Algorithms, Conservative Factors, Altitude, Planned Deco - Questions

[dmaziuk]

Actually lots of Gekko, Zoop, Vyper, Viper Air (which does multiple mixes) and of course Helo2.

So the interesting question then is how the "fused" RGBM stacks up to "folded" RGBM, especially when you go on "light deco".

The dive I mentioned earlier, the DM was wearing an EON Steel and when the couple with maxed-out on safety Gekkos got out of the water, there was a bit of a discussion of the algorithms and conservatism factors. DM's EON had another quarter hour or something NDL at max depth that we just came up from. I think he was on default conservatism setting.

To me as a vacation diver, another interesting question is how "folded" RGBM reacts to repeated deco: there is "no penalty" for overstaying your no-stop time and completing your deco to computer's satisfaction, but there is extra conservatism for repeated dives and bubble excitation magic. I would assume that last bit to get greater if one consistently hits the M-value line and has to make mandatory stops there, and so in practice there well may be NDL reduction for subsequent dives.

Not that that's necessarily a bad thing...

 

[Diving Dubai]

So the interesting question then is how the "fused" RGBM stacks up to "folded" RGBM, especially when you go on "light deco".

I can only answer with the little knowledge I have. According to Suunto (I believe there is a graphic on teh Suunto site somewhere) Fused RGBM switches over from vanilla RGBM to Tech RGBM at 30m, so when shallower teh Eon should behave is a similar manner to other Suunto products.

From anecdotal experience of guiding, if I set my Eon to default (P-0) then it shows little difference in NDL between itself and other RGBM computers above 30m. I can't say for certain how would change on repetitive light deco dives alongside other RGBM computers, because I rarely get a chance to compare. I also know from experience that despite the NDL difference mid dive, my Eon and Perdix both hit deco at the same time and give the same amount of time (as opposed to what Andy wrote in his BS blog)

If I'm teaching Con ed, I may have 2 different classes on the same day(s). For Instance I had AOW and Wreck the other weekend. For me that meant 5 dives per day over the weekend. My solution was to wear a different shop computer for each group, and run my computers at their most aggressive. In that way I could balance my small deco obligations while giving them the max time within their NDL

 

[CandiveOz]

US agencies all traditionally regarded deco diving as the work of the devil,

I had a good laugh when I read this. If deco was the work of the devil, then PADI was the Vatican. I remember learning PADI tables when I started diving but switched to the Canadian DCIEM tables because unlike PADI, these tables offered decompression profiles if you exceeded the NDL times. And even if I conducted a no decompression dive, I would practice these deco profiles while clipped to the anchor line. I actually found it quite relaxing and would fine tune my buoyancy control. Sure, I was the last diver in the boat but my buddies didn't care since they were having a cup of tea and munching on my share of Tim-Tam biscuits.

As for Suunto computers, my questions have been answered. Suunto in Australia is very popular but the EONs, like the Shearwaters, are currently non-existent in the secondary market. The other models are available so I still have a choice.

Oceanics are also popular, but I am a little bit disappointed in the black box. These computers have all the bells and whistles including dual algorithms, multi gas switching etc but really offer no ability to plan a deco dive; unless I missed something. Anyone please chime in if my conclusion is mistaken.The Oceanic website it does state that the decompression capability of its computer is 3-18 metres but that's meaningless to me.

Its probably due to my personal experience with my old DCIEM tables. I may not necessarily do a deco dive, but I want to know what my obligation is if I do and preferably before the dive. I like to test the algorithm in a number of scenarios and understand its limitations to get a feel for it; similar to what I did in Suunto's DM5 to better understand its conservative/altitude factors.

As for Scubapro, I have yet to receive any feedback. Hopefully members with Scubapros will read this post, share their experience and address my queries.

 

[KenGordon]

If you want Trimix, consider a Helo2, otherwise a Vyper Air. They can be quite cheap secondhand and will do what you need.

 

[scubadada]

Hi @CandiveOz

Best of luck in your computer purchase, you seem to be taking your research seriously.

As mentioned, I believe most divers seriously considering technical diving would choose a computer running Buhlmann ZH-L16B/C. There are an increasing number of brands available, including Divecomputer.eu/Deep 6, Dive Soft, Garmin, Heinrichs Weikamp, Ratio/Seac, and Shearwater. Only the latter 3 offer AI. For Ratio, the Easy and Deep models offer presets only, you must go with a Tech+ to get custom GFs.

