Ratio deco for ccr?

[Mr fish]

That or it really doesn't work all that well.



It has been an interesting debate, even if off topic for most of its course. I was hoping one of the anointed GUE members would have more directly commented towards your original inquiry. I'd like to know as well if it can be worked into a set PO2 paradigm, for academic reasons. In practical application however, I will march on with multiple computers and a brace of contingency tables.

just run a ccr table 1.3 . then run same table for oc say 1.2 or 1,3 back gas and 1.6 ppo2 first deco gas , last stop 6m 1,6 ppo2 2nd deco gas

i used to dive with breather guy s running 1.3 , and id do same or less deco for same bottom time oc , if they just sat on 1.3 all the dive ,

o2 will average out even on oc

 

[Igor]

..

 

[Mr Walker]

Nils, i think you are trying to pick a fight ? :chuckle: I don´t thing anyone will bite on that one though.

Actually no, and I know you know it, right? This thread isn't going anywhere right now so I'm just trying to be funny. And there is no fun without and edge, is there?

/nils

 

[Deep_Six]

Ha, I just sold away a Halcyon HID light that I'd had for quite a long time this very morning but it wasn't because it was a crappy light.

And yes, ratio deco can work, of course it can! And does. What's your point?

ps. May the GUE be with you! :luke:

 

[Deep_Six]

just run a ccr table 1.3 . then run same table for oc say 1.2 or 1,3 back gas and 1.6 ppo2 first deco gas , last stop 6m 1,6 ppo2 2nd deco gas

i used to dive with breather guy s running 1.3 , and id do same or less deco for same bottom time oc , if they just sat on 1.3 all the dive ,

o2 will average out even on oc

That's well established and has nothing to do with ratio deco, so....

Uhm, and before this goes further, I have no dog in this fight. I've know all "the players" since the mid 90's and was shown ratio deco before it had a name, I didn't think it earth shattering then and certainly don't now. Just because I can walk from Manchester to Plymouth, doesn't mean it's the best way of delivering milk!

I gotta go :bigdump:

Cheers!

 

[lizardland]

I think you have to be a GEU insider to understand the knowing hints that were dropped about standard gases.

I'm not a gooooeeeey diver so not sure how they do it. My method uses a standard helium % of 50'ish and up to 60m as that's the majority of my diving. I take my base point as 42m. At that depth then more or less every minute of bottom time is a minute at 6m. Every 3m either way is 10% e.g. 42m = 1x BT, 45m = 1.1 x BT, 48m = 1.2 x BT, 39m = 0.9 x BT, 36m = 0.8 x BT. It's easier to work out than it sounds. Intermediate stops are simply proportions of the the final 6m stop time.

It's over-cooked by a bit but it's near enough. Sit with some deco software and the relationships appear.

 

[Mr fish]

That's well established and has nothing to do with ratio deco, so....

Uhm, and before this goes further, I have no dog in this fight. I've know all "the players" since the mid 90's and was shown ratio deco before it had a name, I didn't think it earth shattering then and certainly don't now. Just because I can walk from Manchester to Plymouth, doesn't mean it's the best way of delivering milk!

I gotta go :bigdump:

Cheers!

ratio deco? , you asked about a fo2 and a fixed ppo2
for deco . if a gue oc /fo2 voodoo would work with a fixed ppo2 and i think iv shown it would / could ,

no dog in the fight my self or milk to deliver, i,m a computer man my self , about 2.5k worth

 

[Daffy]

Lamont had some input that was on topic.

Unfortunatly I can't see how it works. Hopefully he will explane it though.

I have an example dive that i am preparing for.
Tx 10/60 SP 1,3
15min@30m, 10min@50m, 20min@80m, 10min@50m 15min@30m
Runtime is 205min

If i take the average depth
70min@50m
Runtime is 180 min

25 minutes skipped deco is to much for me.

I am using RD as a "backup computer". I do not necessarily think there is anything wrong with your approach of using a redundant computer though as long as there is a reasonable underlying understanding of how decompression works. It´s just that i have been diving RD successfully for some time and i feel it works and i do not see the need for a second dive computer at the moment. Fair enough?

