Dotf

prharris · February 16th, 2006, 01:24 PM

Ok,
I've check with an admin and it's ok to post this here

It's a DOTF question. We all know AG has published his take on it so it's in the public domain, but I also appreciate the feelings of those Tech 1 peeps who were asked not to divulge what they learnt on the course.

Anyway, one of the stipulations/rules/recommendations for DOTF is that you have the correct gasses, and these match with the GUE recommended gasses, fair enough!

Now, some of us that have managed to sneak on here have devices that will mix a supposedly perfect coctail for us during a dive.
Well to be perfectly honest, we can alther the fraction of O2 to Diluent although it's a bit harder (but not impossible) to alter the N2/He fractions with respect to each other.

So, our hypothetical RB diver (not RB80 or ED04) has two questions.

1) Would using DIR standard gasses as bailouts allow as transition to DOTF assuming that all had gone bad and one's day was looking like it was about to be ruined.

2) Why not conduct the whole dive using DOTF procedures?
Given that the constantly changing PO2s etc. vs discrete gas mixes equate to smoothing the curve in much the same way as putting in lots of small stops and slow ascents is better than a 9m and 6m stop a la bsac, for instance.

Discuss/flame

PBrown · February 16th, 2006, 02:21 PM

I suspect you may get a better answer on some of the 'breather based forums, but my initial thoughts are that it should work, with some caveats.

1. The bottom time ppO2 would need to be fairly stable and reflect a standard gas. This would potentially be more of an issue on your choice of 'breather.

2. Depending upon the length of the dive, don't push the ppO2. My concern here would be over frying the lungs on some of the deeper stops and reducing their effectiveness, on OC we get a natural break moving up the water column.

Why not try it & let us know? :-)

btw, I don't have a Tech 1 ticket, nor will I push your wheelchair around.

cheers,
Paul

*peter_steinhoff* · February 16th, 2006, 02:54 PM

Deco on the fly isn't any magic at all. It's just an approximation of a mathematically derived decompression schedule. We then change some things which we believe will get better results, like gasbreaks, O2 window etc.

STEP 1 - How much deco?
You could do the same thing using any gas or any kind of deco algorithm. I don't have a CCR so I haven't played with constant PO2 deco. Just take your favorite decompression software and run all profiles in the time and depth range you dive in. Start with square profiles. Then look for relationships between bottomtime and total deco time. A wild guess is that the deco will probably be easier to calculate than on OC.

STEP 2 - What does the curve look like?
Then take a look at the how the stops are generated by the software - the deco curve. Usually shorter dives will spend relativly more time shallow to get a higher offgasing gradient. I suggest looking at the profiles and see if you can find some relations or just apporimate them by feel. My guess is that it will be a nice curve.

STEP 3 - Multilevel dives?
Finally you need to figure out how to calculate multilevel dives. Since the gasmix changes with depth it has to be different than OC. Use two level dives like 20 minute at 50m followed by 20 minute at 40m and see what square profile will give the same decompression. Then try the other way around, shallow to deep. You should be able to find some method to approximate your findings. Average depth will probably be to conservative.

Good luck!

Best,
Peter

EDIT. added headings for clarity

*peter_steinhoff* · February 16th, 2006, 04:40 PM

Just for the fun of it I had a look at a CCR table (IANTD VPM).
http://www.diveriteexpress.com/rebre.../img/c3103.jpg

If we take a look at 150ft/45m we will find that the deco is approx 90% of the bottom time.

The deco curve is slightly funky at 20ft (the 20ft stop is shorter than the 30ft). That is because we have a 15ft stop as the last one so we are able to leave the 20ft stop faster.

If we look at the stop times we will find that we have almost fifty-fifty relationship in stop times deeper than 20ft and 20ft and up.

The first real stops start at 80ft for BT>25min so that is about 60% of the maximum depth in ATA. I suggest we throw in some short 30 sec stops from 80% of the max depth.

So an example would be if we did a dive at this depth for 30 minutes we would do this:

1. How much deco? 90% of a 30min BT is, 3*9=27, so about 27 minutes.

2. We will do slightly less than half above 20 ft, lets make that 12 minutes. And the remaining 15 minutes at 20ft and up.