Suunto actually has 3 flavors of RGBM, plain RGBM, Technical RGBM, and Fused RGBM. Technical is run on the HelO2 and the D9tx. Fused is run on the DX, Eon Steel, and Eon Core. All other models run plain RGBM. Fused RGBM runs Technical until it transitions to full RGBM at depth. For gases without helium, transition starts at about 130 feet and is complete at about 180 feet. So, for recreational depths on air or nitrox, Fused RGBM and Technical RGBM computers are the same. These computers offer a fair amount of adjustment between P-2 and P2. For an air dive to 30 meters the NDL ranges from 14-20 min. P-2 is 20 minutes, same as DSAT. P1 is 16 minutes, same as PZ+. You may be penalized for short SIs, reverse profiles, sawtooth profiles, multiday diving, and/or ascent rate violations, consistent with the bubble model.

I have been diving Oceanic computers running DSAT since 2002, about 1600 dives. You are correct, you are not able to plan deco dives with these computers and they are not designed for technical diving. Nearly all of my diving is no-stop with about 5% being light deco. My Oceanic computers are adequate for these short, shallow stops. I have several hundred dives using a Dive Rite Nitek Q running Buhlmann ZH-L16C with GFs as a backup. This has given me a fairly good understanding of how Buhlmann runs compared to DSAT. Should my Oceanic computers die, it would be easy for me to switch to a computer running Buhlmann. I own several PPS transmitters that would allow me to more inexpensively switch to a Perdix AI or Teric.

Good diving, Craig

 

[dmaziuk]

I can only answer with the little knowledge I have. According to Suunto (I believe there is a graphic on teh Suunto site somewhere) Fused RGBM switches over from vanilla RGBM to Tech RGBM at 30m, so when shallower teh Eon should behave is a similar manner to other Suunto products.

The "folded" version is designed for low-power devices unable to run the full iterative thing. It boils down to folding RGBM magic into a simplified formula for adjusting M-values, AFAIK there's a pdf somewhere with a fairly general hand-wavey description. Basically like fine-tuning a/b coefficients plus gradient factors to closely mimic the "RGBM proper".

Usual questions with this approach is "how closely" and "over what range of inputs": if they worked exactly like the real thing all the way, only at much less compute load, then who'd ever need to run the real thing?

Point being that Suunto has a pdf showing how EONs behave, but it's not clear that Zoops will behave exactly the same way for, say, longer deco times.

 

[Diving Dubai]

Fused RGBM runs Technical until it transitions to full RGBM at depth.

Hi Craig,

I'm sure in yoru head you meant it the other way around...

With Fused, it switches from Standard RGMB to Tech RGBM at 30m, so at depths shallow than 30m (ish) you're on Standard RGBM so it behaves the same way as normal RGBM computers although the conservitism settings don't match exactly (but P0 is near enough).

I'm going to get a battery for my Leonardo and have that on my wrist next time to see the differences between the Eon and Perdix

 

[scubadada]

Hi Craig,

I'm sure in yoru head you meant it the other way around...

With Fused, it switches from Standard RGMB to Tech RGBM at 30m, so at depths shallow than 30m (ish) you're on Standard RGBM so it behaves the same way as normal RGBM computers although the conservitism settings don't match exactly (but P0 is near enough).

I'm going to get a battery for my Leonardo and have that on my wrist next time to see the differences between the Eon and Perdix

Hi Martin,

No, actually, the Suunto computers running Fused RGBM, run Technical RGBM until they transition to full RGBM. With air and nitrox, the transition starts at 40 meters. With >20% helium, the transition starts at 30 meters. There is a link to a longer PDF describing Fused RGBM in this brief description of the 3 Suunto RGBM deco algorithms Suunto RGBM Dive Algorithms So, at recreational depths, diving air or nitrox, the Core, Steel, and DX run like the HelO2 and D9tx

 

[Diving Dubai]

Hi Martin,

No, actually, the Suunto computers running Fused RGBM, run Technical RGBM until they transition to full RGBM. With air and nitrox, the transition starts at 40 meters. With >20% helium, the transition starts at 30 meters. There is a link to a longer PDF describing Fused RGBM in this brief description of the 3 Suunto RGBM deco algorithms Suunto RGBM Dive Algorithms So, at recreational depths, diving air or nitrox, the Core, Steel, and DX run like the HelO2 and D9tx

You're right by golly!!

That's not how it was explained to me by Suunto,... Running DM5 though it all stacks up.

That said in real world against Normal computers (Zoop, D4 D6 etc) less than 30m dives there is little difference, I'll see what I can make happen on my next trip out

 

[scubadada]

You're right by golly!!

That's not how it was explained to me by Suunto,... Running DM5 though it all stacks up.

That said in real world against Normal computers (Zoop, D4 D6 etc) less than 30m dives there is little difference, I'll see what I can make happen on my next trip out

I've learned a lot from you, look forward to hearing more about comparisons between Suunto Fused, Buhlmann, and now, Cressi.

Diving DSAT and Buhlmann together has taught me quite a bit