I want to murder my computer and feed it to the fishies!

[pheel]

So this makes me wonder (and forgive me if it is mentioned I am only halfway through the link you provided). Will the computer make deep stops at different depths for each dive, or will they always be at the same depth. Like for example will deep stops always be at 70, 55, 40 etc if they are needed, or will they vary for each dive? Because if they are always going to be at the same depth then easier to watch for them instead of relying on alarm.

Also, should I miss a deep stop, would going back down, or even maintaining a stop a few feet above have any effect on deco time? Or would it not even make a difference by that point to my computer.

More things to ponder and search for...

 

[Mr Carcharodon]

Ratio deco or running profiles on decoplanner or v-planner will give you framework on which to plan your dives and answer your questions. UTD and GUE have classes on RD (UTD may even have an online class) that would answer your questions on what to do if you stay down a little longer or go a little deeper than planned, and where to do your stops. But generally you will not get a full explanation here simply because it takes more than a paragraph or two to do and if you skip things you can get hurt. I suspect a RGBM computer will add deco if you go back down significantly since that would be a reverse profile. Uncle Pug had a good post on RD or planning on the fly. Keep asking questions, and be safe. Of course there is more than deco to planning your dives, so please do keep that in mind.

 

[kotik]

Melanie,

The people on this forum who might be qualified to answer your question are not going to answer what you are asking, because it's not the right question. Some of those people have tried to give you the answer to the right question you haven't asked though, and you've been determined to ignore them.

Your problem isn't that you don't understand what your Mares model XJ Zipadoo, s/n 1234, is thinking when it gives you 27 min of deco, when it gave you 20 minutes just a couple of minutes ago. That isn't something you're ever going to know until you get to go through the firmware source code and plug in the parameters and the data points from the memory log. Hopefully by the time you got to that point you'd realize that it's pretty irrelevant.

What your real problem is, is that you don't understand the kind of diving you're doing. That's obvious to those that know the subject matter, and they're not likely to help you along the path to crippling or killing yourself since you seem basically nice so far.

It's up to you on who you listen to, but the only one who can really give you a direct and authoritative answer to your question would be a software engineer from Mares, and I doubt that's in the works. There are some other good responses here that you might do well to think twice about. If you're truly interested in learning something worth the time, forget the computer-- get trained on safe planning and execution of technical dives.

Sorry if I seem a little harsh or in your face. There are surely people that have a little better diplomacy than I do that might be better help. If that ideal someone does happen to chime in, despite previous evidence that they'd be wasting their breath, I'm hoping you might entertain the possibility that you have something to learn from them... even if it's not exactly what you want to hear.

Best regards and safe diving to you,
Eric

 

[Doubler]

We always did deco by using navy dive tables, slate, depth gauge, watch and bottom timer. Personally don't trust electronics doing deco as I have had one fail on my first dive using it. Now like Dr. Bill I dive with two using the same program. You shouldn't miss stops if you have a plan written down and are paying attention. Put the Mares to gauge and PLAN the dive, using tables is good for you. Back in the day we didn't have all these different certs and most of us old farts who did deco were self taught. We did not have the lazy man tool of a dive computer or even a V
planner to just put our life in it's circuits. My advise is trust no computer, don't care what it cost, plan the dive using U.S. Navy dive tables then dive the plan. A dive plan also includes equipment to be used to safely complete the dive.

 

[melanie.]

We always did deco by using navy dive tables, slate, depth gauge, watch and bottom timer....My advise is trust no computer, don't care what it cost, plan the dive using U.S. Navy dive tables then dive the plan.

So what happens if your computer and the tables don't mesh? Which do you listen to? Speaking in NDL limits anyways, my computer is more conservative then the PADI tables. If I listen to tables alone - my comp goes into deco. If I don't listen to it then it locks me out for second dive. What's the point of having a computer if I don't listen to it as well? But the tables only plan for square profiles... (See the predicament?) How do you find a good middle balance?

Where can I find a copy of tables for deco dives? My searches (sleep filled mind) only produce rec tables. V planner has been interesting to play around with, but again I am worried that what I plan for with that might not be what my computer wants.

Back in the day we didn't have all these different certs and most of us old farts who did deco were self taught

 

[Slamfire]

RGBM has three factors that change the population of bubbles if you do bounce dives, reverse profiles, or repetitive dives (see “Decompression Theory” by B.R. Wienke). RGBM keeps the volume of gas in bubbles below a threshold value by controlling pressure gradient (difference between dissolved gas pressure and ambient pressure) and time.

I'll give this a try. Melanie, I will try to answer your questions directly and in a non-judgmental way.

Deco Stops
Mr. Carcharias is right. I have a Mares Puck that uses RGBM. I have seen it demanding inordinate amounts of time after a repetitive dive. I did plan that dive and was fully aware that the time it was requiring was not reasonable. After the dive, I went back to my manual and found out that under certain conditions, it will lower gradient factors which in turn will extend your required stops. The manual doesn't say much more than that. In other words, it does not tell you by how much or how this will affect a dive.

