Deep safety stop question

[limeyx]

Isn't V-planner essentially pure Buehlmann, and therefore it runs you up shallow before you start deco? You'd have to have a signficant obligation before V-planner would come up with a deep stop.

It's more of a bubble model idea to stop deep. Running you up shallow and then holding you there longer is a way to push the gradient (imagine the pressure pushing nitrogen out of the body). Stopping deeper is done to control bubble formation.

At least that's how I conceptualize it simply. If I'm wrong about V-planner, forgive me. I don't own it.

I think you can "insert" a deep stop like a way point (i.e. say 100 for 30 and then 1 @ 50) to "force" a deep stop.

What good it's going to do (or not) though, I am not sure, since as you say Buhlman tends to want to bring you shallow -- does adding a deep stop to an algorithm that was maybe designed before deep stops were researched buy you anything?

But yes, for Buehlmann (if that's what v-planner is) then even with Gradient Factors, getting it to automatically give deep stops may be tricky.

 

[Jim Lapenta]

It depends on what you call deep. On a dive to 155 for 15 minutes that I did last monday v-planner called for 1st stop at 80 ft then 1 every 10 ft after. I don't have my slate in front of me now but it was 34 minutes of deco. Lynne, just did a quick check and a 130 ft dive for 10 minutes on 25% nitrox did not call for a stop until 20 ft. The ascent was very slow like 4 minutes was recommended but you may be right. Up til now I've only been using it to plan mix dives. But I'll run some other stuff just for stuff and giggles over the next couple days. You need to remember though that v-planner is highly customizeable. You can program it to put in deep stops as well as vary stop depths and whole lot of other stuff I've not gotten into. If you'd like send me a couple profiles and I'll run em with some variables. You can also set the level of conservatism. That may throw in deep stops at shorter times and shallower depths.

 

[TSandM]

I was actually just responding to nereas's statement that V-planner didn't require any deep stops on a recreational profile dive. I don't think any Buehlmann-based program will. Even Decoplanner doesn't ask for deep stops on recreational profiles -- You have to add them yourself as a kludge.

 

[battles2a5]

From what I understand, the latest V-planner is VPM-B (I could be wrong). But I think there is a difference between bubble-model deep stops and the "pyle" stops used in conjunction w/ Buhlman and other Haldane-based saturation models.

The bubble models focus on keeping bubble formation at the minimum which requires more stops that start deeper. So these are your model-based "deep stops" as dicated by deco software, etc.

The saturation models bring you up to a shallow depth quickly for your stops. Technically, your safety stops can be viewed as "treatment" because in deep dives you can surpass the critical gradient of the faster compartments and cause bubble formation. Because of this, Richard Pyle advocated the use of deep stops (known as pyle stops) at the 1/2 depth, then 1/2 to safety stop depth to allow the fast compartments to off-gas in deeper water to prevent the formation of bubbles.

So people tend to use Pyle stops in conjunction w/ deep dives where an extra margin of safety is wanted outside of the model (I usually do it for anything over 100')

**Disclaimer- I am very new to decompression theory so I may be completely off base. I'd look to a more experienced tech guy to either confirm this or expose me for the imposter that I am.

 

[Steve R]

It depends on what you call deep. On a dive to 155 for 15 minutes that I did last monday v-planner called for 1st stop at 80 ft then 1 every 10 ft after. I don't have my slate in front of me now but it was 34 minutes of deco.

Geez Jim, that's a wack-load of deco for a 15 minute bounce dive!

Are ya sure you don't mean that the 34mins was your TRT? :14:

You'll find for your deco diving Jim, that your first "deep stop" will be roughly 80ft shallower than your max depth. Of course ascent speed will swing that a bit, but I choose to believe that we're all practicing something reasonable in that department....but I've been proven wrong before


Lynne: http://www.hhssoftware.com/v-planner/vpmdetail.html


EDIT:

It took me a bit, but I found another article from Ross that is worth the read WRT this topic.

http://www.hhssoftware.com/v-planner/decomyths.html

.

 

[SparticleBrane]

I'm going to point out that deco is not an exact science. Different agencies and organizations will say different things.

 

[Jim Lapenta]

Geez Jim, that's a wack-load of deco for a 15 minute bounce dive!

Are ya sure you don't mean that the 34mins was your TRT? :14:

You'll find for your deco diving Jim, that your first "deep stop" will be roughly 80ft shallower than your max depth. Of course ascent speed will swing that a bit, but I choose to believe that we're all practicing something reasonable in that department....but I've been proven wrong before


Lynne: http://www.hhssoftware.com/v-planner/vpmdetail.html


EDIT:

It took me a bit, but I found another article from Ross that is worth the read WRT this topic.

http://www.hhssoftware.com/v-planner/decomyths.html

.

Actually it was not a bounce dive. 2 minute descent and 13 minutes on the wreck at avg depth of 153. 21/26 trimix. Circled the entire boat(3 masted schooner down in 1870), sits so level and upright that the entire deck runs from 151-155 all the way around. We hit the upline at 15 on the dot. Total run time was 49 minutes. Deco on back gas. NAUI RGBM tables called for nearly the same deco schedule. A bounce dive to any depth is not worth doing. Since getting my heliotrox cert I won't do anymore deep Lake Erie dives (in excess of 100 ft) unless it's on mix. The clarity of my head with a little helium in the mix makes the xtra cost worth it.

 

[Steve R]

I guess our ideas of "bounce" varies.

15min is a bounce, but my misunderstanding of the deco was the fact that you didn't carry any deco gas....

assumptions assumptions huh?...lol.

Who on earth taught you to do dives like that with no deco gas anyway? Just wondering about the general thought process here.

Yes I know you did the St James I would have been there if I could have

 

[ianr33]

V-Planner is and always has been VPM. (of slightly different flavors)

If it is not giving any deep stops it is because it is not a deco profile.V-Planner is a great tool for doing sanity checks on recreational dives IF you know what you are doing with it,but dont expect it to give deep stops (or any stops at all!) on NDL dives.

As regards deep stops on recreational dives I dont think exactly how you do them really matters,but it is absolutley a good idea to do something.
I minute at half max depth,2 minutes at max depth minus 60,one minute at 50,40,30,20 then 3 at 10,really does not matter. What does matter is that you stop,or pause,your ascent deep and do a slow ascent to the safety stop.

The more I learn about deco the more I realise that there is no black/white, deco/no deco line but rather a huge gray area.
Can you subtract the deep stop time from the safety stop time? Sure! Its all guesstimates anyway. Want to stack the odds a bit more in your favor then do the deep stops AND a long safety stop

 

[Steve R]

The more I learn about deco the more I realise that there is no black/white, deco/no deco line but rather a huge gray area.

Who was it here that has given his account of what performing a deco profile is like?

You measure it with a vernier, mark it with chalk, and cut it with an axe? (Or something like that anyway). That's a bit of a running joke my buddy and I have, as we agree with it entirely, and trust me, some of our profiles have proved that out. <blush>

Knowing that to be true however doesn't excuse simply stupid profiles, which do happen a lot.

It generally revolves around an overly unwarranted fear of getting bent, which causes some divers to spend an enormous amount of time doing deco, and which it is arguable that the cure is possibly as bad as the affliction.

I should add as well for Jim's sake, if I had a gun to my head and was forced to do a dive like that with no deco gas I would limit it to 15mins BT myself! shatt!

Mind you, I generally look at deco as a penalty, not a badge to wear proudly. (Which is why I guess I don't plan to deco on backgas for nuthin' at these depths, and wondered why anyone would choose to do it).