Padi Advanced OW - Deep stops??

[Diverman68]

Shearwater petrel 2 all I use.

 

[Diver0001]

I guess the point of this for a no-stop dive will be that it doesn't matter what kind of stops you make during the ascent and whose name or study is cited in the manual (whether conclusive of inconclusive)..... It's all marketing. the difference is going to be marginal and statistically insignificant.

If there were a really compelling study that showed that the NDL's we have right now are fundamentally wrong, then we would have new algorithms, not new "bells and whistles". In the technical context there IS a legitimate discussion right now (has been for several years) because there is irrefutable proof that RGBM is broken ... IN THAT CONTEXT.

For recreational divers, studies like Morroni seem to suggest that we have a choice, but the fact of the matter is that it's all "drawing bright lines through a grey area". It is FAR more useful for marketing than it is for divers.

R..

 

[scubadada]

During the raging deep stops debate in the technical diving forum, I started a thread so that we could agree on a definition for the phrase "deep stop." That effort was a failure.

During the discussion among the experts in the 2008 DAN Deep Stop workshop that was intended to come to a consensus statement for the results of that workshop, the problem of the definition of the phrase was raised. They could not come to a consensus of a definition then, either. Some suggested just eliminating the phrase altogether. I think I am moving in that direction myself.

We all know that when we ascend, we must use some sort of strategy so that we can reach the surface without DCS. We all would agree that ascending a few feet and then stopping for 10 minutes is stopping too deep for too long. We would all agree that going directly to the surface from all but the shallowest dives would be stopping too shallow for too little time. Somewhere in between those extremes is the best strategy for that diver on that dive. The problem is we really don't know what that strategy is. Some people think that the first stop should be deeper than other people believe it should be. For me, that is all that is needed in a discussion, and trying to pin down a definition is not only unnecessary, it is counterproductive. In the raging debate in the technical diving discussion, that simple difference was missed by people who insisted that everyone follow their definition of deep stops rather than just talk about the search for an optimal decompression strategy.

Generically, these could be called no deco or recreational deep stops and deco or technical deep stops. For no deco deep stops, the stops are deeper than are prescribed by the decompression algorithm (no stop or SS). For deco deep stops it is not so clear. VPM generates a profile including what are called deep stops. One can accomplish the same thing by choosing a low GF lo when utilizing Buhlmann with GF. For me, recreational deep stops are some amount of time at around half the maximal depth. I'm not at all sure what technical deep stops are

 

[boulderjohn]

Generically, these could be called no deco or recreational deep stops and deco or technical deep stops. For no deco deep stops, the stops are deeper than are prescribed by the decompression algorithm (no stop or SS). For deco deep stops it is not so clear. VPM generates a profile including what are called deep stops. One can accomplish the same thing by choosing a low GF lo when utilizing Buhlmann with GF. For me, recreational deep stops are some amount of time at around half the maximal depth. I'm not at all sure what technical deep stops are

The same defintions apply to technical deep stops. The difference is between those added to an existing plan and those already incorporated into an existing plan (like VPM or Ratio Deco). Believe me, since I have to teach all of this to my students, and since I have to do the dives that will use on theory or another, I have encountered the definitions and worked hard both to understand them and teach them. Right now, things are very much in a state of flux. In technical diving, PADI's standards require that deep stops be taught and used in the trimix class. That curriculum also requires me to teach students to stay on top of the latest research. I wrote to PADI and told them that my reading of the latest research, which I share with my students, tells me not to do deep stops as defined by and required by the curriculum. Their response was that I was doing exactly the right thing by discussing the latest research with the students. If we decide that this research is going against deep stops, I am justified in skipping that standard. So far all students have agreed that we should not be doing those stops.

 

[dmaziuk]

I guess the point of this for a no-stop dive will be that it doesn't matter what kind of stops you make during the ascent and whose name or study is cited in the manual (whether conclusive of inconclusive)..... It's all marketing. the difference is going to be marginal and statistically insignificant.

If there were a really compelling study that showed that the NDL's we have right now are fundamentally wrong, then we would have new algorithms, not new "bells and whistles". In the technical context there IS a legitimate discussion right now (has been for several years) because there is irrefutable proof that RGBM is broken ... IN THAT CONTEXT.