I dont know if you calculate different than Lamont, but otherwise i think those 25 minutes are a pretty good reason.
Or is there a way to use RD for these kind of dives?

 

[Monkey]

Personally, I'd love to hear someone with Clare's experience explain what the process is, but I can understand why she 'ran away' as you so unhelpfully described it. Sadly, when people with Monkey's blinkered attitude are happy to pile-in with personal vitriol, the debate gets stifled before it can get going.

Sorry if you think its personal. I drive home a point, thats all. I am far from the first person to stifle the debate about RD.

I would love nothing more than to be proven wrong on my point of view. I Would readily accept it.

but it would seem that every time I have had this conversation with some one here, burgerworld or real world, I am either unaware of the secret code, handshake or missing some sort of secret decoder ring for me to get any answer that does not defy logic.

I would glady accept any private converstion with any one who can nail down why this makes sense.

 

[Daffy]

I would not use a RD on that profile. There is a range of profiles and bottom times that it works on. Get out of range or not using standard gases it does not work very well.

Exellent, good you where not the fist one to answer, then all this debate would be over in no time.

So basicly the answer to the OP Q is, if your profile is eratic enough for tables not to work, RD won't work either.

I was actually hoping there was a way to predict future TTS that also included the return. I, like Randy, are not too worried about the deco but more if the B/O will last. At the moment I use the +5 feature of the SW and an additional fTTS +10 on my OSTC to spot patterns. Together with remembering what max TTS i can have before turning the dive it works reasonably well so far. But this is only because I know or have good estimates of what the profile will be.

But going in totally blind as to what to expect, how to know where to turn in order for the B/O to last?

 

[GaryL]

I haven't gone through all these posts but how do you work out bail out TTS on multiple cylinders using RD, if you've bailed from a dive using RD on the loop. Seems overly complicated integrating them and why would you do one without the other. For me, unless you know RD for loop and bail it's pointless but if you do plan to use both it's an added complication in a stressful situation and further problem waiting to bite. Nice idea but for problem management I don't see any benefits. Computer or slate for me.

 

[Clare]

Edited. Hour of my life wasted on that one.

 

[ebt]

For me, unless you know RD for loop and bail it's pointless

Why do you need both? Usually if you carry appropriate bailout gases, the ccr schedule actually ends up being a bit longer. Sounds bizarre, but its true.... run the numbers yourself

 

[lamont]

Unfortunatly I can't see how it works. Hopefully he will explane it though.

I have an example dive that i am preparing for.
Tx 10/60 SP 1,3
15min@30m, 10min@50m, 20min@80m, 10min@50m 15min@30m
Runtime is 205min

If i take the average depth
70min@50m
Runtime is 180 min

25 minutes skipped deco is to much for me.


I dont know if you calculate different than Lamont, but otherwise i think those 25 minutes are a pretty good reason.
Or is there a way to use RD for these kind of dives?

That's the kind of profile where depth averaging alone doesn't work very well. If you had this instead:

15min@40m, 10min@50m, 20min@60m, 10min@50m 15min@40m

It probably works much better since its smoother. Or if you had this which is just a quick spike somewhere:

15min@40m, 10min@50m, 5min@80m, 10min@50m, 15min@40m

Neither of those are dealing with "ratios" though, so those are just depth averaging. Your profile looks like an example of where depth averaging is fairly bad.

Assuming that the symmetry of your profile is because it's in a cave, then you can roll your own ratio deco by running profiles like this:

15min@30m, 10min@50m, 10min@80m, 10min@50m 15min@30m
15min@30m, 10min@50m, 20min@80m, 10min@50m 15min@30m
15min@30m, 10min@50m, 30min@80m, 10min@50m 15min@30m

Then pick a "setpoint" (unfortunate collision of terminology) around what your 'typical' profile is, and you determine a relationship between how many more minutes of deco you need based on the length of the bottom time. At 80m its going to be close to 2 minutes more deco for every minute of bottom you spend in the 80m segment. You'll probably award 1 minute of that to the 6m stop and 1 minute between 21m and 9m.

As your decos get longer you'll need to adjust the time moving from 30m to 21m and it'll eventually start to break down as you get too far away from your "setpoint".

