Algorithms, Conservative Factors, Altitude, Planned Deco - Questions

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

Thanks for the recommendation Ken, the suunto Dx's which run the new Fused algorithm have hit the secondary market here so that is another alternative to consider (although the asking price is a little higher). BTW I had a little chuckle regarding your comments in another post about divers selling their Perdix to buy two Terics! Please don't discourage these guys, I depend on these types to buy the latest and greatest! :wink:

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.

Scubadada, I read the article you cited. Doesn't this mean that there are actually 4 flavours of RGBM, Plain vanilla, Tech and Fused, which is a combo of Tech and "Full." My understanding is Full is for deep diving only (not applicable for shallow depth) and therefore different to plain vanilla RGBM which is more applicable to recreational activities such as multidives, short surface intervals etc. I guess the Full isn't a complete "flavour" because it doesn't cover the complete spectrum of depth but it is unique to the original RGBM firstly developed. Let me know if I have misunderstood the article.

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

Would you please explain what "folded" RGBM is? Is this another flavour?
 
...Scubadada, I read the article you cited. Doesn't this mean that there are actually 4 flavours of RGBM, Plain vanilla, Tech and Fused, which is a combo of Tech and "Full." My understanding is Full is for deep diving only (not applicable for shallow depth) and therefore different to plain vanilla RGBM which is more applicable to recreational activities such as multidives, short surface intervals etc. I guess the Full isn't a complete "flavour" because it doesn't cover the complete spectrum of depth but it is unique to the original RGBM firstly developed. Let me know if I have misunderstood the article...

You appear to be generally correct. There appears to be 3 versions of RGBM used by Suunto, plain, tech, and full. It just so happens that the computers running Fused RGBM run 2 of the versions, tech at shallower depths and full at deeper depths. All their other computers run a single version, plain or tech.
 
Thanks for the confirmation because like Diving Dubai, I thought Fused was a combo of Plain and Tech until you pointed out the article.

Thanks again.
 
Would you please explain what "folded" RGBM is? Is this another flavour?

Nutshell version is in #26, scroll down to p. 18 in http://www.divetable.de/skripte/rgbm.pdf for the "horse's mouth" version.

As I said in #26, an approximation by a simplified formula tends to work well enough over a limited range of input values. This "folded" approximation is used in "recreational" computers, it's probably reasonable to assume that it works well enough on no-stop dives to above 60 metres. What does it do if you go deeper and/or longer?

I think the other question is tunable fudge factors. E.g. would you consider ZHL16-B. ZHL16-C, -B w/ GF 45/70, and -C w/ GF 50/85 "four different flavours" of Buhlmann? Or the same Buhlmann with 4 different "conservatism" settings?
 
Stuartv, thanks for your comprehensive response. Just for my own clarification, when you say you use your Oceanic as back up, do you only use it in gauge mode with a printed bailout table? Or is it so liberal compared to your GF setting on the Shearwater that you let it run in dive mode and if the Teric fails you just follow the Oceanic deco profile?

You also mentioned that the Oceanic was more liberal than the Seabear. Is that because the Oceanic was using the DSAT algorithm versus the PZ+?

[snip]

I completely understand your tech argument for planning your dive and diving your plan. Good advice. And you are correct, the biometrics of the Scubapro can be turned off if required. But as a previously bent diver I appreciate that these inwater adjustments are trying to make the dive safer and perhaps should be taken into consideration. If it is an issue of gas capacity; then carry more gas. When I started diving, I sucked air like it was going out of style. So back in 2001 I bought a 15 ltr Faber (I think that's 125 cu ft in North America). Since then my SAC has improved but I am still humping that tank on all my dives. My buddies either use 10 or 12 litres so by the end of a typical dive, I've got enough air for the both of us. Also, if I set my computer to be conservative, I can still match my buddy's default air NDL's by diving nitrox which pushes out my conservative NDL's. So with a bit of ingenuity, one can dive conservatively, have enough gas and match your buddies NDL's to surface together.

When I have used my Oceanic as a backup, I have carried a written plan that I could follow if needed. I have only used it as a backup on technical dives where the planned deco was pretty light. What I have observed is that, in those case, leaving it dive mode (instead of gauge mode) has never resulted in a violation. However, with a bigger dive involving multiple deco gases and longer deco times, I expect that doing that WOULD result in a violation. The thing that some people seem to not get about having a violation is that it doesn't lock you out. It just locks you INTO Gauge mode. So, even if that happened, with my written plan, I could still use it just fine (in gauge mode) to get out safely.

My Seabear (RIP) was a fully capable tech computer, just like my Shearwaters. I ran the Seabear with the same gradient factor settings as my Shearwater. Thus why the Oceanic was more liberal.

Regarding what you said that I bolded: The problem is how much more gas do you carry? When you plan a tech dive, you need to plan for all your contingencies and know how much gas you need for every contingency. If your computer is set to allow it to add deco time based on factors like your heart rate or skin temp, then I don't know how you could plan out ahead of time what the dive profile will be so that you KNOW you are carrying enough gas.

