Algorithms, Conservative Factors, Altitude, Planned Deco - Questions

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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.
Hi Stuartv, thank you for responding to my additional questions regarding your diving and how you use your computers. The questions you have to Scubapro/Uwatec are valid and these are the same questions I have pondered over.

Let me take this opportunity to share my experience with heart rate training. First, to take advantage of this technology it is imperative that you work out your maximum heart rate (MHR). The formula of 220 minus age is too general. And your running MHR is not applicable to diving because water is supporting your body while diving. The MHR for diving or swimming is lower for the same amount of effort; about 10 to 15 beats per minute. The MHR has to be accurately determined because the trigger to change the decompression profile is going to be based on a percentage of MHR (or your heart rate reserve (HRR) which is the difference between your MHR and your resting heart rate). I suspect the trigger is around 85-90%. I wouldn't be surprised if many divers using the Galileos and G2 have left the heart rate settings at the default of 100/180 and the trigger never kicks in because the 180 is too high for a swimming/diving MHR.

When I go for my run, and I push my effort (workload) to 90% of my MHR - guess what happens to my respiration. It naturally increases because my body is demanding more oxygen. On land, I don't need a transmitter screwed into my neck like Frankenstein to monitor my breathing rate; respiration can be derived from my heart rate. The training software I use can graph my heart rate and my breathing rate; all from my heart rate monitor.

When you plan your dive, you are making assumptions about your average respiration. As long as you are calm and breathing normally, you complete your dive as planned. But say something happens at depth to increase your workload to 85-90% of MHR. You have 3 problems. First, you have to fix whatever it is to reduce your workload. Second, you consumed more gas than planned (increase workload naturally increases respiration) Third, because you inhaled more oxygen; you absorbed more nitrogen at depth. You muscles demand more O2 which your heart delivers, but O2's buddy is N2 who came along for the ride and doesn't necessarily want to leave!

So what do you do? Your plan is blown; it no longer applies. You have less gas than planned and you have more nitrogen in your system than planned. You go through your decompression profile and at 6 meters, hopefully the boat skipper has dropped two hookah lines for you and your buddy which is connected to a tank containing 100% O2 on the boat. And you suck that gas like an infant on his mother's breast until you get the all clear to surface; either by sucking the tank dry or by your dive computer which took into account the diving incident.

The idea behind the heart rate monitor is to objectively identify and measure an increase in workload so that it can be taken into account for your decompression. Your Shearwood kind of does the same thing but it measurement is subjective. On page 59 of the Perdix manual;

"The conservatism settings (GF High and GF Low) can be edited in the Dive Setup menu. While diving, only the GH High value can be edited. This allows changing the surfacing conservatism during a dive. For example, if you worked much harder on the bottom segment than expected, you may wish to add conservatism by reducing the GF High setting."

In my OP I asked Shearwood users what's in store for the future; what will they create so to make their Terics obsolete. Shearwood may incorporate heart rate monitoring but use a different approach to Scupapro/Uwatec. The additional deco obligation may be calculated in the background and a warning message pops up saying; Workload Increase. Suggest change GFhi 85 to 75. Then it leaves it up to the diver to decide if he wants to make the switch or not. This approach may be more acceptable to divers because it leaves them in control of their decompression profile.
 
The bubbles are obviously a marketing gimmick. Each setting will be changing the limiting m value a bit, sound familiar?
I have to agree, Over a decade ago or more if you wanted to be a "real diver" then you wore an Uwatec Alladin X or Z or some letter at the end of the alphabet. Then Suunto and Wienke came out with the bubble model and everyone raved about it. And the guys at Uwatec thought; "Oh sh*t, we've only got this old fart 8 tissue Bullshi...mann model while this Wanker or Wienker or what ever his name is, is blowing bloody bubbles out his arse and stealing market share. We gotta do something! Hey lets call our conservative factors Microbubble levels! Now we are back in the game!"
 
The computer manufactures followed the fashion by adding deep stops, either Pyle style (like the Helo2 and maybe this ScubaPro), by GF (30/70 anyone?), VPM or otherwise (Eon etc).
And the guys at Uwatec again thought; "Oh ****, some idiot is talking a Pyle of crap, of staying deep for two minutes to reduce these bloody bubbles. Those Japanese at Suuntory are now marketing Deep Stop and stealing market share. We gotta do something! Hey, lets take a simple concept and complicate it. We'll call it PDIS for "Pyle, Dumb Idea Sorry!"
Now we're back in the Game!
 
