Bottom Timer and Tables vs. Computer

[Pez7378]

I'm not sure if this should be here or in the Education forum

I imported this over from another board because I thought it might be helpful to anyone here who is interested in this sort of thing.

I want to thank Doug for his well thought out response, and for putting it into words I can understand.

I am thinking of switching to just a BT and MDL. I'll probably get a BT and run the tables parallel to my computer until I feel confident that I know what I'm doing. It's my understanding that this is more common in the DIR/UTD arena and that generally DIR divers state that this way of diving is Safer. How is it safer to follow the tables which are not as conservative as any computer? Did I miss something in class when we were talking about MDL?

I'll help you, buddy.

The general thought on a computer is that it is not needed, which is consistent with the DIR/UTD philosophy of "if it is not needed, don't take it."

Computers also tend to lead to people not generally planning their dives (let's go down and come up when the computer tells me to) which also leads to not thinking about such things as gas planning. Reduced overall awareness if you will. Included in this is the repetitive diving component, how many people do you see on a dive boat figuring residual nitrogen and stuff like that?

Also, computers may run different algorithms, and different computers on different teams may lead to different run times. This can lead to arguments among team members about what is proper deco and what stops to do where.

Is this so critical in the recreational context? Probably not. I ran my Suunto Vyper in computer mode for ~100 recreational dives and never bent it, meaning I really wasn't doing anything aggressive at all. But, I had generally gotten away from relying on it and was planning minimum deco dives from about dive 50 on. At one point I just switched it over to gauge mode because I got sick of telling it I was diving 32% all the time.

In the technical context there really isn't a computer that runs an algorithm that incorporates deep stops and the types of profiles advocated by most UTD types. This is one reason why dives are planned with tables/software such as deco planner or RGBM stuff (or, err, using other methods and black arts).

But, all that being said, the minimum deco tables are simple. 100/30 setpoint, five minutes less bottom time each ten feet deeper, five minutes more bottom time ten feet shallower. This is for 32%, and assumes you are doing at least minimum deco (1 minute stops at 50% of your depth up, or 2 minutes if repetitive dive within one hour of each other).

That is all I need to know for recreational diving, simple really.

Plus bottom timer=cheap. The loaded version (a Tech 2G) is ~$450, much less than a bells-and-whistles tech computer, and a simple one (Uwatec BT) is less than $200 or so.

I started looking at different tables, and I noticed differences in recommended Bottom time depending on the depth of the dive etc. for example one Minimum Deco table I looked at (Buhlmann I think) says 60 fsw for 85 min. on 32% with stops at 40/30/20/10 and the Naui (RGBM) tables say 60 fsw for 100 min. on 32% with 0 mandatory stops. But then at 100 fsw the Buhlmann model says to do 35 min. same stops, same mix and the Naui tables say to do 30 min with 0 stops. Apparently this is not an Exact Science? I think I'll stick with the computer for awhile

[Joshua Smith]

Personally, I like having a computer. I back it up with a bottom timer. If I'm doing a deco dive, I cut tables. I use vplanner for that- plus, I tweak them just a bit, and freely add time to them. I can't think of one time my computer was as conservative as the tables I cut, but: I've done dives where we hit max depth and aborted right away, for whatever reason. I didn't cut tables for 6 minutes at 180', or whatever. But my computer did. So I can safely get out of the water much faster.It's nice to have as a backup, plus it tracks no deco time......why not have one? I've heard it said that different computers will generate different deco schedules. I say: "So what?" Follow the most conservative one on your team, and if you really are deco diving, you're following tables anyway.


That applies to OC and CC for me. This part is CCR specific: I have a constant P02 computer that tracks the PP02 of my dive, factors in whatever mix I'm using for diluent, and generates deco profiles based on that. Same rules apply as above, BUT, it's a huge comfort to me to have yet another way of tracking my decompression.

At the end of the day, I simply don't see a downside to having a computer.

[LCF]

I think one of the things that really surprised me, when I started reading about decompression, was that different algorithms can give quite widely different no-deco times, on the order of ten or fifteen MINUTES difference at the same depth in some cases. That was when I began to realize that decompression is a very poorly understood subject, and that the mathematical models that are used are based on some simple test-tube physics and not on any physiological measurements. They are then validated by diving, and a certain amount of DCS is considered within acceptable thresholds.

