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

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...the goal should be to be able to estimate what the minimum reserve is at your current depth, no?...

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:

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20201018_173658.jpg


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.
 
Yes I would and yes I have. 80 - 90 is not about unusual for me. Bounce down for a great photo? No problem. Been diving since 1978 and instead of redundancy i have a great dive buddy. Bill
 
I've done 505 dives between 30 m and 40 m. I am pretty sure all these have been done on a single tank, mostly using a 11 litre (88 cf) tank and more recently on 12 litre (100 cf). For more square profiles in Sydney and nearby, I usually surface with about 100 bar. No idea what everyone thinks is a problem with this as my buddies also have similar amounts of air left from these dives. Not once in 32 years have I or anyone diving at the same time has had a problem.
 
Not sure who you cave dive with, but me and my buddies surface will a lot more gas than that. Why we dive stage bottles. Most cave dives we never even touch our back gas.

Well you must be some sort of superhuman cave diver then. Where did you learn to cave dive without breathing from your main tanks?
 
Well you must be some sort of superhuman cave diver then. Where did you learn to cave dive without breathing from your main tanks?

I used back gas in classes but after that 99% of all my cave diving has been with stages and not touching my back gas, High Springs, Tallahassee, and Mexico.
 
Yes doing that on a more or less regular basis.
Europe 12" 210Bar, quarry dive max depth 32m easily going down along the bottom/ "drop-off" and coming up the same way. Starting and ending the dive watching fishies in the shallow parts of the quarry. Total dive time upto 1hr.
In Croatia, Diving the wreck, the same 12l sometimes a 15l nitrox 28 upta 34/35m deep total dive time34/35 minutes and half a tank left (abt 100b)

All dending the situation your proficiency and many other variables.

Happy diving.
 
Was there a typo in the thread? 108ft isn't what most would consider deep, it's well within normal recreational depths. No special gear required for 108ft dives. Heck, that barely even meets the need for helium among the DIRty dudes.


I'd prefer my lp108's for this or any dive that involves being underwater. However, I wouldn't worry or even think twice about getting stuck with an al80 if that's all that was available for this dive. Same for air/nitrox. Any dive below the surface calls for nitrox. Preferably 32%. If it wasn't available, no reason not to do it on air. That said, it's been 4 or 5 years since I've had to do a dive with tire-filler.
 
Was there a typo in the thread? 108ft isn't what most would consider deep, it's well within normal recreational depths. No special gear required for 108ft dives. Heck, that barely even meets the need for helium among the DIRty dudes.


I'd prefer my lp108's for this or any dive that involves being underwater. However, I wouldn't worry or even think twice about getting stuck with an al80 if that's all that was available for this dive.

It’s all a matter of perspective. It’s not deep by the standards of many that frequent this forum, but for the AVERAGE recreational diver (only dives once in a blue moon)...100’ is deep. Ex. Myself. I have to drive 4+ hours to get to a dive operator that permits me to make a 100’+ dive.
 
Was there a typo in the thread? 108ft isn't what most would consider deep, it's well within normal recreational depths. No special gear required for 108ft dives. Heck, that barely even meets the need for helium among the DIRty dudes.


I'd prefer my lp108's for this or any dive that involves being underwater. However, I wouldn't worry or even think twice about getting stuck with an al80 if that's all that was available for this dive.
I think @Boston Breakwater chose this dive on the Chester Poling because it is known to be dark, cold, and may have brisk current. His example was also the deep dive for AOW, the divers may be less experienced
 
Another dumb ass (me) at dive # 15 in 2005, in Cayman Brac, site site called Son of Rock Monster, 126’ with AL80.
When we were diving the Brac (with my wife's OW and Nitrox instructor) we were told the Caymans essentially banned dives over 110 feet. They further claimed that they'd be checking computers and if you exceeded it they'd make you sit out the next dive.

They never checked. We also did the anchor wall which puts you out in the blue at 110 or slightly more feet. We were told that a couple minutes of your computer beeping about exceeding MOD was acceptable. Not saying this was a PADI instructor saying this or not.

I was also on Frenchies boat at the Blue Hole and people were hitting 136 feet on a single 80 on air. Amigo's was there too with more people (larger boat) doing the same thing they do every day the weather permits. The coolest thing about that day was the reef sharks.
 
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