The end result is that you end up with the questions you are posing. How in the world am I supposed to plan for a dive when I have no clear indication exactly by how much the computer will extend my stops. It all boils down to the fact that this computer was not meant to plan and execute decompression dives. Simply stated, you don't have all the required information to do that. My Mares Puck has a "planning" feature but that feature only tells you what your NDL will be. It will never tell you what a deco obligation will be for a hypothetical dive. In other words, again, the algorithm as it is implemented in Mares Puck is not for planning or executing deco dives. The manual plainly says it and there are no features to plan and if you try to plan, as you did, to start ascent when you have x mins of obligation, the results are not predictable because the thing is changing gradient factors (ie. changing conservatism) on you. I suspect it is constantly changing gradient factors on the fly, but there is no information of exactly by how much, which makes this algorithm implementation unpredictable for deco obligations and you don't want unpredictability in your diving. Changing gradient factors on the fly would explain why time seems to go slower for the wretched gizmo.

Deep Stops
My Puck also has deep stops. The screen will NOT tell me about a deep stop until I reach the deep stop depth. I think this is crappy, or at least confusing design. I'm not sure if there is an audible alarm for it, but still, audible alarms with all the noise of open circuit scuba are so unreliable. Maybe the computer considers the deep stop to be more or less "optional". Before I get to the deep stop depth the screen will tell me that I have a deco obligation either at 20' or 10'. But as I get to ~43' the deep stop text lights up and a 1 minute countdown starts. If my bottom depth was 150' or deeper I can expect another deep stop at ~70'. I am not very familiar with planning deco dives on the RGBM algorithm to judge whether this deep stop strategy is logical or not.

The Good News
Does this make your computer useless for deco dives. Absolutely not. You can still use it in bottom timer mode for the execution part of the deco dive. You just cannot use it to plan a dive -- even if that planning is as simple as saying "I'll start ascending when I get 20 mins of deco obligation". You can even use it in regular mode and let it throw a tantrum when you surface and it still wants you to stay an additional 40 minutes under water. I do it like that all the time. One thing I do love about my Mares is that it will not lock me out completely if I disregard it's wishes -- it will only lock me out to bottom timer mode, which is all I really needed from it in the 1st place.

If you are still persistent in doing deco dives, you'll have to find another way to do the planning part of it. You CANNOT safely do a deco dive if you don't plan it first. The good news is that you really do not need to buy a $1000 dollar computer to plan and execute a deco dive. There are many desktop computer software packages that you can use to plan your dive adequately. Some of those are even free: MV-Plan the Java Dive Planner

Let's use a dive similar to the one you talk about in this thread as an example:

Settings: GF=30-80
=========================
DESC:130ft for 02:09 [ 2] on Air
DIVE:130ft for 27:49 [ 30] on Air
ASC : 60ft for 02:20 [ 32] on Air
DECO: 60ft for 01:40 [ 34] on Air
DECO: 50ft for 02:00 [ 36] on Air
DECO: 40ft for 04:00 [ 40] on Air
DECO: 30ft for 06:00 [ 46] on Air
DECO: 20ft for 09:00 [ 55] on Air
DECO: 10ft for 22:00 [ 77] on Air

Gas estimate based on Dive RMV =0.7, deco RMV =0.6cuft/min
Air : 151.0cuft
Oxygen Toxicity - OTUs: 31 CNS: 13%

Discipline
You write down the above plan in something you can take with you under water and only use your Mares to get to tell you what is your depth and dive time, nothing more. From the example above you know that you will do a 2 minute deep stop at 50 feet and you will be leaving 50 ft at exactly 34 mins into your total dive time. As you can see, you have to be VERY disciplined to do this type of deco diving. There is no computer adjusting the plan on the fly in case you failed to make it to the stop on time. And, honestly, you shouldn't depend on a computer to do that for you.

Gas Requirements
You can also see from the example above that the overall total time of the dive will be 77 mins and you will use up 151 cu ft of gas. A BIG HP 130 steel tank will only hold 130 cu ft. This means that for this dive you will need more than one tank -- so you see that wearing doubles is not just because they look cool. Could you get away with just wearing twin Al 80's? Well, an Al 80 doesn't really hold 80 cu ft. In reality it holds 77.4 cu ft. Therefore twin Al 80's will hold 154.8 cu ft. You will not have enough gas for you and your buddy if he experiences a regulator malfunction at depth. Also, what would happen if you get momentarily swept by the current and you have to swim hard for 3 mins to get back on track. The hard swim duplicated your gas consumption and now you don't have enough gas to complete the dive. Which brings us to the next topic:

Gas Consumption -- Measuring RMV aka SAC aka SCR
The above example assumes you have a gas consumption rate of 0.7 cu ft per min per atmosphere. How do I know if that is representative for me? Well, I have to measure my own consumption rates because they will most certainly vary from person to person. Not only do you have to have a clear idea of how much gas you consume during regular diving, but it is also very important to know how much gas you use up during psychologically and/or physically stressful situations. It will also be a good idea to know the consumption rates of your buddy, because you are a source of emergency gas for him.