What you're doing is very similar to approximating sin(x) = x which works to 2% accuracy in the range [-0.5,0.5]. But is obviously very bad near, say, 6.

That's really all there is to it, its just linear approximation, after noticing that there's a pattern in similar profiles.

There's also a practice that GUE divers tend to use which is "linearized deco" which means that instead of a profile full of random numbers to memorize you divide the deco up into phases where the stop times are the same. So for example (apologies for imperial measurements, but I don't have the time to convert this:

15 min @ 330' (10/70)
330 -> 240: 30 fpm (3 mins)
240 -> 190: 20 fpm (3 mins)
- switch to 21/35
190 -> 120: 1 minute stops (7 mins)
120 -> 70: 2 minute stops (10 mins)
- switch to 50%
70 -> 20: 5 minute stops (25 mins)
- switch to O2
20 -> surface: 30 minutes
6 mins slow ascent to surface

(don't ask me how to do the ratio deco on that, the diving there is a bit over my head, but that's a good example of linearized deco, and hopefully heads off misunderstandings suggesting that GUE teaches a straight linear profile all the way to the surface or something...). The basic idea here is that once you're driving a gradient as long as you don't overstay too long it doesn't make a whole lot of difference where you award the minutes for stops between 70 and 20 and so linear is easier to remember. Of course this is holding you "deeper than you should be" and you're using more gas, so when I've had issues on dives I've moved time from deeper stops shorter "on-the-fly" to get shallower and conserve gas when that was important.

There's weaknesses to all three of these principles: depth averaging, ratio deco, and linearized deco. But what is taught is that you apply them where they make sense, and GUE definitely teaches that deco planners should be considered more authoritative than any of these principles.

And like I said, I'm also running with a computer in "parachute mode" these days due to some of those weaknesses...

 

[Igor]

I genuinely do not wish to try to teach deco on the Internet.



Ratio deco became shorthand for the AG wreck diving deco patterns. They work only with a set range of bottom time and on standard gases although you can come up with your own patterns. When people report confidently on Internet forums that they have read up on RD that tends to be ehat they have read.

When I talk of ratio deco, like most I know who cave dive, it is not a simple translation of the AG model. Longer durations and sawtooth profiles make the original taught simple model irrelevant. This does not mean however that deco using planned ratios is not possible and the benefits that will bring addresses your question as to how to plan accurate tts and bailout.

Again, whilst not wishing to teach deco in the Internet, in the example used above you cannot include all the time above 30 to bring your average shallower. I would calculate the run time on this to be 195 minutes so we would not be that far out depending on what parameters you choose. Delaying at any stage of the dive affects the run time proportionately until you hit 35 mins at max depth on that one. It's similar to a dive I've done, without a computer in the water as my RB at the time didn't use one. That dive was planned, run on RD and aborted due to extrapolating RT forward and realising our max TTS had been reached due to slow progress.

With regard to all the comments about retarded or Coolaid, or death wish. I am as keen to come home as the rest of you. My post above which led to Monkeys vitriol clearly stated I really do not recommend this approach as a general tool for the majority. I am not seeking to persuade anyone to adopt ratio deco so stop acting like you are being personally affected by MY choices. The question was posed as to whether it is possible to run RD on a CCR in a cave and I of course answered yes as that's what I do.

I've had PMs asking me to teach this stuff - or explain in more detail. There are numerous posts in this thread alone stating, in a passive aggressive macho bullshit manner, that if it can't be taught or explained on an Internet thread then it doesn't work. The ratios I use in cave diving started to be developed on my full cave with Jablonski and have been evolving over the years in between, informed by diving, reading and talking to peers. I couldn't explain it in one post even if I wanted to. That doesn't mean it is complicated on any one dive. Hoffi said it well when he stated deco is really not that complicated.

For the sake of clarity, who stated that I don't have tables available should the dive go way off reservation are making an incorrect assumption. My wet notes have comprehensive tables. If I need to look stuff up I will. Most of the time though, even if things go wrong, you really only have to know where your first mandatory stop is and you can get things back into line.

