Keeping up with Changing Thinking in Scuba

[dmaziuk]

Forum A: A reasoned discussion on why and to what extent deep stops are an appropriate component of decompression
Forum B: A reasoned discussion on why and to what extent deep stops should be minimized or avoided during decompression

There's these guys, knowhere.com -- they apply machine intelligence to news stories to sort out the spins from the facts and give you the latter with options "see the right/see the left". Sounds like just the ticket.

I welcome our AI overlords, the computer is my friend and I trust the computer.

 

[rsingler]

And that is why a dual forum debate will be most useful to the new Tec diver just starting to get his feet wet (so to speak).

TWO sides, dispassionately presented, with no diversion to useless spats.

Because in the end, we hear what we want to hear, and you have just proved it to me.

Dr. Mitchell apparently said,

"if you did the same decompression time, but distributed your stop time shallower, then you would almost certainly have less risk, The actual difference in risk might be relatively small, and perhaps not worth arguing about." (Dr. Simon Mitchell to me during one of our personal chats.)

What you may have heard:
The actual difference in risk [is]...not worth arguing about.

What I heard:
if you...distributed your stop time shallower, then you would...CERTAINLY have less risk

Dr. Mitchell is too much of a gentleman to be strident, and we each hear what we want to hear.

Reasonable men may disagree.
Some things will never change.
And other sayings...

Yeah, I think a dual forum would be nice.
But for me the crux of it is not even new news any more:

...In which there is 40 minutes of discussion, diagram and analysis, and Dr. Mitchell finishes by saying,
"I am diving...50/70 or 75..."
Well, that'll do it for me, for now.
Cheers! And safe diving to all of you.

 

[Blasto]

After realizing the insignificance of this deep stop debate, let us now try to market a Shearwater computer to the UTD folks. The marketing slogan would be something like this ...
"SHEARWATER PERDIX! THE 940.00 USD DIVE COMPUTER THAT MAKES YOU .0007 PERCENT SAFER!

No.
Yes, RD with reduced deep stops should, if calculated correctly, and if everything on the dive goes right, get its users out of the water safely enough.

But a Perdix, or for that matter any real dive computer, does much more than just shave 0.0007 or whatever off your risk of a chamber ride.

It's a computer that lets you execute dives well outside of the range of RD's applicability.
It's a computer that gives you safe and optimal deco guidance even when something goes wrong.
It's a computer that gets you out of the water in less time - with less hypotermia and less dehydration.
Computer profiles are safer because of the reduction in tissue stress - which also results in less fatigue after every dive.
Computer profiles keep you shallower - saving you gas and keeping you closer to assistance.
So it's a $940 investment that will soon pay off its price in helium.

But what can't be stressed enough is how much quicker a computer can get you out of deco. That's less time for things to go wrong, more gas left when they do, less gas required to handle it thanks to shallow depth, and less consequences if things do go wrong again.

 

[CAPTAIN SINBAD]

And that is why a dual forum debate will be most useful to the new Tec diver just starting to get his feet wet (so to speak).

TWO sides, dispassionately presented, with no diversion to useless spats.

Because in the end, we hear what we want to hear, and you have just proved it to me.

Dr. Mitchell apparently said,


What you may have heard:
The actual difference in risk [is]...not worth arguing about.

What I heard:
if you...distributed your stop time shallower, then you would...CERTAINLY have less risk

Dr. Mitchell is too much of a gentleman to be strident, and we each hear what we want to hear.

Reasonable men may disagree.
Some things will never change.
And other sayings...

Yeah, I think a dual forum would be nice.
But for me the crux of it is not even new news any more:

...In which there is 40 minutes of discussion, diagram and analysis, and Dr. Mitchell finishes by saying,
"I am diving...50/70 or 75..."
Well, that'll do it for me, for now.
Cheers! And safe diving to all of you.

I have read all that your posted.

When I am quoting Dr. Mitchell, I am cutting and pasting his words from our chats via PM. Those are his words exactly the way they were written to me.

 

[rsingler]

I have read all that your posted.

When I am quoting Dr. Mitchell, I am cutting and pasting his words from our chats via PM. Those are his words exactly the way they were written to me.

I believe you, Sinbad. I really do. I believe that is what Dr. Mitchell said. And yet we reach disparate conclusions...

It's all good! I won't disagree with you. But I might not quite dive your profile. And that's okay, too.

We pays our money, and we takes our chances...

