What computers are you using for tech dives?

[KenGordon]

@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​

So now it is too aggressive? Maybe all those DSAT supporters arguements about how you can make an aggressive computer less aggressive but not a conservative one more aggressive should be wheeled out.

I agree that between now and doing an 75m dive the OP ought too get a handle on dive plans to put on a slate and take advice about what is reasonable. By then a Perdix might be an appropriate tool, but he has some way to travel before then and plenty he can do before spending that money.

The manual for the Helo2 describes the factors which modify the M values. It also describes the asymmetrical on-off gassing behaviour and gives at least the half times of the compartments. Basically it is the same as a Buhlmann computer and not at all like a bubble model computer. It has some of the features of other models, such as off gassing more slowly than on gassing.

The proof is in the diving.

 

[KenGordon]

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.

Suunto Tech RGBM is not the same as RGBM. It is a dissolved gas model. It has M values, not critical bubble radii. Take a read of the Helo2 manual. They spread the info out in an unhelpful way but it is there.

It inserts fake deep stops which can be ignored.

When I am at home I might run the NEDU dives on DM5 to see where it lies on the spectrum.

 

[tbone1004]

@KenGordon the concern is how with the exact same settings the computer goes from something like 80/60 to 50/100. It is not a predictable algorithm. If you believe in it, fine, but in their own dive planner, it is doing some very strange stuff that makes no sense

 

[PfcAJ]

Suunto Tech RGBM is not the same as RGBM. It is a dissolved gas model.

Wat?

 

[Diver0001]

Suunto Tech RGBM is not the same as RGBM. It is a dissolved gas model. It has M values, not critical bubble radii. Take a read of the Helo2 manual. They spread the info out in an unhelpful way but it is there.

It inserts fake deep stops which can be ignored.

When I am at home I might run the NEDU dives on DM5 to see where it lies on the spectrum.

Yeah, that's what we used to call "bubble wrapped Buhlmann". The simple truth, however, is that even if you can deduce some of the workings of the algorithm, Suunto's model is proprietary and it not available for scrutiny. This alone disqualifies it for me as a suitable algorithm for technical diving.

R..

 

[sunnyboy]

To answer the OP, Shearwater Predator on my right wrist, and OMS bottom timer on my left arm up near the dump valve.

I'd also say, as a tech diver, why wouldn't you have a shearwater? IMO they are simply the best dive computer available and the service is the best anywhere.

 

[Ioannis]

Any thoughts on the Ratio ix3m tech+ guys? Have anyone of you tried it?

 

[tbone1004]

Any thoughts on the Ratio ix3m tech+ guys? Have anyone of you tried it?

I've taken it on a test dive. I couldn't find the Tech+ on anyones website in the US, but the Deep which doesn't support CCR mode is $1k on Amazon right now. The Reb which is $1400 but has the sensor board so similar to the Petrel EXT. I assume the Tech+ is somewhere in the middle. You want the Tech+ though because the Deep only has preset algorithm adjustments
anyway, point is it is more expensive than the Perdix for mostly similar functionality. It has some extra sensors, but I'm not entirely sure they're particularly useful.
I do like the vibe alarms in theory though wouldn't pay more for it.
I do like the "home" button as the Shearwater menus can get a bit tiring to scroll through, but again not something I want to pay more for.
I prefer the piezo button on the Shearwater
I like that they have an O2 analyzer that can be integrated, though if you have a Petrel EXT you could make one yourself
I don't like the proprietary USB recharge cable. I have no issues with rechargeable batteries in computers, but if you have one, please use a standard USB cable for it like Dive Rite did on the Nitek so I don't have to worry about it getting lost/stolen/broken on a dive trip.

If I was in a place where I was diving daily and it was nice and warm, I would consider getting something like the iDive Avantgarde to use as a daily use computer, but that would only be convenience of replacing my watch. If I'm doing drysuit diving, or not diving day in and day out, then it wouldn't be on the radar. The big ix3m wouldn't be on the radar against the Shearwater for reasons listed above

 

[KenGordon]

Wat?

Yes. Read the manual.

This is called Marketing.

 

[KenGordon]

@KenGordon the concern is how with the exact same settings the computer goes from something like 80/60 to 50/100. It is not a predictable algorithm. If you believe in it, fine, but in their own dive planner, it is doing some very strange stuff that makes no sense

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.