As part of my investigation, I reviewed the Scubalab results for 2016 and 2017 to determine how conservative each computer really is. Scubalab conducted 4 multilevel dives and recorded the NDL at each depth for each computer. I simply summed these figures on the basis that comparatively lower total NDLs are more conservative. This gave me the ability to rank the computers on each dive as well as provide an overall view. As you can see from my attached table, Scubapro was one of the most conservative computers overall and generally across all dives. The dives profiles were the same each year and Perdix was included both years with different results. This difference may have been due to different GF's selected. See attached PDF.

FYI - I did the ranking a bit differently, but would probably even do it differently again by weighting it or ignoring the less stable and or less relevant NDL depths - Place of dive tables in modern diving

The last couple of pages on this thread are interesting re how to properly assess the conservatism of a dive computer [Edit for Rec / NDL diving]: First Dive Computer
 
And the guys at Uwatec again thought; "Oh ****, some idiot is talking a Pyle of crap, of staying deep for two minutes to reduce these bloody bubbles. Those Japanese at Suuntory are now marketing Deep Stop and stealing market share. We gotta do something! Hey, lets take a simple concept and complicate it. We'll call it PDIS for "Pyle, Dumb Idea Sorry!"
Now we're back in the Game!
Lol.

Everyone should take a bottle, drink one shot it at half max depth minus a bit and repeat, at each half depth following. When they get to 6m they should finish the bottle, then surface. You choose the bottle size by the depth. So called no stop dives use miniatures, 30m plus a half bottle and 60m plus a full bottle.

As a bonus the nitrogen narcosis continues as you get shallower so it is as if it never happened.

Those who believe in bubbles can use champagne instead but should be cautioned that they might need to wait longer than expected at the last stop, so not to swig it down too fast. Research is underway, but not expected to have meaningful results until after Christmas.
 
Let me take this opportunity to share my experience with heart rate training. First, to take advantage of this technology it is imperative that you work out your maximum heart rate (MHR). The formula of 220 minus age is too general. And your running MHR is not applicable to diving because water is supporting your body while diving. The MHR for diving or swimming is lower for the same amount of effort; about 10 to 15 beats per minute. The MHR has to be accurately determined because the trigger to change the decompression profile is going to be based on a percentage of MHR (or your heart rate reserve (HRR) which is the difference between your MHR and your resting heart rate). I suspect the trigger is around 85-90%. I wouldn't be surprised if many divers using the Galileos and G2 have left the heart rate settings at the default of 100/180 and the trigger never kicks in because the 180 is too high for a swimming/diving MHR.

Have a read of Are You Dive Fit? - Divernet
 
Third, because you inhaled more oxygen; you absorbed more nitrogen at depth. You muscles demand more O2 which your heart delivers, but O2's buddy is N2 who came along for the ride and doesn't necessarily want to leave!

So what do you do? Your plan is blown; it no longer applies. You have less gas than planned and you have more nitrogen in your system than planned.

This is incorrect. At least, according to all the decompression theory with which I am familiar.

Your nitrogen loading is based on the difference in partial pressure of the gas you're breathing versus the gas in your tissues. Your breathing rate has no effect on how much nitrogen is absorbed.
 
As part of my investigation, I reviewed the Scubalab results for 2016 and 2017 to determine how conservative each computer really is...

https://www.scubaboard.com/communit...-in-modern-diving.557445/page-32#post-8235124

I did the ranking in yet a third way, the results are the same. Buhlmann 45/95 and DSAT are liberal. Buhlmann 40/85, PZ+, and Suunto RGBM are middle of the road/moderate. Mares RGBM, Cressi RGBM, and Scubapro Buhlmann ADT are conservative. Taking a quick look at the results gives the same impression as a calculation.

The 2018 computer review is in the November issue. I emailed Roger Roy and he tells me the hyperbaric testing results will be posted soon
 
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This is incorrect. At least, according to all the decompression theory with which I am familiar.

Your nitrogen loading is based on the difference in partial pressure of the gas you're breathing versus the gas in your tissues. Your breathing rate has no effect on how much nitrogen is absorbed.
@CandiveOz, @stuartv is correct here, I believe you have a misconception on this topic
 
To expand a bit: Breathing rate does not affect nitrogen loading.

It's easy to mix breathing rate and workload together and have the impression that breathing is a factor. That is because working hard DOES increase the chance of a DCS hit. Working hard would generally correlate with increased breathing. So, it's easy to understand how one might think that increased breathing means increased inert gas loading.

However, (and note that I am NO expert here - I am now venturing off into my own layman's pet theory) the increased chance of a DCS hit after working hard is not because of an increased load of inert gas. It is because the work makes the existing load of inert gas more likely to bubble.

I think it is very much like a soda bottle. The same amount of gas is in the bottle, no matter what you do. But, if you shake it before you open it, it's a LOT more likely to fizz.
 

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