To recap. I don't need a calculator to work out that the newspaper vendor gives me the right change. Deco really can be that simple. Would a calculator give me the right answer? Of course. It would also work it out to nth decimal places but if I only have coins there is no point in knowing the fractions of a penny it costs per page. You will not, using RD, work your deco out like a computer. However, for me the knowledge that it gives me at all points in the dive are invaluable and for that reason I enjoy using it.

I've also enjoyed watching the SW on the JJ. It has a few different ideas to me but to be honest the outcomes are really not that different at the end. Does make me laugh though when I'm 60 odd minutes into a cave and it is telling me TTS of a few minutes. RD will tell me how much deco I'll need to do when I get back near to the exit. That's what I need to know.

Like most divers I've had things go wrong on dives. There may be a minute or two while you swear or clench or whatever. I had a dive where I was incapacitated by hydrogen sulphide and was out of it for a long time. But remember, I do not advocate solo diving in any form. If you AND your team really can't get it back together then I'd not recommend a computer - I'd recommend another hobby. If you don't have a regular team then again RD is not for you.

Finally. rule 4 - wait and see if your buddy complains of a bend - used it for years. A word of warning don't use it with Lundgren or Jablonski (or Ingmar I hear). It will hurt.

A note of caution. There really is no need for the aggressive macho crap on here. It may be a cultural thing but I don't think so as most US citizens I've met have been polite, charming snd decent. If you met me in a bar we would talk these things through and I doubt very much that the aggressive alpha male approach would surface. However, if it did, I'd make a polite exit and go find someone more intelligent or articulate to talk to. I behave the same way on the Internet and if that is taunted as 'running away' so be it.

Thanks for a good post Clare.

What strikes me in this thread is how most seem to perceive decompression. This is also my personal experience being around divers. The perception is that if you do not follow your computer precisely you will get bent and dead. Some divers focus on this rather then focusing on more important issues such as breathing toxic gases and other rebreather risk etc.

The fact is that decompression is a very in-exact science. You have a set of minutes that you have to spend give or take but there is a pretty big ****ing lea way where you spend them. You can and should adapt your decompression to conditions. I could for example opt to spend a bit more on shallow stops (6-15m) and cut the deeper stops a bit short if a thermocline is present that i can take advantage of. In rough surface conditions i will cut 6m stop a bit and add to 9-12 instead.

Most people seem to forget that the major player is physiological factors not mathematical theories. Your fitness will play a major role as well as temperature etc. Your brain can adopt to this better then a fixed algorithm from a computer. First step is get your ass in shape, then you ponder the theoretical theories.

I have been Trimix diving since 1993 and back then we shaved the tables until we got bent and then we padded a bit on that and wheeee we had a "perfect" table for the specific profile. This is a very stupid thing to do (monkey jump in here ) but thats what i did and i do not regret it. Computers have progressed and the recent models like the predator are reliable with great user interfaces. Use them to their advantage but remember decompression is not set in stone and have an underlying understanding of deco. Do not just jump in and rely on the computer. Plan the dive with RD or a table, plan your minimum gas etc..

 

[Daffy]

I would calculate the run time on this to be 195 minutes so we would not be that far out depending on what parameters you choose. Delaying at any stage of the dive affects the run time proportionately until you hit 35 mins at max depth on that one.

Okay, fair enough. You plan the dive ahead by some other means than I do and decide you can deco 10 minutes less than me. We would not be a team, because I like long decos and are a true follower of rule 4:yippee:, but I guess you would be fine too.

But since this is an exploration dive and you do not know ahead what the profile will be like, how do you know how much to increase your average depth? You swim around doing calculations all the time to know if the B/O will last based on the changing topography?

I have problems calculating B/O needs for just NDL dives on the fly. I have to average and estimate, and then write up the gas needed home on cookies when I make nav decisions. Otherwise when I come back to that place and want to go in another direction I can***8217;t be sure if I remember that places location within the B/O umbrella or have mixed it up with some other point.:uhh:

To do all that on a deco dive while taking into account stops and also calculating the deco in the head is just baffling. It is three separate and simultaneous calculations running in brain the entire dive.

I don't know what to say, how do I learn this?

 

[Daffy]

At 80m its going to be close to 2 minutes more deco for every minute of bottom you spend in the 80m segment. You'll probably award 1 minute of that to the 6m stop and 1 minute between 21m and 9m.