4. We have 12 minutes to spread out on 6 stops and obviously the shallower ones needs to be the longest. In average that is 2 minutes per stop. Lets try this:

80ft 1 min
70ft 1 min
60ft 1 min
50ft 2 min
40ft 3 min
30ft 4 min

5. And the shallow stops are 15 minutes. Since we don't want to do the stupid 15 ft stop lets do 1/3 at 20ft and 2/3 at 10 ft.

20ft 5 min
10ft 10min

6. So the end result is:

150ft 30 min
110ft 30 sec
100ft 30 sec
90ft 30 sec
80ft 1 min
70ft 1 min
60ft 1 min
50ft 2 min
40ft 3 min
30ft 4 min
20ft 5 min
10ft 10min

And how was that compared to the table?

The table says (runtimes converted to stoptimes):
150ft 30 min
80ft 1 min
70ft 1 min
60ft 1 min
50ft 1 min
40ft 3 min
30ft 4 min
20ft 2 min
15ft 8 min

Comparing the two schedules we were a couple of minutes more conservative at the shallow stops. But still close enough I would say.

The big question is - are we are going to see a pile of VR3s on ebay now :D :D :D

Cheers,
Peter

prharris · February 16th, 2006, 04:49 PM

Thanks Peter,
I'm at work and not run any times myself yet.
So it seems to work then, at the sub 50m level?

Just off to place an add on ebay - well not just yet

r
Paul

*peter_steinhoff* · February 16th, 2006, 04:59 PM

Quote: (Originally Posted by prharris)

Thanks Peter,
I'm at work and not run any times myself yet.
So it seems to work then, at the sub 50m level?

Just off to place an add on ebay - well not just yet

r
Paul

Paul,
I expect it would work at any depth/time but you have to make your own rules, like the one I did above. Can't use something that people have done for OC.

Cheers,
Peter

PS. This is the same process as making a set of rules for OC diving for example using another deco algorithm, conservatism setting, gas selection etc. In my own classes I don't teach people the rules so they can come up with a deco schedule on the fly. I teach them the process and the thinking behind it, so they can make up their own rules. Something I picked up from GI actually. He would never say straight out what kind of deco you should do but rather give you enough information so you could come up with the answer yourself.

prharris · February 16th, 2006, 05:25 PM

Quote: (Originally Posted by peter_steinhoff)

Paul,
I expect it would work at any depth/time but you have to make your own rules, like the one I did above. Can't use something that people have done for OC.

Cheers,
Peter

PS. This is the same process as making a set of rules for OC diving for example using another deco algorithm, conservatism setting, gas selection etc. In my own classes I don't teach people the rules so they can come up with a deco schedule on the fly. I teach them the process and the thinking behind it, so they can make up their own rules. Something I picked up from GI actually. He would never say straight out what kind of deco you should do but rather give you enough information so you could come up with the answer yourself.

Yes,
Pretty much the same as JJ deco talk at the end of our Cave ! in 2000, sat around one of the tables at Madison after our last dive

But it was a long time ago and much to my embarrasment, I'm not as up-to-date as I used to be.

r
Paul

*peter_steinhoff* · February 16th, 2006, 05:59 PM

Quote: (Originally Posted by prharris)

Yes,
Pretty much the same as JJ deco talk at the end of our Cave ! in 2000, sat around one of the tables at Madison after our last dive

But it was a long time ago and much to my embarrasment, I'm not as up-to-date as I used to be.

r
Paul

Yes, you should be really ashamed of yourself.

First taking JJs cave class and then buying a CCR...

Honestly, Jarrod is a good guy and he knows what he is talking about but hey, there is nothing to be embarrassed of here. We forget things that we don't do - it's the brain's automatic garbage disposal.

Cheers,
Peter

Mark Chase · February 16th, 2006, 07:39 PM

The long and short of it is....

Yes

I use DOTF as a last resort OH MY God deco plan and it works as good as anything else. I have run DOTF profiles designed for 50% and 100% and plotted them against bailout profiles for 32% and 80% and frankly its good enough to get you back on the boat and you can always pad it a bit here and there if you want / have the gas.

What its not good for is the fastest way out of the water. That takes a bit of planning and a table top PC.

ATB

Mark Chase

*peter_steinhoff* · February 16th, 2006, 11:11 PM

Quote: (Originally Posted by Mark Chase)

What its not good for is the fastest way out of the water. That takes a bit of planning and a table top PC.