I suppose the ScubaPro planning software could have a "worst case" option for planning, where it would give you a profile based on the "most conservative" ascent that the computer would give you. But, that assumes that the computer's algorithm has known limits to what its worst case would be. So, does it? Does SP document anywhere what the worst-case limits would be? I.e. if it increases deco when your heart rate is at 150bpm, will it increase it further if your heart rate is 160? Is there a max heart rate where the deco would not increase if the heart rate increased any further? Is there a skin temp that would increase deco requirements? Is there a minimum whereby if you get even colder, the deco will not increase any further?

I don't know the answers to any of those questions. But, as long as they are unanswered, there is no way I'd do any technical dives with a computer that could be influenced by biometric factors.
 
Regarding what you said that I bolded: The problem is how much more gas do you carry? When you plan a tech dive, you need to plan for all your contingencies and know how much gas you need for every contingency. If your computer is set to allow it to add deco time based on factors like your heart rate or skin temp, then I don't know how you could plan out ahead of time what the dive profile will be so that you KNOW you are carrying enough gas.

I suppose the ScubaPro planning software could have a "worst case" option for planning, where it would give you a profile based on the "most conservative" ascent that the computer would give you. But, that assumes that the computer's algorithm has known limits to what its worst case would be. So, does it? Does SP document anywhere what the worst-case limits would be? I.e. if it increases deco when your heart rate is at 150bpm, will it increase it further if your heart rate is 160? Is there a max heart rate where the deco would not increase if the heart rate increased any further? Is there a skin temp that would increase deco requirements? Is there a minimum whereby if you get even colder, the deco will not increase any further?

I don't know the answers to any of those questions. But, as long as they are unanswered, there is no way I'd do any technical dives with a computer that could be influenced by biometric factors.

You are saying “if I cannot know how much extra gas might need due to these biometric factors I will rather ignore them completely”. But you do dives and discover you gas use rates, you don’t know those until you figure them out. You will figure out the impact of the biometric stuff on your plans the same way. Also you have double the deco gas your plan requires. So unless you need double the deco due to these factors (or your buddy has an issue) your are good. And IF those factors matter then you should be staying down longer.

I am guessing, based on how the general conservatism seems to work, that you will not bend the computer until you ignore the base (most aggressive) conservatism. I’d need to read the manual again, or try one out.

Ideally they’d start from a more aggressive position and back down to ‘normal’ based on what is measured and then on to more conservative. I bet the product liability people wouldn’t let them though.
 
Thanks for the recommendation Ken, the suunto Dx's which run the new Fused algorithm have hit the secondary market here so that is another alternative to consider (although the asking price is a little higher).

Personally I am not very keen on the DX or the D9tx. I am anti watch style computers in general and expensively ones in particular. They are both quite expensive. The bloke I know who had a D9tx has replaced it with an Eon. The bloke with a DX is often to be seen using an OSTC instead. Both do have decent battery life though. The DX has been out 6 years. There ought to be a replacement along soon... maybe the Teric will push a bunch of people,to get rid of DXs, but I don’t think they were very popular. I see people buying D4is at the drop of a hat though.

These days I always take the Perdix. That is because I can download logs easily. OC I take a Helo2 as backup. I used to use a Zoop and tables as backup and bend it. Mostly though, for CCR deco dives, I have a Petrel and the perdix. Previously I used the Helo2 as the backup on CCR dives. It doesn’t do constant ppO2 but it is close enough for a backup.
 
You are saying “if I cannot know how much extra gas might need due to these biometric factors I will rather ignore them completely”. But you do dives and discover you gas use rates, you don’t know those until you figure them out. You will figure out the impact of the biometric stuff on your plans the same way. Also you have double the deco gas your plan requires. So unless you need double the deco due to these factors (or your buddy has an issue) your are good. And IF those factors matter then you should be staying down longer.

I don't really see how that works.

I do some dives and work out what my gas consumption is. I then use that data to plan a tech dive and figure out how much gas I will need. I can do that such that my gas requirement is worst case and then be confident that I will have enough.

I don't see how that translates to "figuring out" the impact of biometric stuff. Is there a way for me to run the SP desktop software and tell it to generate a plan based on a heart rate of 150 and a skin temp of 86? If not, that how can I run a plan ahead of time and be confident that the deco it assigns me is the worst case deco requirement?

As far as carrying double the deco gas, that is because half of it is my buddy's. What you just said means that if my deco requirement is higher AND my buddy loses his deco gas, then one of us is screwed.

Bottom Line: You are the only person I have ever seen suggesting that technical diving (and I don't mean sport divers doing "light" deco) using a computer that will adjust your deco based on biometric factors is okay. To me, it is not okay. Period. I am done discussing it unless and until more credible support for this notion is presented.
 
If, however, you find your dive to be less cold and/or strenuous than planned, you will happily reduce your GF to deco on "less conservative" setting, didn't you say that elsethread? So that biometric stuff is perfectly OK as long as it makes your deco shorter?
 
If, however, you find your dive to be less cold and/or strenuous than planned, you will happily reduce your GF to deco on "less conservative" setting, didn't you say that elsethread? So that biometric stuff is perfectly OK as long as it makes your deco shorter?

I will bet you a dollar no dive computer manufacturer will ever put in any feature that automatically makes the computer more aggressive (i.e. gives a longer NDL or less deco).
 

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