What computers are you using for tech dives?

[tbone1004]

There are multiple compartments with different half times and different constants, the off gas and on gas tracking are not symmetrical. So the estimate of gas loading will be different between the Suunto and any GF values you pick. Thus the limits are very likely to be in different compartments and be reached differently in different profiles.

You are used to the simple scaling of limits and the two GF numbers controlling that.

It is a loosing game to try to fit a these two curves with just two variables being scaled.

buhlmann uses more compartments than Suunto does *16 vs 9 iirc*, the difference is how wonky they made that algorithm by trying to add in weird variables to make it look like a bubble model.
I can tell you that while I may not have a problem with their 160ft dive profile, I have huge problems with it on the 250+ft profiles because it puts in a very shallow ascent curve with the deep stops and then kicks me out of the water with more total inert gas loading. You just contradicted yourself by saying that they come out very similar, well the fact is they don't come out similar at all. If by your words they were "very similar" then you would be able to choose a GF setting that would closely approximate the ascent curve. You just said above that you can't do that, so how are they "very similar"

 

[KenGordon]

You chose a GF to match for each case. With the GF computers you can do play that game and try to match any given curve. However one GF will not match a computer using different m values, and especially not one using asymmetrical on/off gas.

By similar, I mean that whenever I dive with a Helo2 buddy the deco is all over at about the same time. Plus or minus a couple of minutes. I know that actual dives are outside the scope of SB but now and again they interfere with our ability to post and we can pick up some data points.

If you do a 170 ft 30 minute dive with the Suunto on P0 you get a 166 minute run time with a profile that is shallower than the NEDU shallow stops profile for everything other than a minute at 30m and a couple at 21m. Indeed the 3m stops are only a minute different. Compare that with the deep NEDU profile which had tens of minutes deep.

So my point is that a Helo2 is not a deep stop computer. The NEDU study is not telling you anything much about the Suunto profiles, like it doesn't tell you much about particular GF pairs other than don't go mad with staying deep for ages.

If you think that the 250ft dive is too aggressive on P-2 then set it aggressively. But how do you know what a 250ft dive deco profile should look like?

Clearly the Suunto marketing people backed the wrong horse, but if you look past the marketing at how stuff actually behaves you will find a perfectly fine computer that will let divers do the dives they want to do.

I am assuming the Mares is similar. I don't know that because I have never used one. The Suuntos and Shearwaters I own and dive.

 

[100days-a-year]

An EDGE or BTs and tables.Repeatedly.

 

[scubadada]

Interesting comments. I have said before, DSAT and Buhlmann ZH-L16C do not track well. I believe this is related to different slopes of the M-value line. DSAT is more liberal at deeper depths while ZHL is more liberal at shallow depths. This seems to be somewhat more at higher nitrox percentages. I'm still running DSAT and Buhlmann in parallel to gain more experience. Currently, I run Buhlmann at a GF hi of between 100 for deep dives to 90 for shallow dives. Seems like others may have similar, complimentary data

 

[EFX]

Have there been any actual dive studies for algorithms utilizing bubble models that confirm or deny their validity for diver safety? Don't point me to the NEDU study because it used deep stop profiles completely different than VPM using the same dive profile.

 

[KenGordon]

Have there been any actual dive studies for algorithms utilizing bubble models that confirm or deny their validity for diver safety? Don't point me to the NEDU study because it used deep stop profiles completely different than VPM using the same dive profile.

Although the NEDU study did not address this directly, analysis of the results and in particular surfacing nitrogen loading suggests you are better off shallower sooner to avoid picking up more nitrogen during the deeper stops. Of course it is a question of degree, come shallow too fast and you risk the fast tissues.

Simon Mitchell argues that it is not the case that VPM and BVM are completely different, given a high conservatism VPM profile looks like the deep stop profile in the NEDU study.

There are some references in here https://www.bsac.com/core/core_picker/download.asp?id=24727&filetitle=Prof and probably lots more in the various deeps stops threads here, rebreather world and elsewhere.

 

[Capt Jim Wyatt]

If Simon says it you can take it to the bank.

 

[Cyborg Pirate]

Ok, lots of good comments and opinions. Here is kinda where I stand.... I am taking the intro to tech course. I have purchased my doubles wing and currently setting up my atomic M1's for doubles. Yes I have computer nitrox diver;however yet to take advanced nitrox and deco. I want to get into diving doubles and extending some bottom time. Honestly after doing a long self assessment of my diving goals..... I am a long ways off from getting to trimix (just found out I'm gonna be a dad hence the long few days since I chimed in) So a nice long slow period of getting good at skills with doubles is how things are gonna go if I ever get into trimix. So that being said.... icon and tables for a bit. Then at least one perdix. Hoping for 2 by this time next year???? Any other tips on equip I am gonna need for diving doubles and getting good at them before stepping too far into tech?

 

[KenGordon]

The fashionable thing on here is to do AN/DP and then dive a twinset with a deco stage. That is a very big jump from typical single cylinder NDL diving and a fair old jump from NDL twinset diving.

You can do lots of interesting stuff which is relatively shallow and so doable with 32% backgas and moderate back gas deco. This is less complicated and avoids the whole problem of breathing the wrong gas.

Find a buddy with similar goals. For dives which need non trivial training getting buddies can be a barrier to actually diving.

Understand planning properly.

Pressure on time and finances having a child make diving a secondary concern. Also it may not be appropriate to be doing higher risk diving given the addition consequences of leaving a child to never know it's father. Keeping in practice is harder with less time and practice is important. On the other hand having something for yourself can be a boon when the world seems to resolve about nappies and childcare.

I lost three divers from a week long trip last year due these sorts of issues, and there are several more in our club we see much less after children. The diving will largely still be there when they are older.

 

[Cyborg Pirate]

The plus side.... I captain on a dive boat. It's a lake dive charter but it's diving nonetheless. It's a great side job for me and gets me lots of dive time. Which is why I feel it a good chance to get into doubles and get comfortable with them. Yes AN/DP are definitely on the list of classes in the near future. I am hoping within the next 6-8 months. Our lake does have some nice deep and overhead diving in it. So when the time comes it will lend itself useful for tech diving and training. I solo dive now quite often. (I also live on the lake). So yes planning and redundancy is something I am very used to, and always willing to learn more. My primary job is a high stress and risky job so diving actually is my getaway....