What computers are you using for tech dives?

[KenGordon]

Set the Helo2 to p-2

Similar is when you only have to wait 2 minutes for the bloke on 45/80 to clear after the Suunto.

Btw, earlier you beat the Mares and Suunto with The RGBM as deep stops stick.this Suunto profile looks to be less deep stoppy than the GF profiles. So do you agree it is likely a safer profile?

Also being less deep stoppy a different choice of gas might be better.

 

[ahereng]

When I used my Helo2 for deco-diving, I used p-2 in order to be the least conservative. The people I know that also dove the Helo2 did the same, as it would give a lot of deco if left in P0 as shown above. When it was in -2 it was fairly similar to my Petrel(which I bought later and used the Helo2 as backup).
The Helo2 would typically get you as fast as possible to 3m, and then stay there for a long time. I usually waited till both computers cleared before I surfaced.
When I started using the Petrel(gf 30/70 as standard) the Helo2 would typically be a little more liberal in the relatively shallow tech-dives, but added a little more deco on the deeper dives.

 

[tbone1004]

@KenGordon I was surprised it was as shallow as it was. Note that the total times are including ascent times so are the total dive time minus the bottom time.
What is bizarre is that to get a profile somewhat similar to Buhlmann, you have to flip it over to something like 80/60 to get it to behave somewhat similar with deepstops off. Deepstops off doesn't really make sense to how RGBM would be implemented with that shallow of a profile because of how the bubble model works. Something really bizarre is going on in there and while I don't object to the ascent curve that it shows on -2 with deepstops off, the fact that I don't know the why and how behind the what is enough for me to steer clear of it

p-2 still yields
70-1
30-7
20-9
10-24
total 46

on 100%
40-2
30-12
20-7
10-27
total 48

on 80%
40-2
30-6
20-7
10-20
total 41

 

[KenGordon]

You should leave the deep stops on. It is not quite optional on a helo2.

Fear of the unknown? I have done lots of deco dives with Suuntos, I usually have a buddy with a Suunto on a deco dive.

My view is that the 'RGBM' bit is marketing and that they are really dissolved gas modes with mods for Pyle stops, shorts surface intervals and repeat diving.

On the other hand there are GF computers with unknown helium M values, unknown means to set the first stop depth and only the simplest symmetrical gas take up and off gassing rules. So plenty of unknowns there too.

You get used to what you use and see used. The typical entry level club diver here gets a Suunto. Once they start doing deco dives they carry on using the Suunto. If people move on to accelerated deco or trimix they might get something else, but at the start (and actually for a long time) the computers that SBers slate as 'recreational' are perfectly adequate.

 

[Doby45]

It would seem that the OPs original question was

What computers are you using for tech dives?

@KenGordon seems to have an issue with people simply answering that question. The #1 computer in the technical diving arena is a Shearwater, period. Can and do other computers works too, sure they do. But if the OP is asking people what computers they use and they say Shearwater and then they also recommend Shearwater why is this pushing a burr under your saddle?

 

[KenGordon]

When I used my Helo2 for deco-diving, I used p-2 in order to be the least conservative. The people I know that also dove the Helo2 did the same, as it would give a lot of deco if left in P0 as shown above. When it was in -2 it was fairly similar to my Petrel(which I bought later and used the Helo2 as backup).
The Helo2 would typically get you as fast as possible to 3m, and then stay there for a long time. I usually waited till both computers cleared before I surfaced.
When I started using the Petrel(gf 30/70 as standard) the Helo2 would typically be a little more liberal in the relatively shallow tech-dives, but added a little more deco on the deeper dives.

This is my experience. I gave up using 30/70 when I found when diving with a buddy on 32% I had more stops when I was diving a rebreather.

 

[tbone1004]

You should leave the deep stops on. It is not quite optional on a helo2.

Fear of the unknown? I have done lots of deco dives with Suuntos, I usually have a buddy with a Suunto on a deco dive.

My view is that the 'RGBM' bit is marketing and that they are really dissolved gas modes with mods for Pyle stops, shorts surface intervals and repeat diving.

On the other hand there are GF computers with unknown helium M values, unknown means to set the first stop depth and only the simplest symmetrical gas take up and off gassing rules. So plenty of unknowns there too.