Well actually it is more like 5 min on my computer but i get the point. This is usually what i do when i plan my dives. Or rather, I figure out how long I can possibly stay with my B/O and then dial it down to whatever deco i am comfortable with.

This is somewhat easy when planning the dive and knowing what to expect.
But sometimes when trying to go to unknown places there is something in the way or it just stops. There might however be alternatives to explore at different depths. But at least i cant hold all those different scenarios in my head so i need to turn and come back another day. Would just be nice to have some method of recalculating instead.

 

[lamont]

Well actually it is more like 5 min on my computer but i get the point. This is usually what i do when i plan my dives. Or rather, I figure out how long I can possibly stay with my B/O and then dial it down to whatever deco i am comfortable with.

Yeah, I can't think deco in metric, and I was sitting at the dentist's office waiting and typing that out and fired it off when I got called earlier than I expected so I didn't get a chance to proofread.

The basic point, though, is that all of these are just approximation tricks to make some simple math come out to agree with what the deco planners tell us.

I have run into people whose understanding of deco comes entirely from RD and they follow RD religiously and would trust RD over a computer or a deco planner. I don't believe that correct, and its certainly not what I was taught in GUE courses, and the course lecture materials are pretty clear on that.

Again, the analogy that makes the most sense to me is from physics courses in college where if you know (via symmetry or something) that the answer to a problem is that x is nearly 0 you can substitute x for sin(x) and solve the problem and you'll often wind up turning college level math into high school level math. If the answer you get is close enough for your purposes you can run with it, or you can use the simplified answer as a double check for the results you get from crunching through the problem without the approximation.

Ask any physicist, "why did the chicken cross the road?" and the answer should begin with "first, assume a spherical chicken of uniform density..."

 

[PeterN]

I genuinely do not wish to try to teach deco on the Internet. I'm going to answer a few questions and pick up on a few posts to avoid having to answer PMs. To those who sent them, apologies but I have no intention of running a crash course in this for anyone.

.

Clare, thank you for taking the time. Perhaps my question was too ernest, but I am interested, and clearly lack the communication skills to ask it in a more acceptable manner.

I was not asking to be taught deco on the internet.

To me, it is sad that you feel you must qualify your response by inserting your considerable experience and qualifications. Interesting, but hardly OT.

I derive from this that the RD that the locals use is not at all what is practiced on the bigger dives. Thank you for that.

As I am a survivor of my own deco tables in the bad old days, I am only too aware that many aproaches work. I submit that we all are.

As for our rude American friends, I will take the passion and forthrightness of a Monkey over what some might describe as passive aggressive or even pompous .

I am not smug. I am the even harder to take golly gee whiz. I do this because I am aware of just how much I am pushing it and I am trying to develop some best practices for those few years I have left.

I have learned a lot on this thread. Much of it not expected. Thank you all who have contributed.

Peter

 

[Robert]

I use 1*computer (new - inuse less than a year), with D-timer+tables (and an understanding of tables - see below) as backup. Except if I'm doing it the other way around, with the computer being used as the backup.

I see computers, tables and ratios as all having advantages & disadvantages, so I prefer to have more than one type of system available.

My main issue is that there seems to be a growing number of people out there who have only ever used computers from dive 1, and don't have much if any understanding of decompression. As a couple of examples:

- on a (mostly) non-deco liveaboard years ago, someone came up and asked if I thought he should do his 7th dive for the day. He was a bit dubious about it, but he was thinking about doing it anyway because his computer seemed to think it would be OK. I talked him out of it.

- in Truk the trip before last (prior to getting the computer), I forgot my wetnotes on the second dive one day. I'd been diving similar profiles for a week or so beforehand, and decided it would be 38 minutes deco. I took 38 minutes (plus 10 mintes for safety that I was adding to all dives on that trip) and split it up in a manner I thought was logical. After the dive I got onto the laptop and had a look at what I should have done. It was 37 minutes - (I'd done the extra minute at 9M), plus the safety time.

So far, the computer has worked for me, but I still consider it to be somewhat experimental,

Thanks,
Robert