120/20 rule or a 130 rule?

[limeyx]

Au contraire, I use the example of series of 100' 30 minute repetitive dives, 11 minute ascent, 20 minute SI as merely a specific example of the philosophy that "residual nitrogen doesn't matter if you do a slow ascent"


There is a big difference between your profile and one that does just 1 minute at 30/20/10' for the first two dives, and 1 minute at 40/30/20/10' for 3rd and 4th dives, all after just a 20 minute SI. In addition, the ideal ascent profile was described as slowing to 10fpm at 80%ata. To my understanding, with EAN32/68% inert gas, even a saturated compartment/tissue would be at less pressure than ambient at 80%ata, so starting deep stops there would be counterproductive. Again, the 5th-dx sort of profile you describe, with deep stops starting aaround 50% depth makes a lot of since to me, but the 80% ata profile being taught in some GUE DIR-F classes seems a bit out of whack.

I think there is a misunderstanding on the 80% situation (or potentially 2 things being taught). We learned in DIR-F that at 80% for MDL diving, you "pause" -- this is NOT a 30sec pause 30 sec move but merely, slow down, OK the team and move.

This is more to get into "practice" with what you learn later in tech1.

We also learned stops (1 min including travel time) from 1/2 depth.

Some Rock Bottom calculations only take into account a stop at 30, 20, 10 feet for "emergency" contingency.

I dont know. Other classes may teach something different, but I did indeed take DIR-F with 5thd guys. I know that they believe what they cover in DIR-F is very conservative until the "full details" are released in later classes.

I've never really even thought about trying to minimize the SI -- it's just not very practical for the kind of diving we do here. Almost without exception every SI in my logbook is 60mins+. Some at 45-50 but unless it is two 30 foot dives, nothing really less than that.

Maybe it's possible to do 20 min SI's for as many dives as you want, but I haven't been let in on that part of things yet if so.

 

[*Floater*]

There is a big difference between your profile and one that does just 1 minute at 30/20/10' for the first two dives, and 1 minute at 40/30/20/10' for 3rd and 4th dives, all after just a 20 minute SI. In addition, the ideal ascent profile was described as slowing to 10fpm at 80%ata. To my understanding, with EAN32/68% inert gas, even a saturated compartment/tissue would be at less pressure than ambient at 80%ata, so starting deep stops there would be counterproductive. Again, the 5th-dx sort of profile you describe, with deep stops starting aaround 50% depth makes a lot of since to me, but the 80% ata profile being taught in some GUE DIR-F classes seems a bit out of whack.

Here's a quote from the 5thD-X min deco rules I've seen (empahsis mine):

"80% of your ata's (75% of your depth) begin pauses. A pause = check the team and then continue moving. Basically you're slowing your ascent rate from 30' per minute to 20-10 feet per minute. Continue every 10' until you reach 65% of your ATA's (50% of your depth).

65% of your ATA's (50% of your depth) begin 1 minute stops. A 1 minute stop includes the travel time, so it could be 30 second stop, and 30 second move. Continue all the way to the surface."

So I was taught 10'/min from 80% ATA instead of the 5thD-X's 10-20 ft/min from 80% to 65% ATA and only then up at 10'/min. That's not a big differnce IMO and I think just using 10'/min makes it simpler.

 

[rjack321]

The whole point of this is that over time, you start to get a damned good feeling of where you are relative to deco. From the combination of previous dives, hydration, sleep, gas used, current dive profile, etc. A whole lotta factors which don't go into computer algorithms. Some of these factors make your plans more conservative, some less.

I would say Jess has a very good understanding of the big picture approach. Maybe more mathematical than required, but everyone's brain works differently.

Carry on brother!

Personally, all of my SIs are longer than 90 mins, I ignore reverse profile issues, dive 32%, double shallow stops whan I can (usually there's something to see) and also ignore CNS limits (since I have never even come close to them). YMMV

 

[limeyx]

The profiles you posted, more or less 90', 31 minute, 17 minute ascent, and 80 minute SI are very reasonable profiles. Whether or not you think in these terms, your 1 hour 20 minute SI allows for offgassing of dissolved gas. It looks like you are using something similar to the 5th-dx min deco rules, which look pretty reasonable to me. If you took a dive computer along for the ride, it would be happy.

...