It's not the method that sets the limit how fast you can decompress, it's your body.
Everything else is just an illusion...

Best,
Peter

February 16th, 2006, 01:24 PM	#1 (permalink)
prharris(Offline) New Member Join Date: Nov 2005 Location: Plymouth Posts: 91	Dotf Ok, I've check with an admin and it's ok to post this here It's a DOTF question. We all know AG has published his take on it so it's in the public domain, but I also appreciate the feelings of those Tech 1 peeps who were asked not to divulge what they learnt on the course. Anyway, one of the stipulations/rules/recommendations for DOTF is that you have the correct gasses, and these match with the GUE recommended gasses, fair enough! Now, some of us that have managed to sneak on here have devices that will mix a supposedly perfect coctail for us during a dive. Well to be perfectly honest, we can alther the fraction of O2 to Diluent although it's a bit harder (but not impossible) to alter the N2/He fractions with respect to each other. So, our hypothetical RB diver (not RB80 or ED04) has two questions. 1) Would using DIR standard gasses as bailouts allow as transition to DOTF assuming that all had gone bad and one's day was looking like it was about to be ruined. 2) Why not conduct the whole dive using DOTF procedures? Given that the constantly changing PO2s etc. vs discrete gas mixes equate to smoothing the curve in much the same way as putting in lots of small stops and slow ascents is better than a 9m and 6m stop a la bsac, for instance. Discuss/flame

February 16th, 2006, 02:54 PM	#3 (permalink)
peter_steinhoff(Offline) Instructor candidate Join Date: Dec 2005 Location: Sweden & Florida Posts: 205	Deco on the fly isn't any magic at all. It's just an approximation of a mathematically derived decompression schedule. We then change some things which we believe will get better results, like gasbreaks, O2 window etc. STEP 1 - How much deco? You could do the same thing using any gas or any kind of deco algorithm. I don't have a CCR so I haven't played with constant PO2 deco. Just take your favorite decompression software and run all profiles in the time and depth range you dive in. Start with square profiles. Then look for relationships between bottomtime and total deco time. A wild guess is that the deco will probably be easier to calculate than on OC. STEP 2 - What does the curve look like? Then take a look at the how the stops are generated by the software - the deco curve. Usually shorter dives will spend relativly more time shallow to get a higher offgasing gradient. I suggest looking at the profiles and see if you can find some relations or just apporimate them by feel. My guess is that it will be a nice curve. STEP 3 - Multilevel dives? Finally you need to figure out how to calculate multilevel dives. Since the gasmix changes with depth it has to be different than OC. Use two level dives like 20 minute at 50m followed by 20 minute at 40m and see what square profile will give the same decompression. Then try the other way around, shallow to deep. You should be able to find some method to approximate your findings. Average depth will probably be to conservative. Good luck! Best, Peter EDIT. added headings for clarity __________________ Peter Steinhoff GUE DIR-F, Tech1, Tech2, Cave1, Cave2, Cave3, RB80-1&2, DIR-F/Cave Instructor Candidate. NAUI Tec Instructor (Trimix, Technical DPV, Technical Wreck Penenetration etc) WKPP Support Diver, Halcyon Product Development Team, Gavinscooter Representative. Various IANTD, NSS-CDS, NACD, PADI & NAUI. ---------------------------------------------- http://dir-diver.com http://peter.steinhoff.se (swedish only) Last edited by peter_steinhoff; February 16th, 2006 at 03:30 PM.

