Deco with too less air, options from the book

[jtivat]

why post like that with gases/amounts you would not use? makes no sense and it feels like a set up.
Not a set up but thought it would help to use standard mixes

RD cannot tell you if you have enough gas. only proper gas management can tell you that which of course is also done. when u figure out your gas management, at that point you should know how much you have to safely extend your dive if u need to.

RD will help you do the deco once you have extended your BT by 10 mins if proper gas management allows you to do that.

Well then I really do not see the point I run and take with me tables that do just that and I can spend my time seeing the wreck not doing math.

 

[Rainer]

Well then I really do not see the point I run and take with me tables that do just that and I can spend my time seeing the wreck not doing math.

I don't get where this misunderstanding or fear of math arises. The math is simple. About as difficult as pulling out your tables (and I don't know about all divers running RD, but I *do* have schedules in my wetnotes for the dives I do most often). If it's a dive for which I don't already know the deco going in (i.e. a new depth/BT combination), I'll have the deco calculated during the deep stops before I hit my first gas switch.

We're not swimming around doing deco calculations.

Did school fail to teach people basic arithmetic? Just don't get this math dread. Weird.

 

[gcbryan]

I don't get where this misunderstanding or fear of math arises. The math is simple. About as difficult as pulling out your tables (and I don't know about all divers running RD, but I *do* have schedules in my wetnotes for the dives I do most often). If it's a dive for which I don't already know the deco going in (i.e. a new depth/BT combination), I'll have the deco calculated during the deep stops before I hit my first gas switch.

We're not swimming around doing deco calculations.

Did school fail to teach people basic arithmetic? Just don't get this math dread. Weird.

Just curious but why do you care if anyone understands/misunderstands or has never heard of RD?

 

[shoredivr]

http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html

"We kept a constant depth of around 45m/150 for the elapsed 30 minutes so far, and were just basically floating neutrally buoyant with very little finning while exploring the forward deck area . . .so I made the decision to extend the Bottom Time from 30min to 50min, or hitting MGR/Rock Bottom whichever came earlier."

"I wrote in my wetnotes and communicated to my Buddy, "Re-calculate Ratio Deco 1:1 for 160 . . ." My Buddy signaled & acknowledged okay.[ Lessons Learned: 1) An Error of Omission: I should'vd wrote, "Re-calculate Ratio Deco 1:1 for 160 with Bottom Time 50 minutes. 2) An Error of Commission: Don't place a burden of re-calculating an entire Deco Profile on both yourself and your Buddy especially when you're both narced out-of-your-mind on Deep Air at max depth. At most, just figure out the Deep Stops to perform by looking at your WKPP Table in your wetnotes, then get to your Eanx 50 deco gas switch at 21m/70' and then as the narcosis eases, finally start re-calculating the required profile times needed on your Nitrox 50 and subsequent Oxygen Deco Stops. Better still, use a tech computer with a similar algorithm to your calculated decompression profile for back-up]"

"And now, the Eanx 50 switch and the Fateful Blunder: I signaled seven minutes deco time. My buddy queried back, "Seven?" I signaled again definitely seven minutes. Buddy looks at me with a puzzled face; and this is where it all started to go wrong for me-- with the fist-to-forehead signal, I yielded and gave back control of the Deco Stops to my Buddy. He gets out his wetnotes and starts doing some scratch arithmetic, and then writes out a 4, 3, 3, 3, 4 minutes time sequence for the 21m/70 stop thru to the 9m/30 stop."
"[Lesson Learned: again I had the greater experience utilizing Ratio Deco on this particular dive and should have insisted on taking over lead and captaining the deco; I'm not quite sure why I conceded to this revised profile when it felt all wrong to me intuitively ("Deer in-the-Headlights Syndrome": you're overwhelmed cognitively and fail to act decisively, despite realizing an immediate threat to your safety.]"


Trimix was not available for this dive. The poster is from his profile, experienced in deco and RD. His analysis is that despite having experience in RD and deco beyond what his buddy had, he allowed himself to surrender control of his deco.

