Deep stop question

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I used to be of this mind, and a thoroughly unnecessary search of my long past posts will find ones in which I cautioned against ascending too slowly while using tables, arguing that the numbers on the tables were invalid if you were not ascending at the rate at which the tables were created
I have it first hand from the dude who was central in developing those tables that they weren't quite valid if you ascended too slowly.

EDIT: That said, neither I believe that ascending a little bit slower would lead to an unacceptable risk of getting bent, and I'm pretty certain that having us ascend at that particular rate was yet another exercise intended to challenge us a little bit.
 
I have it first hand from the dude who was central in developing those tables that they weren't quite valid if you ascended too slowly.
You talked with Rogers? Or was it Michael Powell? The person who told me was also involved.

Having read all the research on NDL ascents I could find last year, I urge you to get your contact to publish that information, since no one I encountered knows about it, including apparently DAN and PADI leaders.
 
In my research, I talked with someone who was well versed in the research done on the PADI tables, and he told me that wasn't true. He said they saw no problems associated with ascending slower than the 60 FPM used for the tables.
I have it first hand from the dude who was central in developing those tables that they weren't quite valid if you ascended too slowly.
Obviously, there is something here I do not understand.
Suppose I use the RDP to dive air to 30m; my NDL is 20 mins. After 10 mins I leave the bottom, so I'm in Group E.
But I ascend at 1m/min. I takes me 25 mins to get to my safety stop, then 3 mins at the safety stop, so 28 mins to surface.
The RDP assumes I was ascending at 18 m/min? Or, no faster than 18m/min? If, in fact my ascent was at 10m/min, then it takes me only 2.5 mins to get to my safety stop, plus 3 mins there, so 5.5 mins to surface. I could not "legally" surface faster than 25/18 mins to the SS, or 4.4 mins to surface. So all these are the same WRT dissolved gas in my body? Surface in 4.4, 5.5, or 28 mins?
Not likely. The slow surfacing means 25 mins below 5 m, so that's like maybe 25 mins at 18m of additional on-gassing?

I can only conclude that there is an ascent rate that is too slow and which invalidates the RDP, so must also assume BoulderJohn's contact was saying that slower than 60 fpm is OK..... but neglected to say so long as it is not too slow.
 
I can only conclude that there is an ascent rate that is too slow and which invalidates the RDP, so must also assume BoulderJohn's contact was saying that slower than 60 fpm is OK..... but neglected to say so long as it is not too slow.
Of course that was the assumption. You can always take it to an extreme. At some point you would violate NDLs. At some point you wouldn't even be ascending. Without stirring up troubles by being too specific, one of the earliest proponents of deep stops (in deco diving) advocated a deep stop approach such that the first stop on a 200 foot dive would be at 200 feet. That's pretty slow.


I remember one specific NDL dive I did that was pretty similar to countless other dives I and others have done. It was in Curacao. We were told that there were garden eels at about 100 feet. I dropped to that depth and watched them for a couple minutes before working my way up the reef. My total dive time was about 80 minutes, and I never violated NDL. I probably left the bottom at about 5 minutes from the start of my descent. According to the PADI tables, I had 5 minutes of bottom time before ascending at an average rate of less than one foot per minute.
 
My total dive time was about 80 minutes, and I never violated NDL.
Only because you were on a computer!
I thought we were talking about tables....
 
Only because you were on a computer!
I thought we were talking about tables....
Yes, we were, and I should have added that there is nothing in the PADI tables that would have said my ascent was invalid.
 
You talked with Rogers? Or was it Michael Powell?
No, it was Jan Risberg. And I've talked with Andreas Møllerløkken and Ingrid Eftedal on several occasions.

Norske dykke- og behandlingstabeller : English

Having read all the research on NDL ascents I could find last year, I urge you to get your contact to publish that information, since no one I encountered knows about it, including apparently DAN and PADI leaders.
I'm not a hyperbaric scientist. I try to learn from them, and I cite them when I think it's appropriate in informal situations, but trying to get something published in that field? That would take a lot more hubris than I've got.
 
does that direct surface assume a steady 30 fpm? IF so Ok what about those that do a higher ascent rate untill they get to 50 or 60 to reduce gass use would that deep stop for a minute maybe 2 be beneficial on over all gass usage? Im thinking no if you stop more than a minute.

That's one of the worms in the no-stop can: your surfacing supersaturation is computed from something that hasn't happened yet: the ascent. So there is some predefined ascent rate in there, most likely the recommended 30 fpm, but you won't really know unless the vendor spells it out for you or lets you read the code. If you deviate from it, theoretically you could invalidate the computed NDL.

It shouldn't ever happen in practice, but mathematically it's possible.

However once you actually stop, that may change things. E.g. if your fastest TC is 2.5 minutes, a one-minute stop may be long enough to on-gas it -- if it wasn't saturated at that depth (this is the part where they started calling it "profile-dependent"). If your fastest TC is 5 minutes, one minute is probably negligible even if it is on-gassing, but 2 minuets may not be.
 
No, it was Jan Risberg. And I've talked with Andreas Møllerløkken and Ingrid Eftedal on several occasions.

Norske dykke- og behandlingstabeller : English
When you said "those tables" to contradict my comment about what I learned about the research on the PADI tables, I assumed you were talking about the PADI tables.

So did they publish anything along those lines? Is there any official warning about it?
 
I remember one specific NDL dive I did that was pretty similar to countless other dives I and others have done. It was in Curacao. We were told that there were garden eels at about 100 feet. I dropped to that depth and watched them for a couple minutes before working my way up the reef. My total dive time was about 80 minutes, and I never violated NDL. I probably left the bottom at about 5 minutes from the start of my descent. According to the PADI tables, I had 5 minutes of bottom time before ascending at an average rate of less than one foot per minute.

But you did violate the NDL according to the planner, 100' max depth with a run time of 80 minutes is way over the 20 minutes max allowed - correct?

What is the correct way of defining the "time" under any given depth in the PADI RDP - I was of the understanding it was total bottom time but I've also heard it said as total time under the water....???

I get what you are saying about the no set too slow ascent rate but in that sense, defining time as the total time under water sort of covers that....

What am I missing? Welcome back, always appreciate yours and others insights.
 

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