Ratio deco for ccr?

PeterN

PeterN

Active Member
Aparently Clare does it, others might. I didn't think it worked for ccr.

The two senarious I am interested in are, the standard bounce dive with a predictable bottom, and travel in a cave. The first might be easy? The second does not seem at all a good application?

On a particular cave project we have up here, my standard ocean tables to back up the Shearwater will not work. We would do well to have an allternate plan.

Thanks,

Peter
 
Peter. My buddy and I have done well over 1,000 dives using ratio deco. I've not once used a computer for a deco dive.

All our training was based on it and all dives from 6-90 meters and 30mins to 360 minutes in ocean and cave. I would not recommend it as a strategy to anyone else especially if they don't dive with a team on the same page but to claim it doesn't work is a bit wide of the mark :)

Ratio deco is not what you read on the Internet nor is it voodoo. The only posts I have ever read about it on forums have, without exception, been incomplete or incorrect bit for obvious reasons I do not wish to set out another version.

The benefits of RD are the ability to forward plan in water with regard to gas and cave deco. For example, I (normally ;) know what route I will take out of a cave so can track forwards and work out future liabilities. You would be right that square profile wreck tables will not be helpful.

I did some dives with NEDU guys a couple of years back and found not a great deal of difference.
 
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DIR ratio deco might not work but sit with your deco software for a few hours and you'll spot patterns occurring. It isn't hard to fit it round some simple rules.

I've got my own set for the gases I use and that's how I came by them. I don't dive on it but I do use it as a mental cross check for what my computer is saying and for rough dive planning.
 
I think the two biggest "issue" I have with ratio deco (or at least the "versions" I've had explained to me) are:

I don't exactly trust myself to do the "calculations" correctly in a situation where the smell stuff hits the rotating thingy.

And even more the way it seems to semi-random how and where the deco minutes are "placed" during the ascent. It might not be as random as I think it is and/or it might now matter if a few minutes are placed semi-randomly but it doesn't instil confidence for me.

I'm in no way experienced enough to say whether ratio deco is any good, and certainly I'll bow to Clare's experience, I just know it's not something for me.....

-Jacob
 
Now I don't know two hoots about ratio deco and please keep that in mind. But we talk about using check lists for rebreathers to try and get rid of human error on one hand and on the other some use ratio deco that means you have to be able to do the maths under water so prone to error?
Are those of you that promote using checklists actually dive ratio deco?
Now again it's never been explained to me in a way that I find it easier than computers in case of task load.

Now my questions are what advantages do you have compared to computers?
Also if you use ratio deco do you have a computer backup?

I'm not after a bashing contest but it's just that I don't get the logic...

Envoy***233; depuis mon GT-I9100 avec Tapatalk
 
PeterN said:
Aparently Clare does it, others might. I didn't think it worked for ccr.

The two senarious I am interested in are, the standard bounce dive with a predictable bottom, and travel in a cave. The first might be easy? The second does not seem at all a good application?

On a particular cave project we have up here, my standard ocean tables to back up the Shearwater will not work. We would do well to have an allternate plan.

Thanks,

Peter
Click to expand...

Its fairly simple. For a linear penetration (cave) I use the "six of one and half a dozen of the other" rule. If you are bouncing from 200' or shallower, then remember that 'one in the hand is worth two in the bush' and half it.

Once I get over 200' I dont have a predictable bottom. Especially if I had curry the night before, so Id be more conservative. Remember you are at constant setpoint on CCR, so you can take a 1:1 ratio all the way to the bottom beyond the 45m mark!

For those mathematicians amongst us (This ones for Andrew Ainslie if hes here), the equation for the Ratio Deco CCR continuous setpoint is as follows:

***8747; 1/(cabin) d(cabin) = log cabin + c = houseboat
 
Clare said:
Peter. My buddy and I have done well over 1,000 dives using ratio deco. I've not once used a computer for a deco dive.


QUOTE]

Thanks Clare. Were those 1000 ccr dives?

Like Stuart, I can pretty much conjur up a deco plan for most of my routine dives.

My question was meant to be if there is a way to use ratio deco when we are on ccr, fixed PO2, when as I under stand it, ratio deco was set up for a fixed FO2.

If this can be made to work, even if somthing must be written down, I am curious. Sceptical about the utility in a complicated up down back there cave passage, but that is also where my backup tables and intuition, let me down.

Peter
Click to expand...
 
PeterN said:
Like Stuart, I can pretty much conjur up a deco plan for most of my routine dives.
Click to expand...

Does it need to be much more complicated than this?
I have four simple rules I remember;
For 50m dives, bottom time and deco time are about the same
For 70m dives, deco time is about twice bottom time.
Do half of any deco at 6m on O2.
Wait 10 minutes after your buddies have left the water before getting out. If they're a bit bent, they'll be getting back in, and you know to do a bit more deco.