Well, according to some DIR-F grads, what is being taught is that, even in min deco diving, that reverse profiles are preferred. Not merely acceptable, but actually the preferred method of diving, and that forward profiles are inferior. Again, not just a minor difference in algorithm, but an entirely different philosophy.

To clarify our ascent profile. One of the divers (ironically, a recent DIR-F grad with 500+dives) asked if we could do extra time at 20 feet, and a slow ascent from there, and so we went with the most conservative. These were the two 'closest' profiles I could find easily since most of our diving here is the multi-level reef diving that everyone says you need a computer to safely dive

We dont often have recreational dives where we'd spend the whole 30 mins at max depth.

I think the concern with deepest dive first profiles is that if you do the shallower dives last, then you need to adjust your ascent profile to take into account the earlier dives (ascend slower).

if you do the deepest dive last, then the ascent will be slow enough to not induce bubbles from earlier dives.


Also, it's very important to distinguish what GUE calls a 'dive' from what the rest of us calls a dive Sometimes (e.g. in a class), they do give specific advice on a particular level of diving (DIR-F, Tech1) but a lot of GUE/WKPP public comments are for dives that 99.99% of us will likely never be trained to do.

 

[Charlie99]

So I was taught 10'/min from 80% ATA instead of the 5thD-X's 10-20 ft/min from 80% to 65% ATA and only then up at 10'/min. That's not a big differnce IMO and I think just using 10'/min makes it simpler.

They are also taught, even if not explicitly stated, that residual dissolved nitrogen IS important. That's why the 5th DX rules call for a minimum of 60 minute SI and doubling of the shallow stops. That's a lot different than your DIR-F instructor, who is happy with 20 minute SI and doing just 1-1-1-1 (or 90 second stops if one includes the move times) from 40' to 10' on the repetitive dives.

I'd dive the 5Th-DX min deco table, ascent, and rules any day and every day.

OTOH, the profiles and rules taught by your DIR-F instructor's profiles scare me.

As noted in the Computer vs No Computer thread, the profiles you and your instructor consider valid end up with 25 minutes of omitted deco (per ANDI-RGBM program at nominal) by the end of the 4th dive.

 

[limeyx]

Personally, all of my SIs are longer than 90 mins, I ignore reverse profile issues, dive 32%, double shallow stops whan I can (usually there's something to see) and also ignore CNS limits (since I have never even come close to them). YMMV

With the exception that I often dive 60 min SI's and sometimes add a 6 min ascent from 20 feet, that's essentially what I do too.

i would do 2 dives to 100 for 30 mins on 32% with 20 min SI, but any more than that scares me too much too.

 

[lamont]

They are also taught, even if not explicitly stated, that residual dissolved nitrogen IS important. That's why the 5th DX rules call for a minimum of 60 minute SI and doubling of the shallow stops. That's a lot different than your DIR-F instructor, who is happy with 20 minute SI and doing just 1-1-1-1 (or 90 second stops if one includes the move times) from 40' to 10' on the repetitive dives.

I don't think there's any officially published GUE guidelines on recreational diving and repetetive diving. I have seen an e-mail passed around with tables and guidelines to double the stops from 30 feet if doing less than (IIRC) a 2 hour SI, but I don't know exactly where that came from.

I'd dive the 5Th-DX min deco table, ascent, and rules any day and every day.

OTOH, the profiles and rules taught by your DIR-F instructor's profiles scare me.

As noted in the Computer vs No Computer thread, the profiles you and your instructor consider valid end up with 25 minutes of omitted deco (per ANDI-RGBM program at nominal) by the end of the 4th dive.

Generally all the GUE trained divers that I dive with take at least a 60 minute SI between every dive, and usually spend a lot more time doing deco. 1's from 1/2 depth followed by 3@20, 3@10 is more common, even on a first dive, and 2 fpm ascents from 30 fsw are not unheard of if there's something to look at, deco is usually governed by the person who feels like going the slowest. I don't know who taught a DIRF course where 1's from 50% of depth were acceptable even on back-to-back 30 min @ 90 fsw dives with a 20 min surface interval, and I've definitely never seen that practiced.

