max depth with an 80 cuft. tank

[Superlyte27]

200' for 4 minutes on Air at .5 SAC rate leaves you with 30cu' after your 9 minutes of DECO.

 

[Tigerman]

Ill go to 80 or 100 feet on an AL 80 providing the conditions are right. I will however do it at the start of the dive, multilevel my way back up and make sure I have a reasonable ammount of air when i start making my way back up.

By "right conditions" I should say that no wreck is involved, visibility is good and general risk of entanglements is minimal. Its not like ill splash around at 80 feet in 3-inch visibility at a lake filled with old fishing nets, fishing lines and other debris on an AL 80.
Come to think of it.. Only place Ill dive an al80 is on vacation as well. I have much larger tanks I normally use - steel 120ish.

 

[stargost]

In many tropical places, most of the dive clubs only provide AL80 tanks, so limited choices there.
Of course, in some of these places, the cool stuff (like big sharks or so) can be seen better when deeper than 100ft... so limited choice again.

And almost every AOW divers have the possibility to get there, whatever SAC rate, as assumption is you won't have any issue.

The fun of course is your "lesson learn" Tigerman... (I have your case in mind everytime i dive with someone I dont know and who is not a small woman;-)

What if the o-ring blew-up at 130ft, after 5min or so there, and instead of a small woman, your buddy would have been a tall guy, air hungry, already pretty exited about the big sharks? Would have been a more interesting end of the dive wouldnt it ? ...

 

[Gombessa]

Is an 80 cuft tank enough air to safely go beyond 80'? My answer is yes but not safely. Please share your opinion.

My opinion is that your answer is technically "no."

 

[Diver Tim]

It seems to me, the bottom line is you need to know how much gas you'll need to get you and your buddy to the surface from your planned depth at a safe ascent rate with a safety stop. If you've got a reasonably good idea of your consumption rate, you should be able to predict with some accuracy how long you'll have (descent and bottom time) before you reach your minimum reserve. So, if you do the planning, you should be able to figure out whether you can safely go past 80' with an AL80.

 

[Tigerman]

...
What if the o-ring blew-up at 130ft, after 5min or so there, and instead of a small woman, your buddy would have been a tall guy, air hungry, already pretty exited about the big sharks? Would have been a more interesting end of the dive wouldnt it ? ...

Indeed it would.. But then my turning point would also be set at a higher ammount of gas, or maybe even "lets not go there"..
Thing is though, **** DOES happen when diving and everything we do is, wether we like it or not, calculated risk.

 

[hg frogman]

Is an 80 cuft tank enough air to safely go beyond 80'? My answer is yes but not safely. Please share your opinion.

One cannot generalize as you seem to do. It depends on :
- your Surface Air Consumption (SAC), experience, streamlining and fitness
- your buddies SAC, experience, streamlining and fitness
- conditions prevailing (and notably the current and visibility)
- is the dive an open water dive with mild deco or within the NDL, or is it more severe ?
- ...

Fortunately, experienced buddies with low SACs (eg 12 liters per minute) can often plan and do dives deeper than 30 meters/100 feet safely with an Al80. I wouldn't recommend it though for any kind of "material ceiling" dive (cave or wreck penetration) where one may get stuck for an unpredictable amount of time (contrary to open water deco diving which has a ceiling predictable both in depth and time) and for which, then, one needs redundant tanks, with rules about carried gas that can be much more severe than the "rule of thirds" (see below).

Some remarks :

- It's advisable to set and use rules like, for instance, "when tank is half full one must be at 12 meters/36 feet or shallower".

- Limits of Al80s for deco dives. If your buddies and you are experienced and know well each other, and each of you has a low SAC, and each of you shows consistently prudent attitude ("plans the dive and dives the plan"), and the conditions are OK, and each of you uses an Al80 because you checked it would be enough for the planned dive, and your dive is an open water (no penetration) deco dive with moderate hang time (say less than 10 minutes), even then it's advisable to systematically plan and make sure that each of you has more than one third (of the full tank capacity) of air left in his/her Al80 after completion of the stops. This third is for emergencies, eg sharing air with one buddy during ascent and stops in case of an equipment failure at the end of the bottom time (worst case). If one of you doesn't have this third left, Al80s were too small for the dive.

- To avoid blowing the valve O-Ring after 5 minutes underwater (can happen with O-Rings too soft), use DIN valves and regs. But these valves are not available everywhere.

- Any extra stuff you carry underwater increases (sometimes dramatically) your SAC because it increases your weight/inertia and reduces your streamlining. Make sure that the "plus" of what you wear or bring with you underwater more than compensates the "minus".

- There are physiological limits for how low each individual's SAC can be (eg size of the lungs and global weight) but SAC most of the time reduces significantly with improved training, experience, streamlining and fitness.

 

[miketsp]

Is an 80 cuft tank enough air to safely go beyond 80'? My answer is yes but not safely. Please share your opinion.

Simply put, where are the statistics to back up your claim?

Thousands of dives are done by recreational divers, below 80', every day all around the world and these dives rarely figure in the accident reports.

On every dive trip I've been on for the last few years I've done at least a couple of dives below 130ft using AL80s AND respecting rock bottoms for myself and my buddy. Many of these dives don't even incur any deco obligation.

One of my favourites is the Cueva Azul in Cuba - the sensation when you come out of the tunnel into the rich blue of the wall at 40m+ is indescribable.

hotel el colony .com - Cueva Azul Dive Site in El Colony

Here's a typical profile from one of my dives on this site.

You don't even go into deco and the ascent is long and slow. We both got back on the boat with over 80 bar.

 

[GrumpyOldGuy]

Is an 80 cuft tank enough air to safely go beyond 80'? My answer is yes but not safely. Please share your opinion.

If you have been trained right, you know what your rock bottom reserve is based on real SAC rates and you don't need to rely on a rule-of-thumb like the 80/80 rule that is really just a line in the sand.

The 80/80 rule is similar to the end-your-dive with 500PSI rule often quoted. Both are simplistic rules for people too lazy or ignorant to take the effort to calculate their reserves properly.

 

[SkimFisher]

I've done it as I'm sure most of us have. It's not ideal, but it can be done. I prefer to use the right tool for the job though....