Although I have heard rumors that there were some US Navy studies of actual gas tensions in tissues, I've never seen the references, and the studies are old. The closest thing to objective measurements being done now are the studies monitoring bubbling on Doppler, post-dive, and the big problem with that is that the amount of bubbles doesn't correlate very well at all with the level of symptoms.

Tables are a very crude way of implementing the algorithms, and computers are a continuously iterative procedure using the same calculations. But in both cases, there is little "accuracy", because the processes simply aren't that well understood.

I decided to go ahead and use the minimum deco method, because it's simple and easy for me to implement (especially compared to tables!) and it doesn't leave me dependent on the computer software or electronics. Keeping track of my own profile makes me stay very alert to where I am and for how long, which I think is a good thing, too. But I think you have to dive very often and work at this to get good at it, and the vast majority of people who dive infrequently, or take a few trips a year, are way better served to use a computer.

[Burntchef]

Apparently this is not an Exact Science? I think I'll stick with the computer for awhile

you are correct sir, give that man a prize!!! prize to be given away by nailer

iam sure brian will go over table cutting with you and joe, it was a bit hard for me at first but i just had to sit at home and cut a bunch to get the hang of it. i learned the peter/matt den haan method of padding tables for extra safety . i love knowing that at every stop iam ahead of the curve and by the time i surface i should of scarred off all the nitrogen gremlins with my deco mix. stupid freakin gremlins.

but yea i like having a comp to back up what i know in my mind. of course i dont currently have a he comp and use a b/t but my buddy does and what is his underwater is mine too

[dsteding]

I started looking at different tables, and I noticed differences in recommended Bottom time depending on the depth of the dive etc. for example one Minimum Deco table I looked at (Buhlmann I think) says 60 fsw for 85 min. on 32% with stops at 40/30/20/10 and the Naui (RGBM) tables say 60 fsw for 100 min. on 32% with 0 mandatory stops. But then at 100 fsw the Buhlmann model says to do 35 min. same stops, same mix and the Naui tables say to do 30 min with 0 stops. Apparently this is not an Exact Science? I think I'll stick with the computer for awhile

Okay, but do you do/know/understand what the computer is telling you? And, why is it better to stick with the computer rather than figure out which of the above tables works for you.

I know many divers that used to dive straight Buhlmann algorithm computers, go up to 20 feet and hang out and wait until it clears. A few of them that switched to, say deeper stops and different curve shapes, saw a noticeable improvement in how they felt post-dive.

The "I'll stick with a computer" mentality is understandable, and okay. But, I have to ask "what is that computer doing, what is the algorithm it is following, and do you understand it and trust it?"

[Joshua Smith]

I know many divers that used to dive straight Buhlmann algorithm computers, go up to 20 feet and hang out and wait until it clears. A few of them that switched to, say deeper stops and different curve shapes, saw a noticeable improvement in how they felt post-dive.

The "I'll stick with a computer" mentality is understandable, and okay. But, I have to ask "what is that computer doing, what is the algorithm it is following, and do you understand it and trust it?"

I don't understand deco theory any better than, well, most divers. I'm starting to find out what does work for me, though. And until I have it figured out to a gnat's ass, I'll wear a computer. (mine has adjustable gradient factors, and I like that. )

[dsteding]

I know many divers that used to dive straight Buhlmann algorithm computers, go up to 20 feet and hang out and wait until it clears. A few of them that switched to, say deeper stops and different curve shapes, saw a noticeable improvement in how they felt post-dive.

The "I'll stick with a computer" mentality is understandable, and okay. But, I have to ask "what is that computer doing, what is the algorithm it is following, and do you understand it and trust it?"

I don't understand deco theory any better than, well, most divers. I'm starting to find out what does work for me, though. And until I have it figured out to a gnat's ass, I'll wear a computer. (mine has adjustable gradient factors, and I like that. )

Josh, are you using VPM, like in a Shearwater? What GFs are you using? 30/85?

