Split from Exploration dives without a computer

[onfloat]

Are you gonna tell me you can get 90 minutes on an AL80 at 70ft while leaving adequte reserve for your buddy, and emrgency gas for yourself?

I need your lungs!

Your sac would only need to be about .2 with a 500 psi reserve.

Edited to fix math error.

 

[TheRedHead]

I guess the computer is nice if you want to "ride the NDLs", but I tend to plan my dives as square. If they become multi-level, then so be it. But I don't change my deco.

Most of the dives I do are multi-level and deeper. The only time I do a square profile is on a wreck and most of the wrecks are deep so I still run up against NDL. My computer is also a very conservative Suunto. I just recently started diving with stage bottles in Advanced Nitrox where we used Dalton's Diamond to calculate best mix and how deep and RVM to calculate gas. But Deco Procedures is all software.

 

[PerroneFord]

I audited Adv. Nitrox as well (without deco procedures) but we talked about deco outside of the class. I'm nowhere NEAR ready for an Adv. Nitrox card. I don't do a lot of square profiles either, but am creeping closer to them, and always plan my dives that way since I just use tables.

Most of the dives I do are multi-level and deeper. The only time I do a square profile is on a wreck and most of the wrecks are deep so I still run up against NDL. My computer is also a very conservative Suunto. I just recently started diving with stage bottles in Advanced Nitrox where we used Dalton's Diamond to calculate best mix and how deep and RVM to calculate gas. But Deco Procedures is all software.

 

[Thalassamania]

Here’s how I’d have approached that dive. Assuming my buddy and I have SAC rates of about 0.7. BTW: I dive regular Navy tables, with a 3 minute stop at ½ max depth and a 3 minute stop at 15 FSW and a 30 ft/min ascent rate. I maintain sufficient reserve for my buddy and I to make a dependent ascent including the two stops and an additional 2 minutes at 10 (for one step over the line, just in case). I assume that the last 100 lbs in the tank is not available.

So I go into the water with the following Excel produced table:

40 ft 200 min 750 psi
50 ft 100 min 800 psi.
60 ft 60 min 900 psi.
70 ft 50 min 950 psi.
80 ft 40 min 1000 psi.
90 ft 30 min 1100 psi.
100 ft 25 min 1200 psi.
110 ft 20 min 1300 psi.
120 ft 15 min 1400 psi.
130 ft 10 min 1500 psi.

So I’ll go into the water with this data, and my computer. I know that if I make a fairly square dive my computer will stay well within these envelopes (permit less time and/or depth).

So I’m poking along, having decided, pretty much, to go no deeper than 70 ft, stay down no longer than 50 min, and start up with no less than 950 psi. I see something cool at 100 ft. I look at my computer, I’m 25 min in to my dive and it’s giving me 15 min more. I’m at 1200 psi, that’s turn around for 100 ft. No Go!

But let’s say I was 15 minutes into my dive and had 1800 PSI remaining, my buddy had a hair more, I might go. But it’d have to be really cool, it’ll cost me about 25 minutes of bottom time.

 

[onfloat]

So I go into the water with the following Excel produced table:

40 ft 200 min 750 psi
50 ft 100 min 800 psi.
60 ft 60 min 900 psi.
70 ft 50 min 950 psi.
80 ft 40 min 1000 psi.
90 ft 30 min 1100 psi.
100 ft 25 min 1200 psi.
110 ft 20 min 1300 psi.
120 ft 15 min 1400 psi.
130 ft 10 min 1500 psi.

So, if I understand the table your using that's the minimum starting pressure in your tank.

Rock bottom on a 130 ft dive for 2 divers requires about 40 cubic feet of gas and on an AL80 that is 1500 psi. A dive like that is not DIR.

You didn't say what type of tank you were using and so your psi amounts maybe for something bigger or doubles??

 

[WaterDawg]

I dont think thats his starting pressure for the dive but his turn pressure for thoses depth.

 

[Snowbear]

A dive like that is not DIR.

Nor is doing a 130' dive on air in the first place.
Nor is counting on your SPG to be accurate down to 100psi.
Nor is doing a dive to 130' on an AL80 (though I don't think he specified the tank size?)
Nor is doing a 3 minute stop at ½ max depth and a 3 minute stop at 15 FSW with a 30fpm ascent rate
Nor is using the "NDL" on a computer as a basis for altering a dive plan

 

[lakewinni]

40 ft 200 min 750 psi
50 ft 100 min 800 psi.
60 ft 60 min 900 psi.
70 ft 50 min 950 psi.
80 ft 40 min 1000 psi.
90 ft 30 min 1100 psi.
100 ft 25 min 1200 psi.
110 ft 20 min 1300 psi.
120 ft 15 min 1400 psi.
130 ft 10 min 1500 psi.

I believe hes just stating what your turn pressure would be to get you and your buddy out with some stops.

 

[Cacia]

now that we are over here, can I call jeffg a big sissy?

Would a DIR instructor be able to dive with tourists and lead them on a deep air dive that is not DIR compliant? air to 127 for example? would that create an issue? does anyone understand the question?

I was quite impressed with Thal and his initiative on the excell spread sheet. It seems he has taken the numbers on.... a man with a plan.

does anyone else ever think in terms of the old 120 rule?

BF says that the Navy divers in Pensacola all wear sunnto stingers.

he is making the analogy about artillery, computers and accuracy and that they do the tables and then use the computer once they check the coordinates, etc mannually. I guess wind speed, temperature, multi variables in play and he argues the computers will always be more accurate...the concept a bit different, but an interesting analogy. Not blowing up a pre-school vs not getting bent. One, of course deals with accuracy and the other a limit, two different things.

I think I am getting sleepy...night kiddies.

 

[JeffG]

now that we are over here, can I call jeffg a big sissy?

You can..but it wouldn't be true.