Skipping surface intervals - DIR or not?

[jonnythan]

GUE classes aren't ever going to be consistent in content over time because they evolve as DIR evolves.

Also I don't see how v-planner would help you with min deco dives, and I'm surprised they would teach that in a GUE as opposed to decoplanner.

I didn't say V-planner was DIR. You asked me what I used. V-planner isn't DIR or GUE.

Just to be clear.

 

[*Floater*]

However, you're just diving the very same house reef over and over. What's the idea of diving the same site all the time?

I was planning on skipping the surface intervals when we go to some of the further away, better sites by boat. The ride can take 3-5 hours so once we are there I'd rather do 3-4 dives rather than the regular 2 that are included. I'd pay extra of course for the tanks, second DM and other applicable expenses. But I'd rather not have a DM thumbing our dives when we still had plenty of time left.

 

[jonnythan]

Out of curiosity, can you give me an example of a moderately "aggressive" pair of profiles you would do without a surface interval?

 

[*Floater*]

Out of curiosity, can you give me an example of a moderately "aggressive" pair of profiles you would do without a surface interval?

First dive (on ean32):
100' 30 min (including a quick descent)
70' 31.5 min (ascent + 30 sec stop at 70')
0' 38 min with a 30 sec ascent followed by 30 sec stop each 10 ft

On the surface I would replace the tanks and do whatever else I needed to do (change batteries, go over dive plan, etc.)

Then I'd repeat the first dive profile. Since I'm still new to the system I would add an extra minute to the last 3 stops just to be a little more conservative and to see how I'd feel afterwards.

edit: i simplied the profile a little to remove the pauses. same total time though.

 

[dbulmer]

<deleted>

 

[Diver0001]

First dive (on ean32):
100' 30 min (including a quick descent)
70' 31.5 min (ascent + 30 sec stop at 70')
0' 38 min with a 30 sec ascent followed by 30 sec stop each 10 ft

On the surface I would replace the tanks and do whatever else I needed to do (change batteries, go over dive plan, etc.)

Then I'd repeat the first dive profile. Since I'm still new to the system I would add an extra minute to the last 3 stops just to be a little more conservative and to see how I'd feel afterwards.

edit: i simplied the profile a little to remove the pauses. same total time though.

Floater,

Let's just step back a minute and not look at the details.

What context gave rise to ratio deco the way you were taught it? Was it a context involving aggressive multi-day repetative diving? Most (if not all) models break down in this context. What makes you so sure that *this* model, which was neither developed for, nor tested in this context will hold up?

In a similar line, what does your intuition tell you is the maximum run-time of a chain of dives without surface intervals before you *must* make a surface interval to off-gas slow tissues? How long do you think that surface interval needs to be?

My gut feeling (having NOT tested this) is that you could probably make 5 hours of runtime without stopping but you'd probably need a 30 hour SI after that. How did I get these numbers? If you don't like these numbers, how would you come to a number you're comfortable with.....?

In either case, before you try to apply the technique for a long series of dives I would be highly recommend running the scenarios through decompression software. A few dives, a couple hours of runtime in a row in one day, I believe that. But none of the models are particularly adept at planning for a long series of repetative shallow dives, which is what ratio deco will eventually give you in terms of effect.

Somethign for you to consider.

R..

 

[*Floater*]

Air diving is not DIR, and I can assure you that GUE will not be publishing any air tables. Whatever air tables you were given were neither GUE nor DIR.

So much for GUE classes being consistent in quality and content across the board.

Oh well.

Just so no no one gets the wrong idea. Martin thaught me the rules that generate the tables more than the tables themselves (and filled in the shallow values upon request), and I think that's what GUE instructors teach these days. Also I guess the air table becomes the 21/35 table once helium is introduced. And Martin doesn't advocate air diving, to the contrary he calls it dangerous and unhealthy. I don't even think he even dives nitrox below 24m.

 

[Jai Bar]

I don't really know how GUE teach tables and SI's. However, it does not sound a good idea to skip SI.

When we increase the ambient pressure (e.g. "dive"), Nitrogen is absorbed into the various tissues, according to some basic physical laws. When we decrease the pressure (e.g. "ascend"), this dissolved N2 goes out of the tissues, into the blood system and- hopefully- to the lungs and exhaled to the open seas (at least in an Open circuit ).

This process of ongassing/offgassing depends on the pressure *difference*. If you dive deeper, the N2 partial pressure (PPN2) difference between tissues and blood is higher --> more N2 goes from blood to tissue.

When ascending, the PPN2 difference is negative (we go from high PPN2 to lower PPN2)- the bigger the difference the faster rate of offgassing. Therefor, If you want to achieve faster offgassing you'd like to increase the PPN2 difference --> it will *allways* be- no matter what type of dive profile- at the surface.

Actually, it is so true, that one will have even better offgassing when going to higher altitude instead of staying at sea level. Alas, ascending too fast (or decreasing PPN2 by climbing up) may cause a "too good" offgasing which most divers prefer to avoid in order not to get "bent".

Since this phenomenon was discovered, many works and models were tested in order to achieve the best ascent rate and PPN2 differences that can get a diver out of the water as fast as possible- but avoiding DCS risks, taking into consideration the dive profile and N2 loads from previous dives. Dive tables do that, computers do that, software do that too.

Physical models that try to describe N2 loading in tissues have been modified, newer ones introduced but the basics are just the same: want to get rid of N2? --> decrease the PPN2 as much as posssible by the limitations of the model/table/computer. There is no magic- it is allways best to surface, and you'll never find a combination of black magic deep stops or whatever you call them- that will allow repetive dives with shorter SI (compared to spending the same amount of time at the surface instead).

What you are suggesting is merely an extended multi-level dive (take any series of dives, decrease the SI to zero and you have "joined" two dives into a londer one). Now it really depends on which profiles you are intending to do in order to make it a safe dive.
I really don't see how one can trace the amount of N2 dissolved in tissue "on the flight", without dive tables/computer/software, deduce SI, repetitive dive profiles etc. It is not something one can easily do with an abacus. But maybe a take a GUE course and learn something new...

 

[mania]

I have splitted the orignal thread - Floater I hope you don't mind.
The part that was about diving DIR in Egypt still stays in the Red Sea forum while here I moved part about surface intervals and algorithms.
Regards to you all
Mania

 

[Charlie99]

Perhaps GUE will put something in writing when they, hopefully, put out written material for their soon-to-be-released OW course. Unless the GUE OW course instructions on deco and tables is "take a course. (PADI, NAUI, YMCA, SSI, take your choice)"

Whether or not the various posts on what are supposedly the GUE teaching in DIR-F are accurate, the lack of written material obviously leads to misunderstanding by students.

It doesn't sound very DIR to me.

Charlie Allen