Which deco stop to skip?

[Nirvana]

Do you really have data to represent that violation of required deco stops won't cause "issues" with a dive computer?

I cannot make broad statements about dive computers but, as far as I know, the Shearwater Petrel, currently featured in advertisements on this board, would be an example. Also, the Mare Icon HD will let you skip the "deep stops" (but not the deco stops) it sets without considering it a violation.

 

[dumpsterDiver]

I cannot make broad statements about dive computers but, as far as I know, the Shearwater Petrel, currently featured in advertisements on this board, would be an example. Also, the Mare Icon HD will let you skip the "deep stops" (but not the deco stops) it sets without considering it a violation.

we are talking about required decompression stops, not optional, elective deep stops... I thought that was pretty clear in the context..

If you are contemplating blowing off required deco stops, who is worried about optional stops that are deep? yes?

 

[Nirvana]

we are talking about required decompression stops, not optional, elective deep stops... I thought that was pretty clear in the context..

If you are contemplating blowing off required deco stops, who is worried about optional stops that are deep? yes?

There is no need to be aggressive, specially when you seem to be not too interested in what I wrote.

I specifically spoke about the Shearwater Petrel first because it is my understanding that if the diver doesn't complete a certain stop, it will compensate on the next one. Perhaps you could have better spent your time researching it instead of berating me for giving you information you did not want.

As for the Mares Icon, I cited it because it will give the diver deep stops and deco stops on the same deco schedule, what shows the computer algorithm assumes they will play a relevant part (I don't think Mares would just suggest a diver makes a relaxation stop in the middle of a half-hour decompression schedule).

 

[boulderjohn]

Abandoning a deco plan does not indicate surfacing. It indicate changing the deco approach/new plan; the old one is not going to work. Example: abandoning vpm plan because you dont have the deep gas does not mean SURFACE!! It means new approach, screw the deep stuff I have no gas, get shallow so I can use what I have. In this discussion we debate what to skip based on limited gasses/health issues or the likes, "get out before the cake is ready". If you have no gas, drown or surface.

OK, then. Let me ask the question YET AGAIN. It sounds to me like you are describing amending the plan. How is abanfoning the plan (BAD!) different from amending the plan (GOOD!)? I am just thoroughly baffled by how you folks are using the English Language. I know I was not as diligent as I should have been in my Ph.D studies in English, so I have to bow to your superior command of the English language as you cudgel me for my lack of understanding.

---------- Post added April 25th, 2013 at 06:35 PM ----------

Are you sure this works with an dive computer? You can VIOLATE the computer, blow off the required deep stops and then all computers will happily go along with it and recalculate your adjusted deco plan after a violation? I find that hard to believe.

No, not all computers will do this, but many will. The Shearwaters will.

The fact that you don't know much about this does not mean it is not true.

 

[DevonDiver]

What is the difference between abandoning and amending?

I think Ajduplessis explained it. I didn't intend it to be sarcastic.

I'm assuming most of us dive with a 'modern' algorithm. Those tend to feature in all of the deco software currently available. Algorithms which stop you deep to prevent initial bubble growth and/or collapse bubbles before they can grow on ascent. Those deep stops have a purpose - and that purpose reflects in the calculation of later (shallow) stops. Whilst the ascent may be governed by user selected gradient factors, the shallow stops are likely to be shorter with a model that has accounted for bubble dynamics at depth.

Abandoning that model means discarding the deep stops that underpin the theory/algorithm used to calculate the deco obligation. Ascending directly to shallow stops (not to the surface... don't know where people got that from?!?) is a shift in model. That is Haldanian thinking... a Haldanian model. Get shallow, hang long. Some computers may cope with that shift, others may not.

Amending the model would mean retaining 'faith' in the implications of bubble reduction at depth... and the consequent impact that has on the ascent curve and , in particular, the shallower stops. It'd mean a more aggressive ascent profile, but the 'curve' would be maintained. For instance, a change in gradient factors to speed ascent - but with all calculated stops still being carried out.

I just find it somewhat ironic that people would plan every dive with a bubble model, conduct ever dive with a bubble model.... but then abandon it and switch to an ad-hoc Haldanian model when the s%*t hits the fan.

There are some reasons why you'd do this, for instance; losing back-gas and carrying ample 100%. But otherwise, why opt for such a drastic change in approach simply because an amendment to the deco plan is necessary?