In Conclusion
You cannot reliably use your Mares to plan deco dives. There are other non-expensive ways to adequately plan deco dives. You can keep on using your Mares in a bottom timer capacity to execute dives. The examples I give above are grossly oversimplified and for illustrative purposes only. They are not meant to replace proper (formal or otherwise) instruction on decompression diving.

I hope this helps.

 

[melanie.]

Slamfire - you are my new best friend. Thank you for your post, very clear, well written, and informative.

All the do's and dont's aside, you have answered as best as I think anyone could what I am experiencing with my computer. I never realized it could switch how conservative it wanted to be on-the-fly, and I guess me trying to predict what would happen was driving me nuts when there was no way I could do it. And frankly it caused me some stress watching it not count down as it was supposed to. Now I don't have to murder my computer, I will let it be its eccentric little self and plan accordingly (ie not with the damn thing).

Yes I know I still have more to learn.. never denied that. I just wanted a little peace about how crazy this was driving me. Now that I think I can handle this explanation... I can focus on the other stuff rolling around in my head.

 

[DuboisP]

Safety stop countdowns to me indicate a computer is not really intended for technical diving. If you want to do more deco alter the VPM conservatism settings or the Buhlmann gradient factors to an appropriate value rather than following some arbitrary 3 minute stop.

we have a difference of definition of "technical" diving
for you, it's a dive with deco, or a dive beyond 30 or 40m
for me, it's a dive with gaz switching on nitrox or oxygen or using trimix.

i'm using a Vytec DS which manages 3 binary mix, so it's a computer for "technical" diving, but you cannot change VPM or Bulhmann GF.
According you, it's a computer for recreational diving, so, why managing 3 mixes ?

 

[DuboisP]

Dr. Wienke, to my knowledge, has not publicly disclosed how the calculated number of seed bubbles changes with bounces, reverse profiles or repetitive dives. Nor have those factors, again to my knowledge, been validated.

you have to pay to get the literature.
it's not in the public domain.
some documentation is available on Suunto web site

 

[DuboisP]

If you are still persistent in doing deco dives, you'll have to find another way to do the planning part of it. You CANNOT safely do a deco dive if you don't plan it first. The good news is that you really do not need to buy a $1000 dollar computer to plan and execute a deco dive. There are many desktop computer software packages that you can use to plan your dive adequately. Some of those are even free: MV-Plan the Java Dive Planner

Let's use a dive similar to the one you talk about in this thread as an example:

Settings: GF=30-80
=========================
DESC:130ft for 02:09 [ 2] on Air
DIVE:130ft for 27:49 [ 30] on Air
ASC : 60ft for 02:20 [ 32] on Air
DECO: 60ft for 01:40 [ 34] on Air
DECO: 50ft for 02:00 [ 36] on Air
DECO: 40ft for 04:00 [ 40] on Air
DECO: 30ft for 06:00 [ 46] on Air
DECO: 20ft for 09:00 [ 55] on Air
DECO: 10ft for 22:00 [ 77] on Air

Gas estimate based on Dive RMV =0.7, deco RMV =0.6cuft/min
Air : 151.0cuft
Oxygen Toxicity - OTUs: 31 CNS: 13%

MVPlan is a good idea.
But it needs to understand what are Gradient Factors
In your example, you let GF 30-80, and these GF are for trimix diving.
for a dive with air, i prefer 90-90, so the stops will be less strange for rec divers

sorry, my mvplan is french speaking.

Configuration : GF=90-90 Factors:1.0/1.0 multi-niveaux PpH2O=2.041 ftem ZHL16B
=========================================================
DESC:130ft for 01:18 [ 1] on Air, SP: 0,0, END:130ft
DIVE:130ft for 28:41 [ 30] on Air, SP: 0,0, END:130ft
ASC : 30ft for 03:20 [ 33] on Air, SP: 0,0, END: 30ft
DECO: 30ft for 02:39 [ 36] on Air, SP: 0,0, END: 30ft M-Value: 90% [03], GF: 90%
DECO: 20ft for 08:00 [ 44] on Air, SP: 0,0, END: 20ft M-Value: 95% [04], GF: 90%
DECO: 10ft for 18:00 [ 62] on Air, SP: 0,0, END: 10ft M-Value: 95% [04], GF: 90%

Consommation de gaz basée sur VRM Plongée =0.88, VRM Déco =0.71cuft/min
Air : 167.6cuft
Toxicité oxygène - OTUs : 31 SNC : 12%