Rule 4 seems to be the most useful...

Mike
 
[quoted comment removed - GLOC]

A well thought out and measured reply there Monkey. Let's try to keep the comments constructive and respectful of all members (especially those that started the damn forum!#!)

It doesn't make sense to me to use it as a primary deco calc, but being able to do it when everything else craps out or just to double check if you are not sure could be nice.

Sent from my XT905 using Tapatalk 2
 
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mike said:
Wait 10 minutes after your buddies have left the water before getting out. If they're a bit bent, they'll be getting back in, and you know to do a bit more deco.

Rule 4 seems to be the most useful...

Mike
Click to expand...

I love rule #4! I am going to start using this immediately!
 
Clare said:
Ratio deco is not what you read on the Internet nor is it voodoo. The only posts I have ever read about it on forums have, without exception, been incomplete or incorrect bit for obvious reasons I do not wish to set out another version.
Click to expand...
I would be interested in hearing you expand on an explanation that was incomplete or correcting errors. I personally use a computer but enjoy learning other techniques.




Sent from my iPhone using Tapatalk
 
I know that on a dive in 40-50m range I can use approx 1 minute of deco for every 1 minute on the bottom. This means that if I spend 25 minutes on the bottom, then once I have done about 50 minutes in total I will be sat on the line wondering "did I do 25 minutes on the bottom or 30? 30 I think...or was that last weeks dive?"

I find it a useful ratio for chatting about dive times on the boat before the dive, but I rely on my computer, because if my maths doesn't fail me my memory will.
 
PeterN said:
Like Stuart, I can pretty much conjur up a deco plan for most of my routine dives.
Click to expand...


This statement is where Ratio deco... goes right off the reservation. Ratio Deco goes deadly on the NON routine dives.

Case in point. dive to 400 to routinely and simply practice deep water bail out. rebreather shuts down at 350. the diver bailed to a bail out that had a stage 2 failure. the next problem arose when the divers buddy reached for their bail out reg and it exploded when the tank valve was opened. Now we have a double failure at 350. THIS HAPPED IN REAL LIFE.

Now do you think as the mind narrows to handle this cascading problem it becomes resonable to work ratio deco out ????

Ratio deco is a solution to a problem that does not exist.

The dumbest response I got from a ratio diver and this about sums them up, is and I quote "well you know dive computers can make mistakes"
 
Clare said:
Ratio deco is not what you read on the Internet nor is it voodoo. The only posts I have ever read about it on forums have, without exception, been incomplete or incorrect bit for obvious reasons I do not wish to set out another version.
Click to expand...

Please help me out with this. I find it dubious that 100% of the posts about ratio deco are incomplete or incorrect.

Its the Divining rod of DECO. And the sheer lack of adoption speaks volumes.
 
So I've explained, in answer to a question, what I do when diving - and the response was not inline with the spirit and ethos of the community.

Why did I bother?

Bye.
 
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quoted comment removed - GLOC

Do not make this personal, he said something very different..!!

Take the time to tell us how it works and why it works even in a very stressful situation.
For me personal i do not trust the human brain in a panic situation so i always use a wrist slate and a backup computer.
if i have a very big problem and a brain freeze i would like to get out of the water alive.
 
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Until I can get to a computer (on iphone at the moment) to remove the personally abusive comments, thread locked.

CCRx works by having a community providing logical and unemotive arguments. Irrespective of what you think or truly believe, 'laying into someone' on the forum is not on and will not be tolerated.

[edit - comments removed, included quoted comments from subsequent posts - please keep it civil, we all have something to learn. If you think you know everything, Darwin is waiting for you...]

Regards
 
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Monkey said:
Its the Divining rod of DECO. And the sheer lack of adoption speaks volumes.
Click to expand...

I don't think this is true. I think the lack of adoption has much more to do with the lack of understanding and the lack of ability to do math. As a math professor who teaches remedial math at a college, I can absolutely tell you that basic math and arithmetic skills (which are different things) are pathetically lacking, at least in the USA. Even the most simple calculations are taxing for many in the best environment. Now try it under water, under pressure, when things turn to poo, and maybe toss in a little narcosis or CO2 into the mix.

Buhlman and VPM are based on calculations too. But I don't see anyone doing these in their head underwater. I agree that ratio deco has its place and is generally fine when things go well. Good to use as a reality check on a computer or for quick planning on a routine dive. But "when the smelly stuff hits the rotating thingy' (I really loved that one), I would prefer to trust and look at a dive computer that is much more reliable and proven. My handset does a GF calculation based on reading loop gas. My standalone does a VPM calculation based on fixed pO2. As long as they are fairly close to each other in TTS, I know I'm fine. And I would happily use either one if the other crapped out.

YMMV

Ken
 
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