I, personally, don't really agree with anyone teaching 1's from 80% on a recreational dive using 32% or 30/30 since you're still ongassing at that point and you haven't begun to drive a gradient. The pause at 80% of depth also seems pretty silly to me, even from a training perspective. I do agree with doing reverse profiles, since you crush the bubbles from the first dive and then deco them out. I don't agree with ignoring repetetive recretional diving -- that is taking something that GI3 wrote about technical diving profiles and applying it to recreational diving without knowing what you're doing.

 

[*Floater*]

They are also taught, even if not explicitly stated, that residual dissolved nitrogen IS important. That's why the 5th DX rules call for a minimum of 60 minute SI and doubling of the shallow stops. That's a lot different than your DIR-F instructor, who is happy with 20 minute SI and doing just 1-1-1-1 (or 90 second stops if one includes the move times) from 40' to 10' on the repetitive dives.

I'd dive the 5Th-DX min deco table, ascent, and rules any day and every day.

OTOH, the profiles and rules taught by your DIR-F instructor's profiles scare me.

As noted in the Computer vs No Computer thread, the profiles you and your instructor consider valid end up with 25 minutes of omitted deco (per ANDI-RGBM program at nominal) by the end of the 4th dive.

The 5thD-X rules posted by Joe on the 5thD-X's DIRF forum don't mention anything about 60 minute minimum SI. But maybe he still teaches them though, I wouldn't know, or maybe AG or someone else advocates them.

Anyway, what do the 5thD-X boys and girls do if they are on a dive boat and everyone else is heading back for a second dive after only 30min SI? This by the way happened to me in Coz last month after a dive to Punta Sur which is pretty much on the NDL limits so presumably we had a bunch of residual nitrogen still in our system. I did the second dive with the others.

 

[limeyx]

The 5thD-X rules posted by Joe on the 5thD-X's DIRF forum don't mention anything about 60 minute minimum SI. But maybe he still teaches them though, I wouldn't know, or maybe AG or someone else advocates them.

Anyway, what do the 5thD-X boys and girls do if they are on a dive boat and everyone else is heading back for a second dive after only 30min SI? This by the way happened to me in Coz last month after a dive to Punta Sur which is pretty much on the NDL limits so presumably we had a bunch of residual nitrogen still in our system. I did the second dive with the others.

The 5thd-x rules as taught in our DIR-F class definitely have the 60/90 mins in them.
However, Andrew does state that these are conservative parameters, which is as it should be, since they have to make sure to teach parameters that will work for the vast majority of people (also taking into account that not every DIR-F student will make a perfect ascent etc.)

Am I saying I wouldn't jump in after a 30 min SI? I can't say that, as I've done it.
Am I saying that I would do that 4 or 5 dives in a row to 100 feet? No, as Charlie says, that's scary.

The fact that it's scary however, is based on *my* limited understanding of deco. It might not be so scary to someone used to doing 400 feet wreck dives, or hours in a cave at 300 feet.

Also, GUE definitely does NOT teach that you can ignore residual N2 on tech dives. They were very clear that after the class, it was max 2 T1 dives per day. Now, if you add extra deco to that, you can probably do more (and if I did 2 in the morning and then left 4-6 hours SI, I'd probably do 3 also). Maybe the Tech2 deco shows you that these numbers are really way too conservative, but that level of diving is a (very) long way off for me.

 

[Charlie99]

Am I saying I wouldn't jump in after a 30 min SI? I can't say that, as I've done it.

Am I saying that I would do that 4 or 5 dives in a row to 100 feet? No, as Charlie says, that's scary.

Actually, I don't have any problem with repeating the 100' 30 minute EAN32 dives with just a 20 minute or 30 minute SI. What I do have a problem with is repeating the dives with short SI and just 1-1-1-1 for the 40' and shallower stops.

It boils down to whether or not one believes that doing 10fpm or 6fpm (1 min pause 30 second 10' move) from 80% ata up to 10', and then another couple of minutes to go from 10' to surface leaves you so clean that one can ignore residual nitrogen for future dives, even after just a short SI.

Originally I thought that what was happening was that GUE instructors would talk about surfacing "clean", meaning very little free phase gas; but that what students heard was "clean", as in no residual nitrogen. Recent e-mail exchanges with a GUE instructor though, show that at least one GUE instructor is happy with the short SI, short shallow stop profile.

So far, the only divers posting that they don't buy into that philosophy have been 5th DX trained divers.

How about you other GUE-trained divers ??? Short SI + short shallow stops OK on repetitive dives?

Charlie Allen