RIchard best referred to GFs (developed by GUE in Deco Planner, ironically) as "kludge" factors to force deeper stops. I've monkeyed with them a bit using VPM (Freeplanner and V-Planner) and can kinda generate profiles I like to dive.

My typical 150 feet for 20 minute profile would have stops starting at 110 feet for 1 minute and continuing up to my gas switch. Then, 3,3,1,1,3,6,4 to the surface (although 2,2,2,2,3,6,4 is something we've been debating moving to). This gets things a little deeper in terms of first stops and shape of a curve than pure VPM with GFs.

Can you post a screenshot of some of your profiles? Might be fun to compare notes.

I'm trying to do it with JTrak, but for some reason I cannot grab the screen or even print the profiles. Hmmmm . . . .

[Pez7378]

Apparently this is not an Exact Science? I think I'll stick with the computer for awhile

Okay, but do you do/know/understand what the computer is telling you?

Kinda, but I'm also kinda dumb.

And, why is it better to stick with the computer rather than figure out which of the above tables works for you.

Well, because I'm still trying to understand all of this mumbo jumbo. Seriously, I think if I keep asking the same questions over and over, I may still get the same answers but sooner or later someone will dumb it down enough that I suddenly "Get it".

[mattwave]

One thing to add to Doug's comments on trusting and knowing the computer's algorithm, what brings me back time and time again is how many Sat divers whether military or commercial are relying on their computers. Cochran estimates that thousands of their computers are used each and every day around the world for Saturation diving where their Algorithm is being trusted by divers who are spending days or even weeks at depth. AP Diving decided to use a Gradient Factor based Algorithm because the Royal British Navy has been using is for Decades with great success. Yes surface generated tables that are padded seemingly will always keep you in the water longer than either GF or EMC Algos onboard a computer will dictate. But hey we like being underwater and it's nice to know our Computers concur, we are safe to surface.
:rr:
I totally understand the comment that don't bring what you do not need, but I would think a computer on your wrist could be considered a back up just as a mask in your pocket?

[Pez7378]

And, why is it better to stick with the computer rather than figure out which of the above tables works for you.

After reading this again, another thought came to mind. Now it could just be my lack of understanding but in order to figure out Which tables work for me, I'd also have to learn which ones don't work for me, which means experiencing DCS whether it's just feelining like crap, or some other symptoms. If I listen to my computer, that is less likely to happen, right?

[mattwave]

To quote AG - "If you haven't been bent, your not diving"

[Pez7378]

To quote AG - "If you haven't been bent, your not diving"

I understand this, but aren't we trying to "minimize" risk? I guess the real reason I would choose to rely on my computer is that I just haven't learned how not to yet, and I haven't seen the benefits yet, and I don't want to experience ANY visible signs of DCS if I can avoid it. Maybe I just shouldn't dive.....


Yeah right, that will never happen I'm sure I'll learn what I need to know, when I need to know it.

[BDub]

And, why is it better to stick with the computer rather than figure out which of the above tables works for you.

After reading this again, another thought came to mind. Now it could just be my lack of understanding but in order to figure out Which tables work for me, I'd also have to learn which ones don't work for me, which means experiencing DCS whether it's just feelining like crap, or some other symptoms. If I listen to my computer, that is less likely to happen, right?

You don't have to go out and try all these different profiles, Chris. Just pay attention to what your body is telling you. If you feel like crap after a dive, don't just accept it as a bi-product of diving and disregard it. Think about the dive...your depth, bottom time, were you cold, your ascent rate, deep stop depths, time spent at the stops, etc and you'll figure out what works for you.

I found out very quickly what didn't work for me, and started playing around with my ascent/deco profiles (they were very "lopsided", leaving quite a bit of room for experimentation) until I found one that worked for me. And yes, there are computers that would have been happy with the profiles that made me feel like crap.

[LCF]

If I listen to my computer, that is less likely to happen, right?

It depends. What Doug said is the key -- What algorithm is your computer using, and how is it organizing your stops?

