Altitude

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Permalink Reply by Mark Chase on January 1, 2010 at 3:18am

For the sake of discussion, hear is a piece I wrote a few years ago on a comparison of RD on a shallow dive and a 65m dive. I was running 10/85 deco in those days as this was a one of the fixed set of options on my Hammer Head computer.

Clare Gledhill is a friend and a GUE instructor. After she and Bob did a dive on a well known site (The Pangarni) I was shocked by her profile. I had dived this wreck before and I knew the run time id do. This kicked off the discussion on RD and how it’s manipulated by each individual to suit their own wants. To me this wasn't accepted RD at all, it was just very aggressive deco

It’s important to note that since I wrote this GUE have changed their stance on the deep stops. There was some research carried out and it was decided the to reduce the deep stop phase by accelerating the ascent rate to 6m/min between 80% ATA and 65% ATA At 65% ascent rate was halved to 3m/min or stops doubled which ever was the greater.


If this is not suitable discussion for a UTD forum please feel free to delete it. Its winter and I have little chance of diving right now so a discussion with AG on the finer points of RD would be great but if it upsets the UTD teem I have no problem with you deleting it.

ATB

Mark


______________________________________________

1:1 ratio depth is 45m

ie 30mins at 45m = 30mins of deco from 21m and up.

However you should then take into consideration deep stops at 80% of ATA and a 1m/min ascent from 6m and an extended gas switch.

So in fact 30mins at 45m using 50% for deco will be something like

1 @ 36
1 @ 33
1 @ 31
1 @ 27
1 @ 24

+ 30mins of deco + 5min ascent from 6m to the surface.

So assuming + 1 min to get to 36m a total deco of 41mins

Running GF deco of 10/85 I would be doing 36mins of deco so ratio deco is more conservative. Then for reasons I can not fathom the DIR boys start manipulating the numbers and cutting corners and suddenly they have RD figures much shorter than this.

Lets look at Gledders example of the Pangarni:

30mins at 66m avg

Fortunately 66m is the set point depth for the 2:1 ratio. If were 3m deeper you add 5min if it were 3m shallower you take away 5min.

So it’s bang on standard for this depth 2:1 ratio

30min bottom time is 60mins deco using 50% and 100% and 15/55 back gas

You then split the deco 50% on 02 and 50% from 21m and up

So now we have a profile from 21m to 6m

Allow 5min for 02 window at 21m then pick your preferred curve to the 6m stop. F sequence S curve. I would use the S curve.

s-Curves Take the time for the segment 21m -9m and divided it by the number of stops. Seeing as they stop every 3m this will be 5.

30min divided by 5 = 6 so the shallow stop will be 6mins

So now it looks like this

6 @ 21
6 @ 18
6 @ 15
6 @ 12
6 @ 9
30 @ 6

However to get a better shape to the deco and take advantage of the 21m 50% PP02 they take half the value of the 12 and 15m stops and push it on to the 18 and 21m stop

So now we have

9 @ 21
9 @ 18
3 @ 15
3 @ 12
6 @ 9
30 @ 6

So now for the deep stops.

on a 2:1 ratio the 36m -24m zone should be 1/2 the 50% bottle time. In this case 30mins so its 15mins of deco from 36m to 21m

so now we have 36m to 21m = 5 stops I generally take half of the stop time at the shallow stop then halve it again for the next stop and so on rounding it up so it now would be

1 @ 36
1 @ 33
2 @ 30
4 @ 27
8 @ 24
9 @ 21
9 @ 18
3 @ 15
3 @ 12
6 @ 9
30 @ 6

RD has a deep stop at 80% of ATAs

I don’t know a quick way of working out ATA’s so I work on ¾ 75% of max depth which in this case is 50m

So you would pause at 50m and do a 3m/min ascent to 36m. This roughly equates to 1min stop every 3m and then you round it to fit with the 3m stops.

So our final decompression profile looks like this


1 @ 51
1 @ 48
1 @ 45
1 @ 42
1 @ 39
1 @ 36
1 @ 33
2 @ 30
4 @ 27
8 @ 24
9 @ 21
9 @ 18
3 @ 15
3 @ 12
6 @ 9
30 @ 6

Assuming a 10m/min ascent to 51m =1.5min and assuming a 5min ascent from 6m to the surface the total deco on this dive is 88mins. Bottom time 30mins total run time

118mins.

And yet Gledders did the dive in 90mins some 28mis less deco????

How this fits in with ratio deco I have no idea.