For recreational divers, studies like Morroni seem to suggest that we have a choice, but the fact of the matter is that it's all "drawing bright lines through a grey area". It is FAR more useful for marketing than it is for divers.

R..

Oh good. So it appears we do have a consensus answer to OP's question "is deep stop option a significant feature of a recreational dive computer": no.

 

[Centrals]

As a side note does anyone do the 1 min stop at 3m or is it just me?
3 min at 6m, 1 min at 3m as the most bubbling off occurs there.
Extra safe or not worth it?

I will do that if the dive is deep(>30m) otherwise I just do a very slow ascent after a 5mins safety stop at 6m.

 

[KenGordon]

My Oceanic computers offer an optional deep stop for no deco dives only. It is a 2 minute stop at half the maximum depth of greater than or equal to 80 feet. The owner's manual cites the Morroni & Bennett study. I have never utilized this option. I do spend an extra couple of minutes at my SS if I have come within several minutes of deco. When doing light deco, I pad the shallow stop by 3-5 minutes, kind of like adding a SS after clearing the deco obligation. I dive the DSAT decompression algorithm. So far, so good, for me

If you are padding the stops you are not diving DSAT. You are diving something you have made up which is probably more concervative than DSAT and so says nothing about how effective DSAT is.

OP, these 'deep strops' are essentially a type of safety stop. Mostly they force a diver to control their ascent rate by actually stopping. By and large they can be ignored and perhaps the computer will add a minute at the final stop. If you have done a 42m dive and you get a minute at 22m and two at 11m it is unlikely you will on gas significantly at those stops. If you do those stops, then you will not have done a 20m/minute ascent to the surface. Avoiding such a fast ascent is worth while in my opinion.

Deco is a game of dice. People do get bent doing 15m, 45 minute dives. The idea is to reduce the incidence to an acceptable level.

The NEDU study mentioned above, is about trading deep time for shallow time. That was a particular claim made that by doing stops deeper then you could do less time overall for the same time on the bottom. That is not the case with these deep safety stops which are about extra stops, just deeper than 6m.

 

[DevonDiver]

Generically, these could be called no deco or recreational deep stops and deco or technical deep stops. For no deco deep stops, the stops are deeper than are prescribed by the decompression algorithm (no stop or SS). For deco deep stops it is not so clear. VPM generates a profile including what are called deep stops. One can accomplish the same thing by choosing a low GF lo when utilizing Buhlmann with GF. For me, recreational deep stops are some amount of time at around half the maximal depth. I'm not at all sure what technical deep stops are

The 'old' (Pyle) stops were unilaterally added to very plain Buhlmann profiles. They were added unilaterally by the diver post-planning, so the software-derived profile didn't subsequently track slower tissue on-gassing at the deeper stop/s. It caused bends.

Then came 'pure' bubble models...applying factors to limit bubble growth, but not tracking saturation. The belief was that this shortened deco.

In a nutshell, if microemboli were limited then there's no bubble to grow....so no need for long shallow stops. For a while it was seen as near-miraculous.... very short deco... but it was proven a false assumption as people started going into chambers.

Some recreational dive computers also added those Pyle-type stops in lieu of safety stops. I don't understand the reason for that, other than it being a gimmick the rode the 'deep stop bandwagon' at that time.

That recreational divers used these deep stops, without understanding them, and at the expense of shallow safety stops seem quite ludicrous now. (some still do..)

Most modern dual-phase algorithms used in computers include deeper stops to limit microemboli growth in the fast tissues, BUT they simultaneously track slower tissue on-gassing and resolve that with consequently longer shallow stops.

Dealing with microemboli has benefits, but it has to be paid for in the shallows.

 

[boulderjohn]

As I said above, we are in a state of flux, and a diver needs to be very careful in planning. Don't just implement some idea and combine it with another plan without truly understanding what you are doing and why.