This was not an emergency situation, just a change in the dive plan. Yet an error occurred that resulted in a bend. I thank the poster for reporting it, because it illustrates for me that changing a deco plan has its hazards.

Referring to pre-printed deco schedule and contingency schedules would seem have less margin of error, as in one less thing to calculate, especially when it goes pear-shaped.

 

[orange_diver]

Well then I really do not see the point I run and take with me tables that do just that and I can spend my time seeing the wreck not doing math.

a minute or less is spent figuring out the deco if you've deviated from the expected dive plan. plenty o' time for wreck sights.

but on the surface we save tons of time not having to run, print / write out multiple tables "in case of..."

 

[Rainer]

Just curious but why do you care if anyone understands/misunderstands or has never heard of RD?

What an odd question.

In this thread I was directly asked to describe certain aspects of RD, to which I obliged.

In general, I know I was happy to hear about it myself, and can only assume others would be as well. Those people who talked about it weren't looking to "convert" anyone, just as I am not. That said, what's the point of helping to continue to foster ignorance when you can shed some light, especially when asked?

Let me ask you: why do you care to ask me this question?

RD isn't a "better" way to do deco; it's just a better way to do deco for me (and I assume those who also practice it). Lots of methods work (duh). They all have pros and cons. Dive, however, you wish. Learn about other methods. But, please, take the time to learn before harping.

 

[Blackwood]

Still would like to know who/where that photo is from...

Me too.

An example of RD in a non-stressful (albeit deep air) situation which illustrates that things can go wrong calculating in one's head on the fly, with good analysis afterwards.
http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html

That's an example of many things, none of which are Ratio Deco.

 

[Bismark]

http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html

"We kept a constant depth of around 45m/150 for the elapsed 30 minutes so far, and were just basically floating neutrally buoyant with very little finning while exploring the forward deck area . . .so I made the decision to extend the Bottom Time from 30min to 50min, or hitting MGR/Rock Bottom whichever came earlier."

"I wrote in my wetnotes and communicated to my Buddy, "Re-calculate Ratio Deco 1:1 for 160 . . ." My Buddy signaled & acknowledged okay.[ Lessons Learned: 1) An Error of Omission: I should'vd wrote, "Re-calculate Ratio Deco 1:1 for 160 with Bottom Time 50 minutes. 2) An Error of Commission: Don't place a burden of re-calculating an entire Deco Profile on both yourself and your Buddy especially when you're both narced out-of-your-mind on Deep Air at max depth. At most, just figure out the Deep Stops to perform by looking at your WKPP Table in your wetnotes, then get to your Eanx 50 deco gas switch at 21m/70' and then as the narcosis eases, finally start re-calculating the required profile times needed on your Nitrox 50 and subsequent Oxygen Deco Stops. Better still, use a tech computer with a similar algorithm to your calculated decompression profile for back-up]"

"And now, the Eanx 50 switch and the Fateful Blunder: I signaled seven minutes deco time. My buddy queried back, "Seven?" I signaled again definitely seven minutes. Buddy looks at me with a puzzled face; and this is where it all started to go wrong for me-- with the fist-to-forehead signal, I yielded and gave back control of the Deco Stops to my Buddy. He gets out his wetnotes and starts doing some scratch arithmetic, and then writes out a 4, 3, 3, 3, 4 minutes time sequence for the 21m/70 stop thru to the 9m/30 stop."
"[Lesson Learned: again I had the greater experience utilizing Ratio Deco on this particular dive and should have insisted on taking over lead and captaining the deco; I'm not quite sure why I conceded to this revised profile when it felt all wrong to me intuitively ("Deer in-the-Headlights Syndrome": you're overwhelmed cognitively and fail to act decisively, despite realizing an immediate threat to your safety.]"


Trimix was not available for this dive. The poster is from his profile, experienced in deco and RD. His analysis is that despite having experience in RD and deco beyond what his buddy had, he allowed himself to surrender control of his deco.

This was not an emergency situation, just a change in the dive plan. Yet an error occurred that resulted in a bend. I thank the poster for reporting it, because it illustrates for me that changing a deco plan has its hazards.