I would do the dive on a 20/85 GF My Time to Surface would be 107Mins, Total run time 137min and it would look like this

1 @ 33
3 @ 30
3 @ 27
6 @ 24
3 @ 21
4 @ 18
5 @ 15
9 @ 12
12 @ 9
42 @ 6

SO doing it DOTF (as I understand it) 118mins
Doing it Decoplaner 10/85 GF 137mins
Doing it Gledders 90mins

To get down to DOTF deco I would have to run an aggressive GF10/120

To get down to Gledders time I don’t know my computer will not accept the numbers.

ATB

Mark Chase

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Permalink Reply by Andrew Georgitsis on January 1, 2010 at 12:05pm

Mark

You and others are always welcome to post, discuss and question me or any of our methods right here on this forum or board. I welcome good healthy discussions because ultimately that is how we all learn from one another. So please never feel that we would delete your question, argument or post.

On that note, I am not sure of what GUE's "New" stance is or is not. That is of no concern to me. What is of concern, is how often people miss the finer point of Ratio Deco. Decompression is not a science, by any means, and one should not treat it as such. Decompression should be a "strategy" that one uses towards integrating all their personal and team components into the dive. This strategy should FIRST start with weighing the "Risk vs Benefits" and take into account all the components of the dive, including the team, gas selection, environment, support, safety and so on. One should also know and weigh in all of their personal attributes and consider them towards that strategy. Only then can you develop a sound approach towards your deco. No two dives will you treat the same. Once you understand this, that is when Ratio Deco becomes a powerful tool, and things like the original question in the forum "How do we consider Altitude" become moot or comparing RD to computer generated profiles become obsolete. ,

So, in your discussion below, I don't know why or how or what Clare and Bob did or did not do. Often my perception of a 65m dive for 30 mins is different.

What I do know is that in UTD, we like to train people (start them out) with a very conservative and low risk approach to RD. I want divers to focus and developing their skills and awareness, prior to really pushing around and developing their deco strategy, which to me is a basic and fundamental step. So, 1:1 at 150'/45m and 1:2 at 200'/60m is a very nice and conservative approach.

In your 1:1 example the deco for me would be

33m 1
30m 1
27m 1
24m 1
21m 4
18m 4
15m 2
12m 2
9m 3
6m 10
and then 5 up

Total would be 35mins or so. I am not sure where you got the 30 of deco and then 5 up. We include the 5 up in the 30 mins of deco.

The later example of 66m for 30 mins would be 70 mins deco (from 21m-0m) because you are 20'/6m deeper than the set point of 1:2 at 200'/60m and my run time would be 125 mins, give or take.

I could do it with a 90 mins run time (60 min ascent profile), but I know the risk is much higher than the risk of a 125 min ascent profile. So, I would weigh that against the dive, hence Risk vs Benefit and then decide.

For example, if I were making that same dive in Ras Mohammed Park, off the wall, well then I would do a full 125 min profile as the entire bottom and deco are a "Dive". However if I were making the dive on the Graf Zeppelin in the 2C degree Baltic water, I might want to do the deco in 60 mins as it is much warmer on comfortable on the Boat than floating in deco :).

So ulitametaly RD is Risk vs Benefit.

Anyways Happy New Year, I am certainly enjoying our discussions.

AG




Mark Chase said:

For the sake of discussion, hear is a piece I wrote a few years ago on a comparison of RD on a shallow dive and a 65m dive. I was running 10/85 deco in those days as this was a one of the fixed set of options on my Hammer Head computer.

Clare Gledhill is a friend and a GUE instructor. After she and Bob did a dive on a well known site (The Pangarni) I was shocked by her profile. I had dived this wreck before and I knew the run time id do. This kicked off the discussion on RD and how it’s manipulated by each individual to suit their own wants. To me this wasn't accepted RD at all, it was just very aggressive deco

It’s important to note that since I wrote this GUE have changed their stance on the deep stops. There was some research carried out and it was decided the to reduce the deep stop phase by accelerating the ascent rate to 6m/min between 80% ATA and 65% ATA At 65% ascent rate was halved to 3m/min or stops doubled which ever was the greater.


If this is not suitable discussion for a UTD forum please feel free to delete it. Its winter and I have little chance of diving right now so a discussion with AG on the finer points of RD would be great but if it upsets the UTD teem I have no problem with you deleting it.

ATB

Mark


______________________________________________

1:1 ratio depth is 45m

ie 30mins at 45m = 30mins of deco from 21m and up.

However you should then take into consideration deep stops at 80% of ATA and a 1m/min ascent from 6m and an extended gas switch.

So in fact 30mins at 45m using 50% for deco will be something like

1 @ 36
1 @ 33
1 @ 31
1 @ 27
1 @ 24

+ 30mins of deco + 5min ascent from 6m to the surface.

So assuming + 1 min to get to 36m a total deco of 41mins

Running GF deco of 10/85 I would be doing 36mins of deco so ratio deco is more conservative. Then for reasons I can not fathom the DIR boys start manipulating the numbers and cutting corners and suddenly they have RD figures much shorter than this.

