Altitude

Replies to This Discussion

Permalink Reply by Andrew Georgitsis on September 4, 2009 at 9:56am

Shawn

Great question as a lot of people are curious. The answer is no, it is built into Ratio Deco Strategy. In other words we do our deco underwater not on the surface.


AG

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Permalink Reply by Michael Soldwisch on September 4, 2009 at 10:29am

You may want to check out some of the contact us section on the http://www.nmde.org website. The NMDE group does a lot of altitude diving and many be able to provide some insights.

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Permalink Reply by Shawn Bullock on September 15, 2009 at 8:45pm

Thanks AG. Do we still need to wait 12 - 24 hours balancing our nitrogen obsorption when arriving at an altitude destination? It'll take a while to get used to the idea that we needn't any adjustments at altitude.

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Permalink Reply by Scott Ekkelboom on September 17, 2009 at 10:06am

Though I can't speak for AG or the group here at UTD, we normally do not wait for any balancing when diving at altitude. It's normal for us to drive up to Tahoe, get in the water within an hour of arriving, do a dive anywhere in the 100'-250' range, and turn around and drive home the same day. This normally occurs with a 12 hour window. Again, our decompression is done in the water via Ratio Deco and solid decompression strategies and not on the surface after the dive.

Shawn Bullock said:

Thanks AG. Do we still need to wait 12 - 24 hours balancing our nitrogen obsorption when arriving at an altitude destination? It'll take a while to get used to the idea that we needn't any adjustments at altitude.

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Permalink Reply by Shawn Bullock on September 18, 2009 at 8:51pm

Understood. Thanks. This really does make the tables easy to use and understand.

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Permalink Reply by George K. Watson on September 30, 2009 at 8:14am

Coming from the highest state in the union, I can say that we make no adjustments when diving here. Our lowest diving/training altitude is at 5200'/1600m and the highest we regularly dive is at 10,600'/3200m, quite a bit more altitude than most. The biggest adjustment we make is to make sure that all sealed equipment (scooter, camera bodies, light canisters) is unsealed before making an altitude transition.

I may get a chance to dive some 12,000'/3700m glacial tarns next year, and don't expect to have to adjust anything other than my drysuit underwear.

Since I live at 8300'/2500m I have been curious about the effect of the physiological differences I have and their effect on diving. I have not found anyone even speculating on this.

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Permalink Reply by Scott Ekkelboom on September 30, 2009 at 8:29am

George K. Watson said:

Coming from the highest state in the union, .

\
Between the Govenator, Humbolt County and legalized Marijuana...I thought California was the highest state in the union. ;)

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Permalink Reply by Justin Daniels on December 1, 2009 at 4:17pm

I have not been through the Ratio Deco class, but can you elaborate on this a little bit?
We are not talking about surface stuff here.
If I am diving at 8000 feet, how would Ratio Deco factor in the additional theoretical depth at altitude?

Andrew Georgitsis said:

Shawn

Great question as a lot of people are curious. The answer is no, it is built into Ratio Deco Strategy. In other words we do our deco underwater not on the surface.


AG

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Permalink Reply by Matthew Ross on December 14, 2009 at 6:14pm

Am I to take this to mean that the tissue loading (of N2, say) at the end of Ratio Deco should be less than ambient at the surface regardless of what the ambient surface partial pressure is?

Andrew Georgitsis said:

Shawn

Great question as a lot of people are curious. The answer is no, it is built into Ratio Deco Strategy. In other words we do our deco underwater not on the surface.


AG

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Permalink Reply by Mark Chase on December 28, 2009 at 9:56am

Justin Daniels said:

I have not been through the Ratio Deco class, but can you elaborate on this a little bit?
We are not talking about surface stuff here.
If I am diving at 8000 feet, how would Ratio Deco factor in the additional theoretical depth at altitude?

Andrew Georgitsis said:

Shawn

Great question as a lot of people are curious. The answer is no, it is built into Ratio Deco Strategy. In other words we do our deco underwater not on the surface.


AG

Unless there’s some new magic I am unaware of Ratio deco is and always has been a ball park approximation of actual decompression tables and it needs experimentation and comparison in order to be useful.

QED it is not a decompression theory in its own right it is merely a simple mathematical progression that approximates a decompression theory.

I use ratio deco but my base line for trimix deco is Buhl man Decompression running a 10/90GF

I work the ratio around the diving I do and I compare the results with my base line of Buhlman on 10/90GF. Then I adjust my RD results to match 10/90 as close as I can in a +/- 10m depth range.

If I ran VPMB I am sure my ratio deco would be different. If I ran 20/80GF? I know it would be different.

QED it’s not a deco system. What it is to me is a model that saves me a lot of money on buying a decent back up wet deco computer. What it is to some people is a model that saves them spending money on a wet deco system but doesn’t avoid the need for a dry comparison model like Decoplanner or V Planner.


SO in answer to the altitude question? The ratio deco will work perfectly for the model you will develop using comparison with a proper decompression package and how you feel post dive.



ATB

Mark

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Permalink Reply by Andrew Georgitsis on December 31, 2009 at 9:11am

Mark

I very much appreciate your answer, but want to be sure that you understand that your approach is different to my approach. Both the Bulhman and VPM models, I feel, are incorrect ESPECIALLY when doing longer bottom times, they really expose how incorrect they are. They also give you incorrect shape. In other words if I was to compare the dives we did recently in Mexico, in a cave called "The Pit" to a Bulhman or VPM model using your settings, it would of given me a 1200 + minute of deco or 850+ minute of deco, respectively. (Our bottom time was 150 mins at an average of 300'/90m with a max of 350'/110m using 10/70) In reality we ran a "Max Deco" profile which is essentially a 400 mins of deco profile. That is a 1/3 of Bulhman's profile and not only that very different in shape.