February 16th, 2006, 04:40 PM	#4 (permalink)
peter_steinhoff(Offline) Instructor candidate Join Date: Dec 2005 Location: Sweden & Florida Posts: 205	Just for the fun of it I had a look at a CCR table (IANTD VPM). http://www.diveriteexpress.com/rebre.../img/c3103.jpg If we take a look at 150ft/45m we will find that the deco is approx 90% of the bottom time. The deco curve is slightly funky at 20ft (the 20ft stop is shorter than the 30ft). That is because we have a 15ft stop as the last one so we are able to leave the 20ft stop faster. If we look at the stop times we will find that we have almost fifty-fifty relationship in stop times deeper than 20ft and 20ft and up. The first real stops start at 80ft for BT>25min so that is about 60% of the maximum depth in ATA. I suggest we throw in some short 30 sec stops from 80% of the max depth. So an example would be if we did a dive at this depth for 30 minutes we would do this: 1. How much deco? 90% of a 30min BT is, 3*9=27, so about 27 minutes. 2. We will do slightly less than half above 20 ft, lets make that 12 minutes. And the remaining 15 minutes at 20ft and up. 4. We have 12 minutes to spread out on 6 stops and obviously the shallower ones needs to be the longest. In average that is 2 minutes per stop. Lets try this: 80ft 1 min 70ft 1 min 60ft 1 min 50ft 2 min 40ft 3 min 30ft 4 min 5. And the shallow stops are 15 minutes. Since we don't want to do the stupid 15 ft stop lets do 1/3 at 20ft and 2/3 at 10 ft. 20ft 5 min 10ft 10min 6. So the end result is: 150ft 30 min 110ft 30 sec 100ft 30 sec 90ft 30 sec 80ft 1 min 70ft 1 min 60ft 1 min 50ft 2 min 40ft 3 min 30ft 4 min 20ft 5 min 10ft 10min And how was that compared to the table? The table says (runtimes converted to stoptimes): 150ft 30 min 80ft 1 min 70ft 1 min 60ft 1 min 50ft 1 min 40ft 3 min 30ft 4 min 20ft 2 min 15ft 8 min Comparing the two schedules we were a couple of minutes more conservative at the shallow stops. But still close enough I would say. The big question is - are we are going to see a pile of VR3s on ebay now :D :D :D Cheers, Peter __________________ Peter Steinhoff GUE DIR-F, Tech1, Tech2, Cave1, Cave2, Cave3, RB80-1&2, DIR-F/Cave Instructor Candidate. NAUI Tec Instructor (Trimix, Technical DPV, Technical Wreck Penenetration etc) WKPP Support Diver, Halcyon Product Development Team, Gavinscooter Representative. Various IANTD, NSS-CDS, NACD, PADI & NAUI. ---------------------------------------------- http://dir-diver.com http://peter.steinhoff.se (swedish only)

February 16th, 2006, 04:59 PM	#6 (permalink)
peter_steinhoff(Offline) Instructor candidate Join Date: Dec 2005 Location: Sweden & Florida Posts: 205	Quote: (Originally Posted by prharris) Thanks Peter, I'm at work and not run any times myself yet. So it seems to work then, at the sub 50m level? Just off to place an add on ebay - well not just yet r Paul Paul, I expect it would work at any depth/time but you have to make your own rules, like the one I did above. Can't use something that people have done for OC. Cheers, Peter PS. This is the same process as making a set of rules for OC diving for example using another deco algorithm, conservatism setting, gas selection etc. In my own classes I don't teach people the rules so they can come up with a deco schedule on the fly. I teach them the process and the thinking behind it, so they can make up their own rules. Something I picked up from GI actually. He would never say straight out what kind of deco you should do but rather give you enough information so you could come up with the answer yourself. __________________ Peter Steinhoff GUE DIR-F, Tech1, Tech2, Cave1, Cave2, Cave3, RB80-1&2, DIR-F/Cave Instructor Candidate. NAUI Tec Instructor (Trimix, Technical DPV, Technical Wreck Penenetration etc) WKPP Support Diver, Halcyon Product Development Team, Gavinscooter Representative. Various IANTD, NSS-CDS, NACD, PADI & NAUI. ---------------------------------------------- http://dir-diver.com http://peter.steinhoff.se (swedish only) Last edited by peter_steinhoff; February 16th, 2006 at 05:12 PM.