You get used to what you use and see used. The typical entry level club diver here gets a Suunto. Once they start doing deco dives they carry on using the Suunto. If people move on to accelerated deco or trimix they might get something else, but at the start (and actually for a long time) the computers that SBers slate as 'recreational' are perfectly adequate.

putting deep stops back on makes it really bad
with deep stops on -2
100-1
70-2
50-2
30-4
20-9
10-25
total of 50 minutes. 6 minutes longer than 30/70 running the same dive plan and gases. Again, in this case it isn't the ascent curve that I really have an issue with, it's the fact that you have literally no idea why the computer is making the decisions it is making, especially when the computer manual tells you it lowers M-values arbitrarily and that the diver doesn't need to know or worry about it. WTF?!?
Shearwater publishes what they do for helium, there are no real unknowns about that computer in terms of the how and why behind the what, very much unlike Suunto where they literally tell you the equivalent of "just trust me, I know what I'm doing". Others running Buhlmann may be different, but I don't think anyone has advocated for one of those yet...

 

[KenGordon]

It would seem that the OPs original question was

What computers are you using for tech dives?

@KenGordon seems to have an issue with people simply answering that question. The #1 computer in the technical diving arena is a Shearwater, period. Can and do other computers works too, sure they do. But if the OP is asking people what computers they use and they say Shearwater and then they also recommend Shearwater why is this pushing a burr under your saddle?

Your Icon HD has a wonky algorithm on it by most peoples opinions.

The icon is a great computer for ... recreational diving only.

Mares and Cressi also make computers that could be used for technical diving but they use RGBM. Recent research indicates that RGBM isn't the most efficient algorithm for decompression and generally calculates shallow stops (the really important ones) that are too short for staged decompression diving.

goes against the state of the art in decompression research,

RGBM algorithm is what is not backed by current research.

These are not recommendations. They are saying that the OP has a bad computer already and that similar computers are bad.

Sure say buy a Perdix because it has a nice screen and a bunch of positives, but slagging off the competitors for bogus reasons is not helpful to anyone.

The arguements above claim that the Suunto etc are dangerous because of excessively deep stops and insufficient shallow but also claim that they are too conservative and have too much deco. Doublespeak!

 

[tbone1004]

@KenGordon

to explain my part of what you quoted
Suunto uses a Haldanean model with 9 compartments which is what Buhlmann evolved from, then has a bunch of modifications to it as you alluded to in order to mimic a true RGBM algorithm. This is wonky because it doesn't tell you how or why it does what it does and you are expected to go on a "trust me" dive with this computer.
Mares uses the same sort of haldanean modified to rgbm.
They do this because they don't have the processing power to actually run full RGBM which is very intense from a computing perspective.

RGBM goes against the state of the art with current decompression research as a foundation for decompression profiles. Whether or not these psuedo RGBM algorithms produce profiles that mimic appropriate ascent curves is one thing, but the foundation of them goes against current research.

If you want to go on a trust-me dive with your computer, especially when the manual straight up says that it will adjust m-values arbitrarily, not tell you what will cause it to adjust them, and then goes on to tell you that you don't need to worry about it, then fine, put your full trust in that computer. I don't want the computer messing with my deco profiles without telling me why.


I used an easy example of a relatively simple tech dive. Let's go to 250ft for 30 mins on 12/70. Use 35/25, 50%, and 100% as deco gases. 50-80 buhlmann, -2 Suunto Tech RGBM with deep stops on. GUE Deco planner and Suunto DM5 set to immediate descent. Buhlmann on left, Suunto on right. Buhlmann has 112 mins of deco, Suunto has 99. Suunto has 3 more minutes of deco before the 20ft O2 stop, and 13 less minutes of total deco. So there is proof of more deep stops and less total deco time on a dive where it matters. Closest approximation for this dive of the Suunto deco profile on Buhlmann is 50/100

180-0-1
140-2-2
130-2-0
120-2-2
110-2-1
100-2-2
90-3-3
80-4-4
70-4-3
60-5-4
50-6-7
40-9-14
30-15-16
20-19-16
10-37-24​

 

[Diver0001]

The arguements above claim that the Suunto etc are dangerous because of excessively deep stops and insufficient shallow but also claim that they are too conservative and have too much deco. Doublespeak!

I'm going to assume that you are not abreast of the latest research. Technical divers are pretty clear that bubble models (RGBM, VPM, etc) are not suitable for technical diving.

For recreational diving I dont' think it matters at all because differences in algorithms all happen in the "grey area" where the chances of a DCS incident was small to begin with....

However, this thread asks about technical diving and I think the OP has been well informed that bubble models are not ... optimal ... (read, not OK) for that context.

There is no doublespeak there. Do not use bubble models for technical diving. No doublespeak.

R.