Which tables do I use?

[Rainer]

I've been comfortable running the following numbers (up to 4 dives a day, all on 32, min deco ascents, doubling shallow stops for repetitive dives *and* dives past 80', with 60-90 min SIs):

40 Till boredom, cold, or lack of gas.
50 140
60 80
70 55
80 45
90 35
100 35 (probably a bit aggressive)
110 30 (ditto)

These numbers are derived from applying the 20% credit to a backed off 120 rule.

 

[Reg Braithwaite]

Just an FYI: UTD's training materials seem to suggest a "30/30/30" rule of thumb for minimal deco diving: 30 minutes at 30 metres using 30% O₂. From this "baseline" you can make adjustments: 5 minutes for each 3 metres either way, although things stretch out at shallower depths.

 

[Rainer]

I find the UTD (32) table seriously over-conservative. For example, at 60', it gives basically the same time as I'd do on air. At every depth it's more conservative than the PADI 32 table. I know what kinds of divers, stops, and ascents the PADI table has to cover (basically every possible diver); I'm not looking for something even more conservative than that.

 

[rjack321]

I've been comfortable running the following numbers (up to 4 dives a day, all on 32, min deco ascents, doubling shallow stops for repetitive dives *and* dives past 80', with 60-90 min SIs):

40 Till boredom, cold, or lack of gas.
50 140
60 80
70 55
80 45
90 35
100 35 (probably a bit aggressive)
110 30 (ditto)

These numbers are derived from applying the 20% credit to a backed off 120 rule.

Yeah those are a bit aggressive for me, but I'm like Mr. Bendy too. So I could see how they would probably be fine for the average to better off-gasser.

I know what kinds of divers, stops, and ascents the PADI table has to cover (basically every possible diver); I'm not looking for something even more conservative than that.

Yeah most of them are probably passed out on the boat ride home too.

Actually we aren't all that far apart. If you're in MX (or some rarer places in FL) diving 32% or 30/30 in caves you do start to wonder about the 40ft times tho. I have done 150-160min dives there at 35-45ft averages. That adds up. You can't really surface 'immediately' anyway so doing 10mins (or more) of shallow deco is pretty easy.

Not living down there its hard to have enough dives at those kinds of increasing durations to get a good barometer of personal response.

 

[RTodd]

For the really shallow stuff in Mexico, keeping hydrated, watching your exertion, etc. is far more important than spending a few extra minutes at 10'. I have done some ridiculous times at 40' average and surfaced basically just slowly following the last part of the cave up and had no issues. On the other hand, I have felt like crap and aggrevated prior injuries on much shorter dives where I did something stupid like forgot my second water bottle and entered the water on the edge of dehydration or rushed to get multiple gavins, etc. out of the water immediately after surfacing.

 

[rjack321]

Since I'm not scootering in caves, I am pretty much always going to feel crappy after swimming for >2 hours despite the 40ft depth. For me, the ~10 mins at 10ft is more a chance for an extended rest than a deco stop!

 

[DaleC]

Thanks all again so far. I will have to chew on some of those numbers for a bit (ha ha you got me there Lynne. I forgot about the DIR MOD limit of 100fsw).

rjack, here's the problem I have been having to date with this type of dive (a fairly common profile for me actually).

This is my recent profile for the Nakiya, a shore access wreck with a surface swim approach and an up slope return to shore:

When I plan the dive (PADI tables) I see that I can stay at max. depth (100fsw) for 30min's using 32% EAN.

When I dive my computer confirms I am within the NDL and I leave the wreck after 12 minutes (or so).

Afterward, when I use a square profile I enter 100ft. for 38 minutes which puts me so far past the NDL I can't even guestimate my needed SI. I know it's a false outcome but I haven't learned how to get around plotting a profile like this.

I was hoping there was some kind of voodoo I hadn't heard of yet :depressed:

 

[Bismark]

depth averaging..............

 

[ae3753]

I was hoping there was some kind of voodoo I hadn't heard of yet :depressed:

MDL diving is two parts:

1. MDL tables
2. Depth averaging

If there is "voodoo" it's how you use these items. The MDL numbers I'm comfortable with are the same as rjack321.

 

[TSandM]

One of the things Joe Talavera talked about during our Rec 2 class was where to start the clock. We started the clock at 50 feet (since the ongassing above that is really minimal). If you start your clock at 50 and end it at 50, you have about 15 minutes of time at depths where you are really accumulating nitrogen. 15 minutes is a permissible time at 100 fsw, and you were at or above that the entire dive.

Although I was not taught this by anyone, I tend to treat ANY part of a dive at or above 30 feet as decompression, not nitrogen absorption. So the way I look at it, you can pretty much throw away all the time spent shallow, in terms of figuring out where you sit on the tables. (Please recognize that this is my personal approach, which began with reading a thread by Uncle Pug which has since been lost, where he posited the idea of spending as much time above 2 ATA as you spend below 3, and it made a lot of sense to me.)