Shallow Decompression Dives

[Jim Lapenta]

SEI covers deco procedures using tables in Open Water class. Depending on what you mean by shallow. Since OW divers are suggested to limit their depths to 60 feet it seems that your examples fall into the advanced OW categories. I cover deco to the point that if one of my OW students never took advanced and merelyu extended their depths by experience and with a mentor they could plan a deco dive using the SEI tables which are based on the new Navy tables and include deco schedules to 130 feet with deco being done at 20 feet. Ranging from bottom times of 200 minutes at 40 feet to 30 minutes at 130 feet. So if one of my divers wanted to do a 60 foot dive for 70 minutes they would know how to use the tables to figure an ascent time of 1:20 to the 20 foot stop and then 23 minutes there.

I would of course not recommend this be done but if they had the gas and enough experience to make the dive then they would know how. I also would encourage them to take my advanced class where more procedures are covered along with gas management.

 

[Blackwood]

Yeah, that's true but what I was trying to get across s that not many divers are trained in ratio deco and most of your run-of-the-mill tek buddies are probably going to want to cut tables and plan the dives along more traditional lines. I'm not sure that paradigm gap would be easy to bridge. It's not a judgement call either way.

R..

Even within the "DIR Community" I don't think that Radio Deco (modified Buhlmann) being used as the primary way of deco planning is the norm. My dive group uses it, but many more use Deco Planner (Buhlmann), Vplanner (VPM) or other software.

But assuming GUE/UTD divers were exclusively trained with Ratio Deco, I don't believe that would preclude their diving with others, or others diving with them. A schedule is a schedule. Anyone can follow it. Once it's agreed upon, figure out how much gas you need and go diving. I don't really see a large paradigm gap. I'll dive a Vplanner or a Buhlmann schedule. I may suggest a slight re-shaping of the profile (extending the bottle-switch depths, etc.), but in the end, a schedule is a schedule regardless of how it was derived.

 

[Diver0001]

Ok, what you seem to be saying here is that you can fold ratio deco plans into plans made with other algorithms in a similar way you'd fold a Gap plan into one cut on Vplanner....

sounds logical. Maybe you're right then. Even if you approach the horse from two different angles, it's still a horse....

BTW, I didn't know that not all DIR divers were using ratio deco. I thought that was one of tha hallmarks of the system. You taught me something new just there....

R..

 

[AndyNZ]

Ratio deco is really (as I understand it, at least) just a curve fitting exercise - it's a simple set of rules that provide you with stops that approximate those that would be given by a deco model such as decoplanner. The advantage is that the rules are simple enough to allow you to calculate the stops "on the fly".

CMAS and BSAC cover deco diving in relatively entry-level courses. Echoing what has been said before, deco isn't rocket science - but for anything other than a few minutes here or there, it's worth having a bit more knowledge, irrespective of if you're diving shallower for longer or deeper.

 

[Blackwood]

BTW, I didn't know that not all DIR divers were using ratio deco. I thought that was one of tha hallmarks of the system. You taught me something new just there....

R..

I have no formal training from GUE, but my understanding is that DecoPlanner is still their primary decompression tool with Deco On The Fly ("Ratio Deco") being emphasized for contingency usage.

 

[TBURKE]

The Old Fart's $.02
When I learned to dive. "83" We used the Navy Tables. I am a NAUI trained diver. We were taught that every dive was a deco dive.
The way the tables were written, you ascended at 60ft/min or 1ft/sec. If you were coming up from 40ft, your total deco time was 40sec.
If you were at 60ft and stayed for 70min your total deco time was 3:00min. That worked out to 50sec to get to 10ft, a 2min stop, and 10sec to get to the surface. It was a different mind set. It made things easier and deco wasn't the boogie man hiding under your bed at night. We also started extending our shallow stops because it made us feel better. We would even do a stop weather we needed one or not. This was before DAN gave it's blessing to safety stops.
I once saw a PADI instructor yell at a former student for doing a safety stop. He kept calling it "deco" and was threatening to pull her card.
As far as our air supply was concerned, we all used pony's and most of us had doubles.

 

[Deefstes]

This is a fascinating thread. Thanks everybody.

 

[ScubaSteve]

Thank you for the posts so far everybody. I think there has been some great information shared so far. Just to confirm, one poster asked about the depths that I was asking about and my question basically revolves around diving at less that 130 fsw or ffw but for durations which would exceed NDL diving.

This is a fascinating thread. Thanks everybody.

Deefstes, it was actually your post about your CMAS AOW which made me realize that this had never been discussed as a topic (that I was aware of). And since I was sure that many (even experienced) divers want to increase their bottom time but have little interest in taking their diving to "that level" with deep dives, I figured I would post the question so it would be here for all to read. Heck, there might even be some ulterior motives for me posting as well

 

[Deefstes]

Deefstes, it was actually your post about your CMAS AOW...

Yeah, I figured that much but I was too shy too admit to it openly

To me this is a bit of an eye opener as it became clear to me since that most members here (and I would surmise then most scuba divers) consider staged decompression diving to belong under the banner of technical diving and not just recreational diving. I was under the impression that deco diving is simply another tool in the "advanced" open water diver's arsenal.

It reminds me of an occasion during my first diving trip to Sodwana bay. There were a number of my friends present, all of whom are AOW qualified. They were kitting up for dive which was going to be a 30m dive which means that I was not going to join them. I listened in on their dive planning though. The DM went through the usual stuff and then said something along the lines of
"This will be a 30m dive leveling off to 20m after 15 minutes. Check your computers so that you don't go into deco... oh what the heck, you're all advanced divers, let's go into deco"

At the time I saw them walk off towards the boat thinking by myself "Wow, there goes the masters of the scene". Relating this now I'm thinking "How immensely stupid is that? Where was their gas planning? What were their critical pressures?" Surely that's not the way deco diving is meant to be approached?

 

[Rhone Man]

The other thing that "casual deco" divers usually lack awareness of is the need for redundancy. It is pretty easy to go to 100 feet for 25 minutes and conduct short deco on a single 80 cu ft tank for anyone with a half decent SAC rate. But if your SPG blows or you get a sudden free flow, and you don't have the necessary gas redundancy, you can easily find yourself travelling up a certain creek with a shortage of paddles...