Referring to pre-printed deco schedule and contingency schedules would seem have less margin of error, as in one less thing to calculate, especially when it goes pear-shaped.

As another poster has already said, while this dive was many things (few of them complimentary) it was not an example of Ratio Deco. Read a few more of the posts and you will get the gist. Using a specialized tool for anything other than the purpose for which it is specifically intended is not the tools fault if the tool doesn't do the new job. It is the users error in using a specialized tool in a fashion for which it was not intended. Consider the brain surgeon using a table knife.........

 

[Rhone Man]

I can't imagine that I would ever practice ratio deco, but I am always interested in learning about new things, and plus I am a bit of a maths geek, so forgive me if I ask questions that have already been answered in the thread:

1. Is ratio deco used as a planning tool, or is it always used at the end of the dive to calculate/verify the deco obligation?

2. I can understand the "why use computers instead of your brain" philosophy, but my understanding is that for ratio deco you break your dive down into 5 minute segments and work out the average depth for each segment; surely it must be easier to have a computer track this than try to continually monitor and keep all that information on your slate or in your head, even if you ignore the algorith/calculation that your computer gives you?

3. If the basis of the ratio deco is that you have a set point to start from, and calculate your total deco obligation by working out from the set point, wouldn't it be sensible to break this down into table form? The calculations (as explained in this article, which was the most readily understandable that I found) seem easy enough sitting at my desk - but I imagine if you are cold and tired and being jerked on a line in a heavy swell, the risk of error increases...?

4. Doing the maths (as I understand it) and comparing again deco planning software, ratio deco seems to give you relatively somewhat longer decompression profiles...?

5. Has there ever been any published independent review of the ratio deco algorithm by an industry body or academic institution as against other more established decompression algorithms?

Thanks for taking the time to answer.

Other thought: should this discussion on ratio deco be split off by a mod into its own thread?

 

[Rainer]

1. Is ratio deco used as a planning tool, or is it always used at the end of the dive to calculate/verify the deco obligation?

You can plan the dive, however, you want. In our T1 class, we used DecoPlanner. I also have a copy of VPlanner. Once you realize the similarity between the profiles you're generating with RD and the desktop software, you can use either for planning. RD is used in the water to verify the deco against the dive actually done.

2. I can understand the "why use computers instead of your brain" philosophy, but my understanding is that for ratio deco you break your dive down into 5 minute segments and work out the average depth for each segment; surely it must be easier to have a computer track this than try to continually monitor and keep all that information on your slate or in your head, even if you ignore the algorith/calculation that your computer gives you?

Calculating an average depth is not difficult. Baby steps. You practice in the shallow end before going deeper. If you are doing mostly square profiles (wrecks), it couldn't be easier.

3. If the basis of the ratio deco is that you have a set point to start from, and calculate your total deco obligation by working out from the set point, wouldn't it be sensible to break this down into table form? The calculations (as explained in this article, which was the most readily understandable that I found) seem easy enough sitting at my desk - but I imagine if you are cold and tired and being jerked on a line in a heavy swell, the risk of error increases...?

I didn't bother to check the link, but the calculations are so mind-numbingly easy, you don't need to look in your notes. That said, many of us nonetheless jot down schedules as well, if you want the sanity check. Memorizing the algo is easy. You also have a team to check errors against. You've also worked the numbers before hand (assuming no significant modifications to the schedule). You've also likely done similar dives. Remember, RD assumes standard gases, so you aren't getting new schedules based just on what you happen to be breathing that day.

4. Doing the maths (as I understand it) and comparing again deco planning software, ratio deco seems to give you relatively somewhat longer decompression profiles...?

Seems to be right in line with the schedules I get from DP and VP.

5. Has there ever been any published independent review of the ratio deco algorithm by an industry body or academic institution as against other more established decompression algorithms?

RD isn't a deco theory. It's just form fitting existing algos (that assume deep stops, an oxygen window, etc). It's like asking has any industry body or academic institution published independent reviews of the Rule of 120 against the more established US Navy Tables.