitive group of your favourite tables will show this to be more or less true.
So, what we as divers have to do, is define for ourself what point on that risk curve are we individually prepared to travel to, and then define some methodology by which we intend to ensure we don't go past that point.
And guess what? Dive computers are designed to do exactly that. Each dive computer is designed to designate a point on the risk curve, and indicate to the user how close they are to that point. By either NDL time, or minimum deco time, the computer is providing a measure of how close to that computers defined point the dive is.
(Note - I'm deliberately ignoring where exactly on the risk curve each computer defines it's safe point)
And what we as divers have to do is consider where on the curve our particular computer has set it's point, and decide for ourselves if we want to set our own point at the same place, more conservative, or more risky. If we decide to set our personal point at exactly the same place as the computer is set, then 'riding the NDLs' cannot be called unwise. It is instead, a rationally determined decision, a measure of the risk we have decided to accept.
And this, Uncle Pug, is where I take issue with your stance. You have decided on a point on the risk curve for yourself, and you construct a methadology to keep yourself inside that risk point. Fair enough, it's what everyone should do.
However, what you cannot claim is that your solution is any more correct, or 'wise' than is anyone else's. All you can say is that you have chosen a point on the risk curve that is different (perhaps more conservative) than theirs. You use your methods to get you out of the water inside your risk point, and I use mine. If I decide that my risk point is further along the curve than the computer I use, then for me, riding the NDLs of my computer, or doing minimal deco as indicated by it, is a conservative dive for me.
I know what I am doing and why. I am using my computer to track a point on the risk curve for me, because I have decided on the availiable data for that computer (and algorithm) that I am comfortable with diving to that risk point.
Anyway, that's just my opinion
Se7en
PS: Uncle Pug, if you could buy a computer which indicated exactly the maximum profile that you dive to, would you buy it?
quote:
--------------------------------------------------------------------------------
Uncle Pug once bubbled...
In reality there is no NDL there is no finely drawn line on one side of which you have no need for decompression while on the other side you have a absolute need for decompression.
Every dive is a decompression dive
However the point at which this off-gassing becomes problematic is ill defined and many variables come into play beyond just the inert gas load itself.
To treat the so called NDL as a line which you can approach with impunity as long as you do not cross it is unwise. To use a computer to do so is doubly unwise.
It would be better IMO to gain an understanding of what the NDL represents and manage your dive accordingly. Plan on spending time shallow to offset time spent deeper . but not just because your computer told you to do a safety stop. Know what you are doing and why.
--------------------------------------------------------------------------------
Interesting post... you start off stating some diving facts quite succinctly - adding verisimilitude early in your post.
Then the implied message starts to seep through, the message that says you do know what you are doing, and the path you take is the right, or correct one. That other ideas are 'doubly unwise'
Yet you also, even though you claim not to, promote a level of safety that is as arbitrary as dive computer NDLs (Actually, it can be argued that as your methodology has recieved less emperical testing, it could be considered more arbitrary)
If we step backwards for a second, we can imagine that risk of DCS for any dive follows an exponential curve. As risk factors (not just time at depth, although that is a major one) increase, the chance of DCS increases. At first, only slightly, however, rapidly increasing as risk factors increase.
You stated the axiom "every dive is a deco dive" - which I do not think anyone can disagree with. However you seem to ignore the corollary to the axiom - that none of us fully decompress from any dive, we merely do whatever fraction of full decompression we deem adequate. (If we fully decompressed, all tissues would be at exactly ambient pressure when we surfaced)
Now, I would suggest that multiple dives can result in a diver being at the same point on the curve - ie 30 minutes at 60 feet involves the same amount of risk (of DCS) as 25 minutes at 120 feet with about 15 minutes of deco... and a quick review of the pressure group or repetitive group of your favourite tables will show this to be more or less true.
So, what we as divers have to do, is define for ourself what point on that risk curve are we individually prepared to travel to, and then define some methodology by which we intend to ensure we don't go past that point.
And guess what? Dive computers are designed to do exactly that. Each dive computer is designed to designate a point on the risk curve, and indicate to the user how close they are to that point. By either NDL time, or minimum deco time, the computer is providing a measure of how close to that computers defined point the dive is.
(Note - I'm deliberately ignoring where exactly on the risk curve each computer defines it's safe point)
And what we as divers have to do is consider where on the curve our particular computer has set it's point, and decide for ourselves if we want to set our own point at the same place, more conservative, or more risky. If we decide to set our personal point at exactly the same place as the computer is set, then 'riding the NDLs' cannot be called unwise. It is instead, a rationally determined decision, a measure of the risk we have decided to accept.
And this, Uncle Pug, is where I take issue with your stance. You have decided on a point on the risk curve for yourself, and you construct a methadology to keep yourself inside that risk point. Fair enough, it's what everyone should do.
However, what you cannot claim is that your solution is any more correct, or 'wise' than is anyone else's. All you can say is that you have chosen a point on the risk curve that is different (perhaps more conservative) than theirs. You use your methods to get you out of the water inside your risk point, and I use mine. If I decide that my risk point is further along the curve than the computer I use, then for me, riding the NDLs of my computer, or doing minimal deco as indicated by it, is a conservative dive for me.
I know what I am doing and why. I am using my computer to track a point on the risk curve for me, because I have decided on the availiable data for that computer (and algorithm) that I am comfortable with diving to that risk point.
Anyway, that's just my opinion
Se7en
PS: Uncle Pug, if you could buy a computer which indicated exactly the maximum profile that you dive to, would you buy it?