Lets look at Gledders example of the Pangarni:

30mins at 66m avg

Fortunately 66m is the set point depth for the 2:1 ratio. If were 3m deeper you add 5min if it were 3m shallower you take away 5min.

So it’s bang on standard for this depth 2:1 ratio

30min bottom time is 60mins deco using 50% and 100% and 15/55 back gas

You then split the deco 50% on 02 and 50% from 21m and up

So now we have a profile from 21m to 6m

Allow 5min for 02 window at 21m then pick your preferred curve to the 6m stop. F sequence S curve. I would use the S curve.

s-Curves Take the time for the segment 21m -9m and divided it by the number of stops. Seeing as they stop every 3m this will be 5.

30min divided by 5 = 6 so the shallow stop will be 6mins

So now it looks like this

6 @ 21
6 @ 18
6 @ 15
6 @ 12
6 @ 9
30 @ 6

However to get a better shape to the deco and take advantage of the 21m 50% PP02 they take half the value of the 12 and 15m stops and push it on to the 18 and 21m stop

So now we have

9 @ 21
9 @ 18
3 @ 15
3 @ 12
6 @ 9
30 @ 6

So now for the deep stops.

on a 2:1 ratio the 36m -24m zone should be 1/2 the 50% bottle time. In this case 30mins so its 15mins of deco from 36m to 21m

so now we have 36m to 21m = 5 stops I generally take half of the stop time at the shallow stop then halve it again for the next stop and so on rounding it up so it now would be

1 @ 36
1 @ 33
2 @ 30
4 @ 27
8 @ 24
9 @ 21
9 @ 18
3 @ 15
3 @ 12
6 @ 9
30 @ 6

RD has a deep stop at 80% of ATAs

I don’t know a quick way of working out ATA’s so I work on ¾ 75% of max depth which in this case is 50m

So you would pause at 50m and do a 3m/min ascent to 36m. This roughly equates to 1min stop every 3m and then you round it to fit with the 3m stops.

So our final decompression profile looks like this


1 @ 51
1 @ 48
1 @ 45
1 @ 42
1 @ 39
1 @ 36
1 @ 33
2 @ 30
4 @ 27
8 @ 24
9 @ 21
9 @ 18
3 @ 15
3 @ 12
6 @ 9
30 @ 6

Assuming a 10m/min ascent to 51m =1.5min and assuming a 5min ascent from 6m to the surface the total deco on this dive is 88mins. Bottom time 30mins total run time

118mins.

And yet Gledders did the dive in 90mins some 28mis less deco????

How this fits in with ratio deco I have no idea.

I would do the dive on a 20/85 GF My Time to Surface would be 107Mins, Total run time 137min and it would look like this

1 @ 33
3 @ 30
3 @ 27
6 @ 24
3 @ 21
4 @ 18
5 @ 15
9 @ 12
12 @ 9
42 @ 6

SO doing it DOTF (as I understand it) 118mins
Doing it Decoplaner 10/85 GF 137mins
Doing it Gledders 90mins

To get down to DOTF deco I would have to run an aggressive GF10/120

To get down to Gledders time I don’t know my computer will not accept the numbers.

ATB

Mark Chase

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Permalink Reply by Mark Chase on January 3, 2010 at 12:10pm

That’s interesting

I have always worked on 150' (45m) 220' (66m) and 270' (81m) as set my points

With regard to the 45m dive again I have always done a 1m/min ascent from 6m. One of the restrictions / limitations of running a computer was it would get upset if you went past its deco ceiling. We had to clear the computers at 3 or 6m and then ascend.

Getting back to the point of the original poster, we both appear to be in agreement that RD needs some form of baseline for development of the divers personal interpretation of Ratio Deco. Dives can either be planned dry and compared with existing profiles or they can be compared wet, as I do, but there must be some sort of base line.

When I was taught deco it was black and white. You chose your table and dived it to the letter. When GAP Proplanner and Decoplanner became common we were given the option to accelerate or decelerate our deco. Normally the software had a recommended base line. 30/90 with Decoplanner and Level 2 with V planner are the two that spring to mind.

From this base line we started to adjust our deco to suit our own personal voodoo

The big influences for me were WKPP and Pyle who led me to believe deep stops were good and that you can greatly reduce the shallow stops on rich helium mixes.


Having adopted 10/90 as my deco of choice for GFs I then developed my methodology for ratio deco to get close to my tried and trusted 10/90 GF.


And that was really my point with the first question. Ratio deco is not a fixed line in the sand. There is no reason why RD can not be adapted to any diving preference or scenario. But it does take time to develop it. It is not an instant fix.


ATB

Mark

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