February 16th, 2006, 05:59 PM	#8 (permalink)
peter_steinhoff(Offline) Instructor candidate Join Date: Dec 2005 Location: Sweden & Florida Posts: 205	Quote: (Originally Posted by prharris) Yes, Pretty much the same as JJ deco talk at the end of our Cave ! in 2000, sat around one of the tables at Madison after our last dive But it was a long time ago and much to my embarrasment, I'm not as up-to-date as I used to be. r Paul Yes, you should be really ashamed of yourself. First taking JJs cave class and then buying a CCR... Honestly, Jarrod is a good guy and he knows what he is talking about but hey, there is nothing to be embarrassed of here. We forget things that we don't do - it's the brain's automatic garbage disposal. Cheers, Peter __________________ Peter Steinhoff GUE DIR-F, Tech1, Tech2, Cave1, Cave2, Cave3, RB80-1&2, DIR-F/Cave Instructor Candidate. NAUI Tec Instructor (Trimix, Technical DPV, Technical Wreck Penenetration etc) WKPP Support Diver, Halcyon Product Development Team, Gavinscooter Representative. Various IANTD, NSS-CDS, NACD, PADI & NAUI. ---------------------------------------------- http://dir-diver.com http://peter.steinhoff.se (swedish only)

February 16th, 2006, 02:21 PM	#2 (permalink)
PBrown (Online) New Member Join Date: Nov 2005 Location: Wiltshire Posts: 198	I suspect you may get a better answer on some of the 'breather based forums, but my initial thoughts are that it should work, with some caveats. 1. The bottom time ppO2 would need to be fairly stable and reflect a standard gas. This would potentially be more of an issue on your choice of 'breather. 2. Depending upon the length of the dive, don't push the ppO2. My concern here would be over frying the lungs on some of the deeper stops and reducing their effectiveness, on OC we get a natural break moving up the water column. Why not try it & let us know? :-) btw, I don't have a Tech 1 ticket, nor will I push your wheelchair around. cheers, Paul

February 16th, 2006, 04:49 PM	#5 (permalink)
prharris(Offline) New Member Join Date: Nov 2005 Location: Plymouth Posts: 91	Thanks Peter, I'm at work and not run any times myself yet. So it seems to work then, at the sub 50m level? Just off to place an add on ebay - well not just yet r Paul

February 16th, 2006, 05:25 PM	#7 (permalink)
prharris(Offline) New Member Join Date: Nov 2005 Location: Plymouth Posts: 91	Quote: (Originally Posted by peter_steinhoff) Paul, I expect it would work at any depth/time but you have to make your own rules, like the one I did above. Can't use something that people have done for OC. Cheers, Peter PS. This is the same process as making a set of rules for OC diving for example using another deco algorithm, conservatism setting, gas selection etc. In my own classes I don't teach people the rules so they can come up with a deco schedule on the fly. I teach them the process and the thinking behind it, so they can make up their own rules. Something I picked up from GI actually. He would never say straight out what kind of deco you should do but rather give you enough information so you could come up with the answer yourself. Yes, Pretty much the same as JJ deco talk at the end of our Cave ! in 2000, sat around one of the tables at Madison after our last dive But it was a long time ago and much to my embarrasment, I'm not as up-to-date as I used to be. r Paul

February 16th, 2006, 07:39 PM	#9 (permalink)
Mark Chase(Offline) New Member Join Date: Nov 2005 Location: Kent England Posts: 905	The long and short of it is.... Yes I use DOTF as a last resort OH MY God deco plan and it works as good as anything else. I have run DOTF profiles designed for 50% and 100% and plotted them against bailout profiles for 32% and 80% and frankly its good enough to get you back on the boat and you can always pad it a bit here and there if you want / have the gas. What its not good for is the fastest way out of the water. That takes a bit of planning and a table top PC. ATB Mark Chase __________________ The only DIR Inspiration diver in the village

February 16th, 2006, 11:11 PM	#10 (permalink)
peter_steinhoff(Offline) Instructor candidate Join Date: Dec 2005 Location: Sweden & Florida Posts: 205	Quote: (Originally Posted by Mark Chase) What its not good for is the fastest way out of the water. That takes a bit of planning and a table top PC. It's not the method that sets the limit how fast you can decompress, it's your body. Everything else is just an illusion... Best, Peter __________________ Peter Steinhoff GUE DIR-F, Tech1, Tech2, Cave1, Cave2, Cave3, RB80-1&2, DIR-F/Cave Instructor Candidate. NAUI Tec Instructor (Trimix, Technical DPV, Technical Wreck Penenetration etc) WKPP Support Diver, Halcyon Product Development Team, Gavinscooter Representative. Various IANTD, NSS-CDS, NACD, PADI & NAUI. ---------------------------------------------- http://dir-diver.com http://peter.steinhoff.se (swedish only)