For no-deco diving, the "conservativism" of the algorithms varies wildly. We had a dive at Catalina last year where my friend's Aeris computer never went into deco, and Peter's Suunto gave him 20 minutes at 10 feet. For decompression diving, different programs will give you VERY different profiles. Dissolved gas models will send you as shallow as the gradient allows, and hold you there for as long as necessary. Bubble models will tend to start stops deeper and use a gentler curve. There are computers that use each of those approaches, and instructors who use programs that generate different stop times and depths. It's pretty clear that individuals vary in their susceptibility to (or ability to perceive) mild DCS, and people often say that they have had to adjust the output of whatever program or computer they are using for decompression, to make themselves feel better after a dive.

So the simple answer is, if you are doing no-deco diving and allowing a computer to tell you how much time you can spend at depth, you are likely (but not guaranteed) to escape clinical DCS (this is, of course, assuming ascents are executed properly, with controlled rates). Remember that the computer has no way of knowing how much nitrogen you have actually absorbed, or how efficiently you, individually, offgas; it can't know your hydration status, or your workload at depth, or your fitness level, or any number of other factors that can play into DCS symptoms.

I'm not trying to discourage anybody from using a computer. I just think too many people think the things are doing something they aren't.

[Joshua Smith]

Josh, are you using VPM, like in a Shearwater? What GFs are you using? 30/85?

RIchard best referred to GFs (developed by GUE in Deco Planner, ironically) as "kludge" factors to force deeper stops. I've monkeyed with them a bit using VPM (Freeplanner and V-Planner) and can kinda generate profiles I like to dive.

My typical 150 feet for 20 minute profile would have stops starting at 110 feet for 1 minute and continuing up to my gas switch. Then, 3,3,1,1,3,6,4 to the surface (although 2,2,2,2,3,6,4 is something we've been debating moving to). This gets things a little deeper in terms of first stops and shape of a curve than pure VPM with GFs.

Can you post a screenshot of some of your profiles? Might be fun to compare notes.

Yeah, I have the older Shearwater GF, affectionately known as the "brick." Right now, it's set at 15/85- which, I'm finding, works pretty well. For deeper stuff, I stick to the tables- I'll post a schedule later for discussion, but I don't have the d/l kit for the brick.


EDIT- I just now realized this was in the UTD section- I apologize if I said anything that goes against the grain! I didn't mean to start talking about CCRs and computers in here!

[loanwolf]

Decompression is very well known about it has been studied for over 100 years. The human body is not static it is a fluid environment that is changing form day to day. What works one day may not work a few days later depending on you physical and psychological state. What works for you may not work for your friend. So a fixed variable will work for everyone. Thus we have the tables of today which are bases on statistics. This many dives with this many hits. The tables and algorithms are based on the safest of these statistics. If you want to push it use old Navy tables (pre 1984) we used to use they are based on a 22yr old fit diver that is doing 30 to 40 hrs of bottom time a week 40 weeks a year. These will get you out of the water faster but will probably bend the hell out of most recreational divers.

Computers are a great advantage but one should always have backups to them. Especially an integrated computer for OC or CCR. I Run integrated for both OC and CCR when I dive. My CCR reads live what PO2 I am breathing and what my depth and time are and calculates the best deco for the dive. My OC rig reads my work of breathing, depth, time, and my mix and calculates my deco on that. I run a GF of 15/85 on my SW and a CF of 2 on my Cochran’s. Most good computers keep track of your RN levels for repetitive dives and will start to penalize you as you dive more repetitive dives. They will also in some cases keep track of you CNS and OTU levels as well. Yes it is good to plan your dives and to know how to use tables but if the tools are their why not take advantage of them. It allows you more freedom to do things differently you are not stuck to a strict regiment. And you do not have to try to recalculate your deco on the fly. Which if you are heavily task loaded or dealing with an emergency is almost impossible for most people to do.

[CaptnJack]

Computers have very high precision. But completely unknown accuracy. In DIR-UTD we plan deco differently so that we don't all need to have the same computer. I'm diving with people up and down the West coast and in MX and we are all doing deco the same ways. That would not work if I had a Shearwater and you had a Cochran.

Its not precise. We discuss the personal "fudges" beforehand. We all dive exactly the same (most conservative) plan.