I recently dived with a threesome that included a diver who was originally trained for deco diving by GUE, using no computer at all. He had supposedly decided to leave that approach and had purchased a Shearwater. The other diver and I were using Shearwaters following Buhlmann ZHL-16 with gradient factors of 40/80, and he said he would use that as well. We planned a multi-level dive with a maximum depth of 200 feet, using Multi-deco. It had our first deco stop at 70 feet. We all wrote that plan and 2 contingencies down, but we agreed that was our backup. We would otherwise follow the computers.

When we began our ascent, our computers had our first stop at 60 feet, and we gave the ascent sign and started up. We had not gone very far when the former GUE diver stopped. We hesitated for a while and then ascended to 60 feet. The visibility was good, so we could see him clearly, and I kept my light pointing at him so he could see us easily, too. The other diver and I kept ascending as our computers indicated, and he stayed well below us. He was still well below us when we completed our 10 foot stops (on oxygen). We were right at our exit point (shore dive), and after waiting a while, we got out. We could hear his bubbles breaking the surface right next to us as we went about our business on shore, and we went back to watch on occasion. After 20 minutes, he came to the surface.

His explanation was that he was following his GUE training by doing his first stop at 3/4 of the maximum depth, followed by a series of stops every 10 feet thereafter. At some point he had reached the depth where his computer said he should be. He followed the computer from then on except for the 70 foot stop and the 60 foot stop. He had switched to EANx 50 at 70 feet, and he had stayed at those two stops longer than the computer called for to take advantage of "the oxygen window." With all that added deep time and his oxygen window stops, the Shearwater had added a total of 20 minutes of deco to his dive.

His explanation was that he had been trained to do his stops starting at 3/4 of his depth, and by golly there was no way he was going to do anything as crazy as going right to 60 feet. That was nuts! When I told him that the concept of the oxygen window had been dropped by GUE and others years ago when they realized that the supposed scientific basis of it was bogus, he simply refused to believe it. He had been taught to extend the stops with the high oxygen partial pressure, and he was going to do what he had been trained to do.

My feeling was that if you are going to say that you are going to use Buhlmann, then use Buhlmann--don't turn it into some sort of decompression stew by adding two different systems of thought to it. I also think the added 20 minutes of deco the Buhlmann algorithm added to his dive indicates what that algorithm at least thinks of the effect of his addition of the deep stops. If he had followed our written plan (plus the deep stops and oxygen window stops) instead of the computer, he would have done relatively short shallow stops and been out of the water 20 minutes sooner--to what effect?????

 

[scubadada]

If you are padding the stops you are not diving DSAT. You are diving something you have made up which is probably more concervative than DSAT and so says nothing about how effective DSAT is.

OP, these 'deep strops' are essentially a type of safety stop. Mostly they force a diver to control their ascent rate by actually stopping. By and large they can be ignored and perhaps the computer will add a minute at the final stop. If you have done a 42m dive and you get a minute at 22m and two at 11m it is unlikely you will on gas significantly at those stops. If you do those stops, then you will not have done a 20m/minute ascent to the surface. Avoiding such a fast ascent is worth while in my opinion.

Deco is a game of dice. People do get bent doing 15m, 45 minute dives. The idea is to reduce the incidence to an acceptable level.

The NEDU study mentioned above, is about trading deep time for shallow time. That was a particular claim made that by doing stops deeper then you could do less time overall for the same time on the bottom. That is not the case with these deep safety stops which are about extra stops, just deeper than 6m.

I disagree, I dive DSAT. I use DSAT NDLs for my no stop diving. Many divers do a 5 minute safety stop rather than 3 minutes. The Shearwater computers have a set 3, 4, or 5 minute safety stop in rec mode as well as the adaptive setting. The adaptive setting gives a 3 minute SS unless the dive is greater than 100 feet or comes within 5 minutes deco, in which case, the SS is 5 minutes. My strategy is something like that, on the conservative side. Adding a deep stop to my rec dives would not be consistent with diving DSAT, it might even turn a no stop dive into a deco dive. I use standard ascent rates.

For deco diving, I follow and clear the computer deco stops. I don't think I would be faulted for adding a little extra time at 10-15 feet after clearing deco, again, on the conservative side.

My goal is to return to the surface safely, so far, so good.

Good diving, Craig