Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

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So you bounced to 40m, were riding NDL, stayed for 57minutes underwater and surfaced with almost a half full AL80. Sure.

I've done to 45m and rode NDL to around 3 mins back to around 20m then went to around 15m - 10m finished with 80 bar on an AL80 with 200 bar start after 55 mins. I went to get dropped camera equipment for a lass on her morning dive at 8am so this was my second dive of the day. We ended up doing 70 mins on the dive the last 15 mins around the 5m mark on a reef taking some photos.

I'm pretty decent on air. I know some dive masters in the Philippines who are better than I am on air.

 
No.

Rock Bottom gets re-calculated when you safely ascend to a shallower depth. New depth, new rock bottom.
1 Minimum Gas gets calculated for a max depth if you are doing a MD ascent. That's it.

Lamont had an excellent essay on calculating the early RB on SB many years ago. He then removed it and replaced it with the next version of rock bottom, which was more conservative. That essay is probably still on here. I had a copy of both on a very old hard drive and backup (2004 or 2005?). It would be a PITA to search for them.

However, this is a very old mac-tacked table (both sides) I made from the original RB way back when, with some moisture damage:

View attachment 618930
View attachment 618931

I never made a table of the next version of Rock Bottom as it was pretty much a non-starter for a single tank, and that is when the advice came out to limit a dive depth to the cf of a tank, for example, an 80 cf tank to a max depth of 80 feet.
Not sure how it evolved after that when other DIR groups ran with it.
That is amusing!
 
Hi @Scuba Lawyer

I meant to ask, how long were you on the bottom, no stop or some deco?

On the bottom long enough to take 2 or 3 photos of the WWII submarine net that lay in a heap there (while manually advancing the film in my camera housing :) ). It was a stupid thing to do but back then we were immortal. I do recall looking at my plastic set of NAUI tables on the way back up the wall and being somewhat dismayed they capped out at 190'. Did some mental math and stopped at 30' for a minute then 20 for a while and then 10 until we ran out of air. Nothing very scientific about it. No ill effects. I do not recommend anyone follow my example. :)

I did give a lecture on that dive in @Sam Miller III 's Advanced NAUI class upon my return.
 
Thanks @Scuba Lawyer

Not that I would consider doing this dive, or advise anyone else to, but interesting to think about it. My 2 computers will only do an NDL plan to 190 feet also, give 5-6 minutes. With a quick descent, 5 minutes on the bottom, and a normal ascent, looks like I would be doing 2 minutes at 30 feet, 2 minutes at 20 feet, and 6 minutes at 10 feet, for a run time of 25 minutes and about 43 cu ft of gas. Of course these are using my computer settings. I would do as you did, and burn my extra gas at the last stop to get my SurfGF down to something reasonable. This scenario takes advantage of modern dive computers.

So, nearly 40 years ago, with a Naui table and considerable knowledge of diving, you did an ascent nearly identical to the one I posted above :)
 
Hello. I was thinking back over the years. I worked for a Dive shop years ago as a Divemaster.
We did our deep dives on the Chester Poling off Gloucester, Mass. for the P.A.D.I. Advanced Open Water Course.
At high tide the the wreck sits in 108fsw. It always amazed me that people would do this dive "Normally." on single aluminum 80's without any type of redundancy.
I always thought it was insane???? Divers would come back on board with extremely low pressure readings on their gauges. Too me, it left no room for error, or any type of contingency whatsoever. At that time, I was diving with an Aluminum 100 cubic 3300 P.S.I. (Air.) with a 30 cubic pony bottle.(Air.)
20 years ago the shop did not have "Nitrox." (This is not an enriched air scenario.)
Staying within N.D.L.......I don't care how long you've been diving, or if, your'e the best breather on the planet your max bottom time is approximately 18 to 20 minutes, at 100fsw, not including the 3 min Safety stop.
So, I was curious? The question is: Would you personally make this dive, staying within N.D.L. on air........No redundancy?
Cheers.
Let's do the math here. Sorry, I will speak in metric. With a 15l/min SAC (which is pretty average for an experienced diver), a 12 liter steel cylinder at 200 bars gives you:
- 30 minutes breathing time at 30 meters and you still have 50 bars in your tank.
- 24 minutes at 40 meters and you still have 50 bars in your tank.
Given that the NDL at 30 meters is 20 minutes and 5 minutes at 40 meters, you have plenty of time to do your safety stop at 5 meters or help your buddy breath.
I made myself a little table that helps me with the big picture. I can change the tank capacity, the tank pressure and the SAC and all the other data is automatically calculated.
 

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  • Table consommation air.xlsx
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Let's do the math here. Sorry, I will speak in metric. With a 15l/min SAC (which is pretty average for an experienced diver), a 12 liter steel cylinder at 200 bars gives you:.

A lot of experienced divers SAC rate is 10l/min or less but calculations at a higher rate are better.
 
A lot of experienced divers SAC rate is 10l/min or less but calculations at a higher rate are better.
I am at 11l/min but I figured that 15 would speak to more people :)
 

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