120/20 rule or a 130 rule?

[*Floater*]

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?

I'm also curious to hear how others here who don't use computers were taught to handle short SI's when diving with computer-using buddies? Obviously you could just not dive with such buddies when they head back after not waiting for a full hour, but to me that would seem like a major limitation of your system.

 

[limeyx]

I'm also curious to hear how others here who don't use computers were taught to handle short SI's when diving with computer-using buddies? Obviously you could just not dive with such buddies when they head back after not waiting for a full hour, but to me that would seem like a major limitation of your system.

Option #1 ?
Or "wait 30 mins longer"

Around here it's moot. Most boats prefer you to do 60 mins, and they pay the insurance premiums (and drive you home Will they disallow less than 60 mins? Probably not, but consider the time to move the boat, fill tanks etc. and it's normal to get 60+

For shore or cave diving, less might be something you'd be tempted to do and actually be able to turn around quickly enough, but I know that after hauling tanks up the beach, the last thing I usually want to do is go right back in.

 

[amascuba]

As far as minimum deco, I haven't really been "taught" by anybody really. I've read the material that peter steinhoff has on his website and I use his minimum deco tables for recreational dives. It was a process that was self learned by listening to my body during and after a number of dives. Now have I taken advice from others? Sure, I listen to what others say and if it seems reasonable to me I try and apply it and see how it works for me.

As far as deco profiles go, as limeyx, I have been taught that one should do no more than two deco profiles per day. We used navy tables and buhlmann tables in my deco class, but we construed the tables so much that they may as well have been a bubble model based table. My instructor threw in deep stops along with the normal stops for our profiles. I was fine with that, infact really preferred doing deep stops, because in my experience I feel much better after a dive if I make a slow ascent to the surface.

 

[Ben_ca]

I use a min of 60 but more like 90 min SI... Less than 90 double the (length of) stops...
(Trained by GUE and 5thD-X guys)

In practical application unless there was some type of emergency (missing diver... bottom search) I do not see getting back into the water with less than 60 mins.... So why are we even talking about 20 min SI's?

If someone is being that agressive he's going to find a way to bend himself regardless

YNMV
"Your Narcosis May Vary"

 

[*Floater*]

I use a min of 60 but more like 90 min SI... Less than 90 double the (length of) stops...
(Trained by GUE and 5thD-X guys)

In practical application unless there was some type of emergency (missing diver... bottom search) I do not see getting back into the water with less than 60 mins.... So why are we even talking about 20 min SI's?

If someone is being that agressive he's going to find a way to bend himself regardless

YNMV
"Your Narcosis May Vary"

I dunno. When I was cave diving in the Cenotes we often did one dive followed by a briefing on the surface and then headed back for a short second dive on the remaining gas (30min SI or less). These dives were really shallow so you didn't need computer to know they were within "NDL," but the point is that short SI's do occur.

There's been other instances too when I didn't have time for a long SI. For example, I would come back from one dive and another group was there at shore heading to the water and I had the chance to join them. Of course with the boat rides and changing tanks and briefings and such it almost always takes about an hour anyway to get back in the water, but still...

 

[RTodd]

If someone is being that agressive he's going to find a way to bend himself regardless

QUOTE]

This is the real answer. GI3's argument that prior dives don't matter applied to deep dives where there will be deco with multiple gases. In those cases, the effect of the prior dive, with a reasonable surface interval, is immaterial in the scheme of things. (What constitutes a reasonable surfase interval is fairly situation specific, but in some cases would involve a very short interval.) Put it into perspective. On a 300' dive your "no deco" time is zero. So, if you deco up so that you can cleanly exit the residual nitrogen in your body really doesn't matter much for the next dive. (Taking into account other physiological effects and making sure you aren't bent before getting back into the water do matter quite a bit though and is the reason surface intervals are needed here.)

Extrapolating this to pure recreational diving does and doesn't work. If you have a long enough surface interval to wash most of the inert gas out of your faster tissues then for most types of diving, the prior dive does not matter. Plus, the minimum deco rules do get you out of the water cleaner than what most traditional tables assume.

Even without much of a surface interval, two back to back EAN 32 dives to 100' for 30 minute with proper minimum deco are not that big of a deal for a relatively fit, PFO free diver. However, eventually your body will saturate and this won't work. This works for initial dives because the traditional tables are a bit too conservative for the type of individual I specified diving minimum deco. However, you can't continuously do this all day without getting bent and doing it is a bad idea for the same reasons that you generally don't hop right back in the water for deco dives i.e. making sure you aren't bent or have signs such as fatigue that the minimum deco didn't go as well as you thought.

To get back to the original question, this is why learning the shortcut rules without a true understanding of what is going on is a bad idea. I have used all sorts of goofy rules to deco on the fly that work in very specific situations. For instance 1/4 of your bottom time -15 minutes as your 20' O2 stop time works for dives in the 80-120 minute range at around 100'. But, it only works for that specific dive. That one is easy to spot as - don't translate this to 200' dives. Where to stop using some of the broader shortcuts is what tends to confuse/ get people in trouble if they don't understand all of the underlying issues.

 

[limeyx]

If someone is being that agressive he's going to find a way to bend himself regardless

QUOTE]

This is the real answer.

This is a good answer and kind of what I was discussing (not so eloquently) with Charlie over PM.

It's also fair to note that If I am remembering correctly (which I may not be)
Charlie asked Floaters instructor about 2 back to back dives, which is much different than doing as many as you like.

 

[limeyx]

I dunno. When I was cave diving in the Cenotes we often did one dive followed by a briefing on the surface and then headed back for a short second dive on the remaining gas (30min SI or less). These dives were really shallow so you didn't need computer to know they were within "NDL," but the point is that short SI's do occur.

There's been other instances too when I didn't have time for a long SI. For example, I would come back from one dive and another group was there at shore heading to the water and I had the chance to join them. Of course with the boat rides and changing tanks and briefings and such it almost always takes about an hour anyway to get back in the water, but still...

Um, how deep are the cenotes? Shallow I think.
Change your proposition from "who wants to do 4 back to back 30 min dives at 100 feet"

to "Who wants to do 4 50 min dives at 30-40 feet with a short SI" and you'd have more takers

 

[Ben_ca]

JessH,
Are you still with us? Are you following? I hope you aren't pushing the curve without a full understanding of what you are doing...

 

[*Floater*]

Um, how deep are the cenotes? Shallow I think.
Change your proposition from "who wants to do 4 back to back 30 min dives at 100 feet"

to "Who wants to do 4 50 min dives at 30-40 feet with a short SI" and you'd have more takers

What about if you dive to 100' for 25 min on EAN32, do your min deco ascent, maybe take a few extra minutes at 10' for good measure, but then on the surface after just 30 minutes of SI everyone in your group wants to head back for seconds, same approximate depth and bottom time? What if they want to do it a third time after just 30 minutes? (because the site is just that good and time is limited and they, for this example, are using computers or something)