Where my approach differs to your is I know Max Deco works and know it shape and stop times. So I looked at these times and and then I related (Ratio) them back to shorter bottom times and depths. I then developed a strategy for bottom time to a deco time in the O2 segment. Once I knew that I was able to figure the rest of deco out and shape based on that. After that I came up with Ratio Deco which is essentially a beginners type approach of using set points of 1:1 and so on to get divers started and weened off their computers with Bulhamn models built in. These 1:1 and 1:2 rules are for beginners in technical and trimix diving that would get them to eventually get to the "proper" ratio deco of relating BT to O2 time. Then, I tweeked the "Workman" style schedules (Decoplanner 30/90) or (VPM) to match these overall times , still not shape, but at least times to give divers the warm fuzzy that you are within "Norm."

In reality, Bulhman theory is so bad that if you were to run Bulhman you would bend yourself every dive, which is why you need to throw the 10/90 in there to get it to give you some reasonable ascent profile, even though the shape is messed up, you can still tweak it out to meet a proper ascent profile. But hey, It does gives a diver the warm fuzz about deco planning because it comes out of a computer.....

Andrew

Mark Chase said:

Justin Daniels said:

I have not been through the Ratio Deco class, but can you elaborate on this a little bit?
We are not talking about surface stuff here.
If I am diving at 8000 feet, how would Ratio Deco factor in the additional theoretical depth at altitude?

Andrew Georgitsis said:

Shawn

Great question as a lot of people are curious. The answer is no, it is built into Ratio Deco Strategy. In other words we do our deco underwater not on the surface.


AG

Unless there’s some new magic I am unaware of Ratio deco is and always has been a ball park approximation of actual decompression tables and it needs experimentation and comparison in order to be useful.

QED it is not a decompression theory in its own right it is merely a simple mathematical progression that approximates a decompression theory.

I use ratio deco but my base line for trimix deco is Buhl man Decompression running a 10/90GF

I work the ratio around the diving I do and I compare the results with my base line of Buhlman on 10/90GF. Then I adjust my RD results to match 10/90 as close as I can in a +/- 10m depth range.

If I ran VPMB I am sure my ratio deco would be different. If I ran 20/80GF? I know it would be different.

QED it’s not a deco system. What it is to me is a model that saves me a lot of money on buying a decent back up wet deco computer. What it is to some people is a model that saves them spending money on a wet deco system but doesn’t avoid the need for a dry comparison model like Decoplanner or V Planner.


SO in answer to the altitude question? The ratio deco will work perfectly for the model you will develop using comparison with a proper decompression package and how you feel post dive.



ATB

Mark

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Permalink Reply by Mark Chase on December 31, 2009 at 9:04pm

I am familiar with the max deco profile (or at least GI3's one) but I had thought that was something thrashed out with Hamilton rather than any form of actual ratio deco? Also, with a spell on 02 at 30' id assume it was habitat only?

In the GUE tec manual they still use 30/90 as a guide for the intermediate stops and obviously encourage the 80% ata deep stop with the modified ascent rates to manage the deeper stops. But the key thing for me in the Tec manual is the focus of comparison with either VPM or Gradient factor base lines until you develop your own comfort zone using RD.

By virtue of the fact my personal bit of ocean is 50-80m deep all over (English Channel from Dover round to Littlehampton); I do 90% of my diving in that depth range. I dive GFs using a Shearwater wet computer but I run ratio deco on every dive as a back up plan. As a result I have a lot of comparison data with GUE stile RD profiles in this range.

The things that become obvious are that RD on a 50-55m dive (1:1 ratio) is very conservative. The deco is much longer than I would do running 10/90 and the deep stops are much deeper. However in the 60-65m range, RD running 2:1 becomes very aggressive in comparison to 10/90 particularly in the 65m dives where it equates more like 10/120GF

I have done dives with 100+gfs and walked away just fine, but I have also driven on the motorway at 100+ with no problems, but that doesn’t make it safe.

For me, the tides usually limit my bottom time to 60min's max. On deeper dives my bailout gas limits me to 45mins max. So a 45min at 75m is a long exposure dive resulting in about 3.5hours in water time on 10/90GF.

With such short in water times, there is no need to push it on deco. For me once the in water time hits 4 hours +, Id look at more aggressive deco for reasons of exposure and scrubber duration.

Without going into great detail, here are two simple ways I adjust my deco using RD. On a 50m dive id ignore decent time and calculate run time from the bottom of the shot onwards. I ere on the side of shallow with my average depth calculation and Id do the last stop at 3m (weather permitting) and having cleared the stops id do a 3min ascent or less.

On a 65m dive I include decent time in run time, I ere on the side of deep with my avg depth and I clear at 6m and do a 6min ascent or more.

Simple things that don’t alter the math but do get the end result more aligned to my chosen deco.

Don’t get me wrong I am a massive fan of Ratio Deco. I hated the restrictions imposed on my by tables so I used to dive two VR3s. Now I see no need for a expensive back up computer. I am perfectly happy with the built in deco on my Shearwater display (MCCR KISS and now on my JJ) and to use RD in support. If my computer packed up id happily do any dive in the 50-80m range and run RD.

I also cross check what my computer is telling me with my RD calculations in order to ensure its not giving me garbage info.

I have no illusions as to the accuracy / or not of wet computers. I also have no illusions to my ability too do math under water :D I check the computer and the computer checks me.

So far there has only been one occasion where I found the computer at fault (depth sensor error) usually if there is a serious discrepancy? It’s my math that’s out.

ATB

Mark

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