---------- Post added April 26th, 2013 at 09:03 AM ----------

lBut that is not what Andy (DevonDiver) seemed to be saying. He seemed to me to be saying that what I suggested (shaving time off the deep stops and adding time to the shallow stops to make it more in keeping with a Bühlmann algorithm) is abandoning the plan, and he things that is wrong.

John, just for clarification - I don't think it's wrong. I was just confirming whether that was, indeed, the approach being put forward.. and raising the question of why a Haldanian/Buhlmann ascent would be preferable to a modified bubble-model ascent (i.e. VPM-B).

What was on my mind was the question of whether such actions represent an inclination towards 'tried and tested' (an ultimate distrust in bubble models) or whether there was some other rationale towards such a major shift in approach.

 

[boulderjohn]

Am I right then, Andy, in assuming you think that people should choose one model and cling to it tightly, declaring all other models as he work of Satan and a sure path to painful death? Or is it possible that some people might look at the research and see that there is no clear evidence that either approach is wrong, observe that people who are following all the different approaches to deco seem to be doing just fine for the most part, and deem it OK to use a different proven approach under difficult circumstances?

 

[DevonDiver]

John... please.... don't read more into my questions than the questions...

(for the record, I still sometimes use Gurr's Pro-Dive Planner, circa 1994... it's so old I have to run an MS-DOS emulator on Windows. LOL. I 'grew up' diving that and it never failed me. No 'devil' there..)

 

[Nirvana]

BoulderJohn,

I don't mean to intrude in the discussion you and DevonDiver are carrying, specially since you both most certainly have much greater knowledge than I do. However, it is my impression you may be accidentally misinterpreting what he said.

He is saying that most divers plan their dives with models that take into account bubble growth at depth and therefore establish stops that are relatively deep. In this scenario, he would consider that in the case of an emergency, one should try to keep the general approach of the model, shortening but not completely abandoning these deep stops.

He finds it strange that someone might decide to entirely cut the deep phase of decompression and go directly to the shallow stops, approaching a Haldanian model, and got the impression this is what you were proposing.

Finally, I don't mean to imply you need an interpreter, DevonDiver, and I am sorry if I misrepresented what you said.

 

[boulderjohn]

BoulderJohn,

I don't mean to intrude in the discussion you and DevonDiver are carrying, specially since you both most certainly have much greater knowledge than I do. However, it is my impression you may be accidentally misinterpreting what he said.

He is saying that most divers plan their dives with models that take into account bubble growth at depth and therefore establish stops that are relatively deep. In this scenario, he would consider that in the case of an emergency, one should try to keep the general approach of the model, shortening but not completely abandoning these deep stops.

He finds it strange that someone might decide to entirely cut the deep phase of decompression and go directly to the shallow stops, approaching a Haldanian model, and got the impression this is what you were proposing.

Finally, I don't mean to imply you need an interpreter, DevonDiver, and I am sorry if I misrepresented what you said.

I understand the issue.

he problem is that people who see it as "bubble model" vs. "Haldanian" are missing something important.

The bubble model does not discount the Haldanian approach. It is not one against the other. Bubble models accept that the Haldanian theory--modified by later theorists like Workman and Bühlmann--is also true. many people therefore more accurately refer to the "bubble model" as "dual phase," meaning that we have to use a balanced approach that deals with nitrogen in both phases--dissolved and free gas. Thus, shifting the emphasis from bubble control to dissolved gas control is really not an abandonment of one theory for another. It is exactly what I suggested--merely a shift in emphasis.

 

[DevonDiver]

The bubble model does not discount the Haldanian approach. It is not one against the other. Bubble models accept that the Haldanian theory--modified by later theorists like Workman and Bühlmann--is also true. many people therefore more accurately refer to the "bubble model" as "dual phase," meaning that we have to use a balanced approach that deals with nitrogen in both phases--dissolved and free gas. Thus, shifting the emphasis from bubble control to dissolved gas control is really not an abandonment of one theory for another. It is exactly what I suggested--merely a shift in emphasis.

So...

1) If bubble model contains Haldanian...

2) ...and dissolved gas...

3) ...and you remove the dissolved gas element...

4)... you get what?

Crass analogy: I got a can of franks and beans. I remove all the franks. Now I've got a can of beans...

Did I amend the franks and beans.... or did I abandon the franks? What am I actually eating? Franks and beans...or just beans?