I would like someone to clarify this new UTD/DIR forum cause we have alot of posts here from constant ppO2 CCR computer users and I think its muddying the OPs waters.

[Sounder]

One of the best sound bites I've heard that applies to this discussion is "deco is an art, not a science." It's very individual in both philosophy and physiology.

[Pez7378]

What algorithm is your computer using, and how is it organizing your stops?

I have the Suunto Vyper which uses the RGBM. I think it favors a more gradually curved ascent? I guess I'm just not at that point where I'm out diving my computer. But I want to explore the alternatives. Discussions such as these are very helpful to me though. I guess it just re-inforces some of what I've already been taught, and some of what I want to learn.

It wasn't too long ago when I thought Nitrox was Black Magic VooDoo.

[CaptnJack]

The Suunto uses "RGBM" but not really. They kinda bought the name more than the algorithm. Its basically Buhlmann and a very conservative iteration of that.
No deep stops
Major penalties for repetitive dives

Alot of us have used them in the past, they work fine for local recreational dives. Not a deco computer though.

[Joshua Smith]

I would like someone to clarify this new UTD/DIR forum cause we have alot of posts here from constant ppO2 CCR computer users and I think its muddying the OPs waters.

Absolutely. As I pointed out above- I usually hit the "new posts" button on the front page and scan- I didn't realize this thread was in the UTD/DIR section until I had 2 posts up.I'm the one who brought that stuff up in here, and I apologize again- still getting used to the new site.

Non-DIR types, CCR divers, etc- lets either stay out of this discussion, or at least not let it turn into a computers/ ratio debate, OK?

[mattwave]

The Suunto uses "RGBM" but not really. They kinda bought the name more than the algorithm. Its basically Buhlmann and a very conservative iteration of that.
No deep stops
Major penalties for repetitive dives

Alot of us have used them in the past, they work fine for local recreational dives. Not a deco computer though.

That's double true, it has been speculated that Suunto and Mares have paid Weikne hundreds of thousands to utilize his RGBM algo, but still base their platform on a penalty based buhlman profile. Which is not reccomended by either manufacturer for diving beyond NDL limits.

All covered in my new Free Computer Diving Seminar!

[BDub]

The Suunto uses "RGBM" but not really. They kinda bought the name more than the algorithm. Its basically Buhlmann and a very conservative iteration of that.
No deep stops
Major penalties for repetitive dives

Alot of us have used them in the past, they work fine for local recreational dives. Not a deco computer though.

They also give you penalties for deep stops too. It wants you up in that 22'-15' range quick. A slow ascent and deep stops just pisses it off, giving you quite an obligation when you get to it's "happy zone".

Not a big deal, especially at the recreational level, but again, you need to keep in mind that what works for your computer may not work for your body.

[loanwolf]

I have dove with lots of DIR divers and with many different mixed groups. Especially over the last two month long trip up and down the west coast. I have found very little difference in Tech computers at the end of the dive, with the exception of a few. Maybe a minute of two is all. But many do have differences in deep stops. That is why i like running two different computers. One is integrated the other is not on all my dives. They run different algorithms so I can choose to do the deep stops one puts up or get up to warmer water if I am cold. But I find they clear about the same time each time I dive. and if two computers are saying you are good to go then I am ver competent in that.

I dive both OC and CCR sorry if i have treaded on waters i should not have i did not look at were this was posted either.

[Pez7378]

I would like someone to clarify this new UTD/DIR forum cause we have alot of posts here from constant ppO2 CCR computer users and I think its muddying the OPs waters.

Absolutely. As I pointed out above- I usually hit the "new posts" button on the front page and scan- I didn't realize this thread was in the UTD/DIR section until I had 2 posts up.I'm the one who brought that stuff up in here, and I apologize again- still getting used to the new site.

Non-DIR types, CCR divers, etc- lets either stay out of this discussion, or at least not let it turn into a computers/ ratio debate, OK?

I'm cool with it. I can tell the difference between OC and CCR. Although it seems this is all related to various Deco theories, I'm really just trying to wrap my mind around diving without a computer.

If I get too confused, I'll cry foul.