deep stops or not

[TSandM]

As Doppler is saying, it is clear that the algorithm your dive computer is using to calculate your no-deco status is unhappy with the time you are spending deeper. Some are; some will give credit for the compartments which are offgassing during deeper stops. A lot also depends on the ascent rate you use to GET to the deeper stops; many people go much slower than they think they do, and if you review Marroni's papers on ascent strategy, a very slow ascent from the bottom was one of the worst for bubble generation.

But the bottom line is that, when you use a particular model, you need to comply with the assumptions and constraints of the model. You are using a brain-derived adjustment to your ascent strategy that is not compatible with the computer you are using. Change your ascent strategy, or change your computer.

 

[dmainou]

As Doppler is saying, it is clear that the algorithm your dive computer is using to calculate your no-deco status is unhappy with the time you are spending deeper. Some are; some will give credit for the compartments which are offgassing during deeper stops. A lot also depends on the ascent rate you use to GET to the deeper stops; many people go much slower than they think they do, and if you review Marroni's papers on ascent strategy, a very slow ascent from the bottom was one of the worst for bubble generation.

But the bottom line is that, when you use a particular model, you need to comply with the assumptions and constraints of the model. You are using a brain-derived adjustment to your ascent strategy that is not compatible with the computer you are using. Change your ascent strategy, or change your computer.

I'm sure most computers will give you credit for the off gassing of the fast compartments. However, you are still in gassing the slow compartments.

Go back to one of the posts I put before there is a new chat published that shows the situation clearly. A little extra time at the bottom has a big penalty at the top.

The chart is for a ccr simulation.

In principle, you can expect the same behaviour for your dive. But if you are only diving NDL... just follow your computer.

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[TSandM]

Computers used by technical divers generally have algorithms that consider the offgassing in the fast compartments. Some of the algorithms in the recreational computers (eg. Suunto) do not seem to . . . unlike other computers, you don't generate a great deal more no-deco time on ascent, and any extra time spent below safety stop depth counts against you.

 

[dmainou]

My very first computer, a suunto companion seemed to be just an electronic square profile dive table, however, every other computer I've had seems to calculate multilevel dives. Youz are right in that suunto requires a lot more time in the shallows to be able to get out of the water and therefore penalises more if you don't stop at the stop.

RGBM is an untested algorithm. Its only testing comes from it's users and the manufacturer only knows there was a problem if you care to report it after you landed in hospital. It really makes me wonder why would anyone like to be a guinea pig when there are manufacturers offering tested algorithms at exactly the same price or cheaper. I mean, to put it in context you can get a fully fledged tech computer with a colour screen for the price of the cheapest suunto. Bare in mind that the fact that it is ccr, trimix, and multi tank capable dos not prevent you from selecting only one tank and one gas (air).

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[100days-a-year]

It's all theory not fact so.... computers are mostly guestimating a solution using a guestimate of how the guestimate of a typical diver offgasses in a typical dive in typical conditions.There are outliers who get bent diving "safe"computers and others who dive far outside those parameters and are symptom free.

You have to ask yourself if the risk is real and if it's worth it.

I implemented 60' 1-2 min stops years ago on short dives and 2/3 max depth on mix dives.I wasn't bent before and haven't been since.No harm,no foul and I "feel" safer.

 

[dmainou]

Hmmmm kind of. Her Drs Buhlman and Haldane had the benefit of thousands of manned dives in controlled environments. The rgbm guys at least have a biased database of events. 100days-a-year model of mood driven stops has a small sample of dives within a population of one. You may or may not be bent after your dives. Who knows. The fact that you don't have clinical symptoms doesn't mean your model is ok even if you feel safer

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[halocline]

As far as my very basic understanding goes, the issue with deep stops for recreational diving is that the controlling compartments are often the faster ones in NDL diving, which means the best way to off gas would be to get to the safety stop quickly and spend more time there. I think of NDL diving as more of a gradient than a hard line between NDL and required stops; so having a look at the general requirements on the deco side of the NDL 'boundary' is a good guide for dive behavior on the no-deco side of that boundary. IOW, what would a model tell a diver to do if the planned profile was 'slightly' into required stops; the initial ceilings are typically shallow. So a nice long shallow stop works well within NDL. The slower compartments have a lower pressure threshold and thus need deeper stops, but those compartments are more likely controlling within a technical dive profile.

The best advice given in this thread IMO was to study basic deco theory, enough to get an idea of how tissue compartments work, and then it becomes fairly intuitive that shallow stops are best for most recreational divers. In fact I rarely pay attention to my computer's NDL number; I'm much more interested in the N2 loading bar graph. When I get more involved in deco diving study I'd like to see computers or software that display the loading of multiple compartments over a specific profile. I think it would be interesting to be able to graphically see the progressive loading and off gassing of several compartments in real time during a dive (or simulation). That would be for study purposes; while I'm actually diving for fun I have no interest in staring at a computer screen any more than is necessary.

 

[dmainou]

Then you want to buy a Henrichs Weikamp OSTC 2c. You can chart al compartments for nitrogen and helium both in and out of the water.

The most telling thing about those arbitrary deep stops will be on multi day diving where the slow compartments keep creeping up vs a diver following the model and heading directly to the required stop (safety stop or surface). I suspect that as dives accumulate deco will trigger singer and sooner. The fear is that the ndl computer may be asking for you little deco as it can't handle properly the mood driven deep stop and you end with a so called undeserved hit

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[Ayisha]

I'm wondering what the difference is between planning a multi-level dive and planning a deep stop?

FWIW, I plan my deep stop at 50 feet for 1 minute, no matter how deep I go (recreationally).

 

[Doppler]

I'm wondering what the difference is between planning a multi-level dive and planning a deep stop?

FWIW, I plan my deep stop at 50 feet for 1 minute, no matter how deep I go (recreationally).

Each successive level on a multi-level dive is above the off-gassing ceiling of the previous depth... In a true multi-level dive.


you are doing it wrong! Your "deep" stops are arbitrary... Stop doing that.