Can someone explain Ratio Decompression?

[Slamfire]

I have read Doppler's article, I have no issues with it apart from the fact that its rather generic, and its hard for even a moderately experienced deco diver to take away an actual plan to utilize.

The author explains that this is by design: "...the real intention of this article is to outline a technique I have taught to interested and qualified divers for several years. It’s not a foolproof way of producing a decompression schedule – there is no foolproof way of doing that – but it has been used without incident in various locations, most particularly in the Great Lakes region of North America, where the water is cold and conditions tough. Bear in mind, what is being presented here is just an outline. There are a couple of steps I have purposely glossed over to “disable” the information."

From your post, I can't tell if you actually understand AG/GUE's/UTD's version or not... Do you have any practical experience to add with ratio deco or are you just attempting to slam GUE/UTD etc people who use it?

Please point out where I have slammed anybody for using RD? Other than the incorrect semantic way of my use of the word 'algorithm', can you please point out anything untrue or inaccurate that I have said with respect to RD?

 

[rjack321]

Correct, but there remains the caveat that it only works with a limited number of inputs.

Without doing a bunch of homework and establishing my own set point and ratio, I can't for example solve for a dive to 140 feet breathing 15/55 and using EAN80 at 30 feet for decompression.

I have never even used 80% before but ever without looking at any software, the side of the VPM/buhlmann GF barn is so wide I bet you could hit it.

 

[Blackwood]

Okay, instead of 140 make it 190.

I may be able to hit the barn door, but I wouldn't try it.

 

[rjack321]

Okay, instead of 140 make it 190.

I may be able to hit the barn door, but I wouldn't try it.

Well that's outside your normal range no?

I guess my point was more, even though the mixes may get a little wonky... If you are at all paying attention, for most dives in your typical range you have a pretty good guess how much total deco you need.

 

[Blackwood]

It is, but then I can't get 15/55 anyway.

At some point we have to really own this, and admit to ourselves that we're basing our well being on theory. We also have to make a personal decision regarding how far off of the 'accepted theory' mark we're willing to stray.

If my nominal schedule is based on using 50% and 100% for deco, using only 80% (ceteris paribus) is too far for me.

 

[rjack321]

It is, but then I can't get 15/55 anyway.

At some point we have to really own this, and admit to ourselves that we're basing our well being on theory. We also have to make a personal decision regarding how far off of the 'accepted theory' mark we're willing to stray.

If my nominal schedule is based on using 50% and 100% for deco, using only 80% (ceteris paribus) is too far for me.

Depending on your perspective, accepted theory is not safe (nothing is). Sooner people accept that most models are just educated guesses the better. Some more or less educated than others, some based more on theory and less practical and vice versa.

I am not about to go diving 15/55 with 80% at 190ft either (min gas would be more than my comfort zone among many other issues). That doesn't mean you have no clue how much deco you've got. I would guess for a 25min @ 190ft you'd have roughly 50mins total, 25mins shaped exponential up to 30ft, then 25mins at 30ft and a little bit more at 20 & 10 to achieve something close to 30/85 GF Buhlmann. My old old copy of decoplanner won't run on vista so I have no way to check tho.

 

[Blackwood]

I'm not even sure what we're [-]arguing[/-] anymore

My copy of iDecoPro at GF30/85 wants an 86 min run time, 32min of which are 30' and above. Would you be 'okay' with your profile? Probably. (Same answer given for doing it 'properly' with 50% and O2).

My point is that I won't plan to use gases that the system doesn't consider. If all I have is 15/55 and 80%, I'd more than likely pass on a 190 foot dive (rock bottom also being the biggest issue), but if I didn't pass, I'd run a desktop profile.

 

[limeyx]

Interesting. Is it taught that way or is that simply a personal decision (250 is far beyond my knowledge base) ?

You can bat it two ways that turn out similar I guess

for a 250 dive you can either
1) use the 2:1 ratio (but with 15/55) with 2 deco gases and add 25 mins to the 2:1 but you have a ginormous RB (so you usually need a stage)

2) Add the 35/25 bottle and use 3:1, and take the 25/25 bottle as 20% of the deco time

anything deeper than 240-maybe 250 and that 2:1 ratio probably isn't looking like such a good idea IMO

In practice, the 120 bottle is more about rock bottom than time, as 20% of 70 min deco time compared to your deep stops from 120-80 isn't much of a time difference.

It really only really sank in to me recently that really for the vast majority of dives, the 70-20 deco is 99% of the "deco" equation, the rest is all about reducing rock bottom to reasonable levels and handling lost/unusable deco gases.

 

[rjack321]

I'm not even sure what we're [-]arguing[/-] anymore

My copy of iDecoPro at GF30/85 wants an 86 min run time, 32min of which are 30' and above. Would you be 'okay' with your profile? Probably. (Same answer given for doing it 'properly' with 50% and O2).

My point is that I won't plan to use gases that the system doesn't consider. If all I have is 15/55 and 80%, I'd more than likely pass on a 190 foot dive (rock bottom also being the biggest issue), but if I didn't pass, I'd run a desktop profile.

I'm just saying that if you are at all paying attention, know the principles of helium and how much (backgas) deco you accumulate at any given depth/time, you can come up with something that might not be ideal but its probably going to get you out alive. RD is just a more formalized set of "rules" to come up with a schedule at basically GF 30/85 for standard gases.

 

[Slamfire]

... are you just attempting to slam GUE/UTD etc people who use it?

I'll echo some questions that Lynne was asking in another forum. Is it my nickname - Slamfire? Is it that my avatar projects an image of somebody hellbent on destruction? I don't intend to change those BTW

Contrary to what you seem to think about me, I am not on a personal vendetta against AG, GUE, UTD or any other agency. The OP asks about RD and I was the first to answer. I provided him documents (I think the 5thDx one was written by AG himself) about RD and even pointing him to where he can get online UTD training on RD. I'd say that is a very modest way of promoting UTD, very far from slamming it.

The vast majority of dives that I do here in west coast Canada are with UTD trained dive buddies. I consider the local UTD instructor a friend. He's helped me out with diving related issues many times. When somebody in the Western Canada forum asked about feedback/recommendations of tech instructors, I've given sincere positive remarks about the local UTD instructor.

I also provided positive feedback about other non-UTD and non-GUE instructors that I also consider friends. My intent and recommendation was that the prospective student talks to them and makes up his own mind. I believe I did something similar in this thread. I presented information about RD and another similar non-UTD/non-GUE deco-on-the-fly methodology. I did not claim one is superior to another. I believe Captain Frank is smart enough to decide what, if any, deco-on-the-fly methodology is best for him.

If you look closely, the differences we've had on other threads are not because you are GUE trained. They are limited to very specific and isolated points.

I do not believe that providing information that goes outside of UTD or GUE constitutes an attack on these agencies. If the agencies are worth their weight, they'll survive in the face of competition. And guess what, I believe they are and, at least from what I see locally, I believe they are growing.