What computers are you using for tech dives?

[100days-a-year]

I have no clue

-Tom from Suunto

 

[jeff h]

But according to BRW....

He seems to make very good recommendations. I did notice he uses extreme examples when describing elevated risks, ie like setting depth records on high helium mixtures and then switching to air or high nitrogen mixes, or the example of heliox type diving with nitrogen/air based decompression. In modern tech diving these extremes don’t normally exist. I suppose this does support the philosophy to dive trimix based gasses up to the 70ffw switch to 50%. In the past (15yrs ago) I used quite a bit of 32% and 36% nitrox for deeper stops, maybe this was a bad practice.

Summary of what I heard is pretty straight forward:

1. Keep the nitrogen fraction (or PPN2) close when making switches
2. Never switch from a high nitrogen based gas to heluim, this will cause an isobaric “slam”. You would really have to go out of your way to do this in tech diving. Most people save the helium for the deeper part of the dive
   
3. Air breaks can add risk if high helium mixed dives have been conducted at extreme exposures.

So there is minimal risk when using the typical recipes most people use for modern decompression diving above 275ffw. When planning deeper dives, then an intermediate trimix travel/deco gas would probably be smart.

As an example of a “bad idea”, an old school type diver once recommended to me that I bring an Al-80 of air to switch to above 200 feet on a deeper dive I didn’t take that advice, but if I did, then I would have switched from let’s say a 12/60 (28% nitrogen) mix to a 79% nitrogen with no helium.

In switching to CCR diving this pretty much goes out the window. When I did my deeper CCR dives I would just stay on my helium based diluent all the way up, adjusting/controlling only PPO2 (1.2 btm to 1.4 deco to 1.6 depending on exposure). I haven't dove in about six years, so my info may be dated.

 

[tbone1004]

@jeff h even on CCR it's relevant because you still have to have the appropriate bailout/deco mixes, so while it doesn't matter on the loop since you are constantly adjusting to depth, if you have to bailout you still need to plan the dive as if you were on OC

 

[jeff h]

@jeff h even on CCR it's relevant because you still have to have the appropriate bailout/deco mixes, so while it doesn't matter on the loop since you are constantly adjusting to depth, if you have to bailout you still need to plan the dive as if you were on OC

Excellent point.

 

[elgoog]

It this typical behavior in the US tec dive community that beginners or any divers, when they make mistakes, are bullied by more experienced ones, even trainers?

It is not. I'm not sure if you're genuinely asking or not-so-subtly implying but blanket statements like these are not going to do Suunto any favors. Maybe run what you're saying/posting here by your engineering as well as PR people in the future. For someone who claims to be associated with a major player in this industry, your attitude leaves a lot to be desired.

Could someone give me a reference to the non-proprietary source code or algorithm description of the Bühlmann GF used in any popular tech dive computer?

Why do you need the source code? The method (and probably even the math) behind it are published - someone else's code is not going to explain it any better to you.

 

[boulderjohn]

Unfortunately I made some wrong choices in words and did not look into details about the gas switch and as a result a lot of naive bullying and trolling starts to pick on unimportant details, blurring the actual topic.

Here is the problem with your original posts, the ones that led to the alleged bullying.

• Your signature says you are representing Suunto, thus implying an expert status.
• You said that the switch from 21/35 to EANx 50 was "suicidal" because of ICD. This is an incredibly common switch, with no known signs of anyone being hurt by it. It may, in fact, be the most common gas switch in technical diving. This creates a disconnect between what you said and your implied expert status.
• You later said "suicidal" was an unfortunate choice of words, an overstatement. Even if it is an overstatement, your statement still means that making that the gas switch is a serious mistake. You now say that the old RGBM helped make up for that mistake with prolonged deco times.
• Another post later linked to a video in which Bruce Weinke, the creator of RGBM, says in the clearest possible language, that gas switches to EANx 50 create no ICD problems whatsoever. Thus the creator of RGBM contradicts your statement about RGBM.

It this typical behavior in the US tec dive community that beginners or any divers, when they make mistakes, are bullied by more experienced ones, even trainers? Here in Europe divers are buddies, more experienced ones supporting the beginners.

This is the heart of the problem with this thread. Your first post did not have the tone of "I am a beginner trying to learn. Please help me." The implied message instead was "I am the expert from Suunto here to tell you why what you are doing is so very wrong." People on ScubaBoard will be very friendly and helpful when a beginner comes in looking for advice; they will not be so friendly and helpful when someone who claims to be an expert makes bold assertions that are incredibly wrong.

 

[KenGordon]

Why do you need the source code? The method (and probably even the math) behind it are published - someone else's code is not going to explain it any better to you.

The published work is for cutting tables, not for a dive computer. For a dive computer there are issues that need the be solved which are up to the implementer.

 

[elgoog]

The published work is for cutting tables, not for a dive computer. For a dive computer there are issues that need the be solved which are up to the implementer.

Thanks for the clarification on tables vs computer - I stand corrected.

If there are issues implementing this on a computer, then it seems like there will never be a non-proprietary algorithm or code to implement it, right? Not in the sense that they are obfuscating what is being modeled but the how behind it.

 

[KenGordon]

There is the OSTC implementation which turns up in Subsurface, but we can only guess about the others.

 

[elmo]

There is the OSTC implementation which turns up in Subsurface, but we can only guess about the others.

We can do a bit better than just guess. We can download dives from real computers running Buhlmann GF and compare the dive computer reported ceiling (and NDL and TTS) with that calculated by Subsurface when set to use the same gradient factors. I don't want to get involved in my-brand-of-dive-computer-is-better-than-yours, but for the record, the ceiling calculated by my Shearwater closely matches that calculated by Subsurface. It's not exactly the same but it's close for the dives I've done.