 

[Jack Hammer]

I think the time and depth are very relevant. I have a buddy who still uses VPM, when we dive together our runtimes are very similar. 25-30 minutes bottom time, 150'-180'. Our tables are fairly similar and our computers are typically only a few minutes difference overall. We stick together for all stops as neither of us have minded waiting an extra minute at a stop for the other. And whoever clears first at the last stop does more deco waiting for the other to clear. On "shallower" and "shorter" dives like these the differences are minimal and probably not worth arguing about. It would be different on much deeper or longer dives and those differences could really add up. Perspective is important.

 

[KevinNM]

On "shallower" and "shorter" dives like these the differences are minimal and probably not worth arguing about. It would be different on much deeper or longer dives and those differences could really add up. Perspective is important.

On major expedition scale dives I'm not sure any deco approach really works. I'm taking like 6 hours to 400 feet stuff. I've gotten the distinct impression that this is a grey area at best. But since the odds that I'll ever feel confident dive to 400 feet is small (much less for 5 hours) it's not something I've ever really looked at.

 

[CAPTAIN SINBAD]

No.
Yes, RD with reduced deep stops should, if calculated correctly, and if everything on the dive goes right, get its users out of the water safely enough.

But a Perdix, or for that matter any real dive computer, does much more than just shave 0.0007 or whatever off your risk of a chamber ride.

It's a computer that lets you execute dives well outside of the range of RD's applicability.
It's a computer that gives you safe and optimal deco guidance even when something goes wrong.
It's a computer that gets you out of the water in less time - with less hypotermia and less dehydration.
Computer profiles are safer because of the reduction in tissue stress - which also results in less fatigue after every dive.
Computer profiles keep you shallower - saving you gas and keeping you closer to assistance.
So it's a $940 investment that will soon pay off its price in helium.

But what can't be stressed enough is how much quicker a computer can get you out of deco. That's less time for things to go wrong, more gas left when they do, less gas required to handle it thanks to shallow depth, and less consequences if things do go wrong again.

At recreational level, I did a few dives with UTD divers who were using bottom timers while I was using my computer. My computer did not give me any additional bottom time compared to Min-Deco that they were coming up with on their bottom timers. None!

At technical level, it is the best mix that lets you out sooner which is where computers become useful. A computer that is running a standard mix will really not do much would it? So I think it would make more sense if we do a best mix vs standard gases comparison instead of computers vs RD.

From the profiles I have run while comparing best mixes to standard gases, the decompression time you are eliminating on most profiles with your best mix is really not as much as I would have thought. If there is one ladder hanging from the boat then only one of us can climb at a time while the other will have to wait in the water at the hang bar regardless of whether our computer has cleared us or not. The time it will take for any one of us to swim up to the swinging ladder and climb up the boat, clear it for the second person will be 5 minutes? What good would a computer be for me that has shaven off 5 minutes of deco time if I happen to be the second one to go and you be the first when both our computers have cleared us at the same time? All these 5 minute "advantages" that the precision device is generating get eaten away by realities of life so I am good either way.

 

[CAPTAIN SINBAD]

On major expedition scale dives I'm not sure any deco approach really works. I'm taking like 6 hours to 400 feet stuff. I've gotten the distinct impression that this is a grey area at best. But since the odds that I'll ever feel confident dive to 400 feet is small (much less for 5 hours) it's not something I've ever really looked at.

I attended a seminar by Nuno Gomes who was telling us about his nearly 1000 ft cave dives. He was asked what algorithm he used at those depths and he said that all these algorithms are reliable down to 500 feet. After that, they become unreliable and you will be surfacing with symptoms no matter what algo you use. You have to note down your symptoms and then modify your next dive based on your symptoms from previous ones and have an understanding of decotime vs bottom time ahem... RATIOS.

As per my understanding the notion that RATIOS are more reliable than computers and established algorithms also comes from this context where the limits of all algorithms have already been exceeded. Agencies who propagated the idea of abandoning computers, monitoring symptoms and using ratios were doing extreme exposures where decompression algorithms have already collapsed.

On scubaboard folks seem to think that these agencies do not trust computers because electronics are not reliable! Some are saying that carrying a back up computer will eliminate the need for ratio deco and You can see pages after pages of debate about how a modern computer is actually more reliable that an SPG. No one looks at the extreme dives that Jarod Jablonski, Sheck Exley and Nuno Gomes were doing. No computer would get them out from the mess they were putting. It would be gauges, ratios and symptoms from previous dives that would guide the way.

 

[KeithG]

There are divers still believing reversed profile is BAD and to be avoided.
Some DC will also punish you with shorter ndl if you execute a reversed profile dive.

I am curious. Which computers?