Are Single 80's a Smart Choice Deeper Than 60 fsw?

[Rhone Man]

When I was in Truk, when we dived the San Francisco Maru, they sent down a few DMs to sit on the superstructure and watch to make sure no one did anything stupid.

We were all wearing doubles on the deck (about 165 fsw, although some holds went down to 185 fsw). They were wearing Al 80s, except for one who had a 72 (superstructure was about 145 fsw).

They were all superb divers, but I did think to myself: how much gas will they have to actually help out if there really is a problem at 165 fsw or deeper?

 

[TSandM]

Insta-gator, that works out to about .4 cfm, which is a fairly low gas consumption rate for an adult male, but not unknown. It suggests you are either very fit, an efficient and relatively slow-moving diver, or skip-breathing

 

[MXGratefulDiver]

A decade or so ago in Cozumel there was an operator that would let divers do 200' dives on a single AL 80 and then print them up a nice certificate with the max depth.

The owner of one of the shops I worked with did this and later went back to do a 225'
dive - also on a single AL 80. The fact that he was a shop owner and an instructor does not change the fact he was an idiot.

He had a print out of the dive profile and gas remaining from an air integrated computer, and from the profile it was obvious it was a bounce dive with only about 30 seconds spent at max depth, and with lots of gas left even after a failry slow ascent from 100' on up, but that just further obscures the fact that any delay would have resulted in an OOG incident and or a serious missed deco situation.

What was worse about these dives is that the guide stayed at 100' and had only visual contact with him.

There's a thread in the A&I forum about a fellow I once knew ... and considered a friend ... who went on a dive like that. He was using a 100 single, and went to about 210. Everything went fine until, on the way up they realized that one of their divers was missing. Chad went back down and found him ... sitting stupid ... on the bottom at about 205. Chad grabbed the guy and pulled him up off the bottom and started kicking toward the surface. At about 160 feet, Chad ran out of air ... because he was working so hard trying to bring his fellow diver up with him. His last act was to inflate the guy's BCD (apparently the guy was too narced to help himself), and let go.

Steve ... the fellow Chad rescued ... rocketed to the surface and spent the night in the local chamber. Chad wasn't so lucky ... they found his body 10 months later, half-buried in the mud at 205 feet.

It's easy to do a deep bounce dive on a smallish single tank ... as long as nothing goes wrong ...

... Bob (Grateful Diver)

 

[MXGratefulDiver]

Insta-gator, that works out to about .4 cfm, which is a fairly low gas consumption rate for an adult male, but not unknown. It suggests you are either very fit, an efficient and relatively slow-moving diver, or skip-breathing

I average out at about .43 CFM ... and I'm an old, fat dude ...

... Bob (Grateful Diver)

 

[GrumpyOldGuy]

I bounce between .38 and .45 also I am old and fat (220bs) and don't skip breath. I am relaxed in the water.

Obviously the OP baited with the 60' in the title and then beat the numbers into submitting to support his idea with a 100' square profile. The point that at some depth the AL80 is a poor choice is taken, the depth depends on your SAC and the SAC of your buddy. If you are too lazy to run your own rock bottom calculations then go with the 60' limit. If you know your rock bottom, then you know if an Al80 is adequate for your dive.

 

[drbill]

I've had no trouble doing dives with max depths of 100-150 ft on a single Al 80 (but I always carry a large pony when going to those depths). On a 120 I would go to 200 ft on a single tank (with pony). However, very few of them were square profile dives since the underwater topography off Catalina usually allows for gradual ascents up the slop to shallow water for any deco obligation. Is a single 80 a smart choice? Not without redundancy or a good buddy.

The SAC rate you use does seem awfully high... but then I've seen divers that would probably be in that range.

 

[PfcAJ]

I'm not a huge fan of single 80s on deep dives, but the OP made an error that (imo) overinflates the gas requirements needed to surface.

Half the max depth is 50ft, but the average depth on ascent is shallower. No matter if you do a min deco ascent, or a safety stop, your ascent will be quicker on the deep phase (30fpm to either 50ft or 15ft) and then 10fpm thereafter if doing a min deco ascent. This really bumps the average depth quite a bit shallower.

Just somethin' to think about. I'm all for being conservative, but I'm also not all about planning myself out of dives.

The OP's method for deriving minimum gas is certainly conservative and easy to calculate, thats for sure.

 

[ianr33]

I don't see anything wrong with an Al 80 at 100 feet in the right conditions. With a SAC of around 0.6 ( most divers can do that in tropical waters on a lazy dive) You will still have 1500 psi after 15 minutes. Enough bottom time to make it worthwhile and plenty of gas for emergencies.

There must be 100s of dives done every day in Cayman like this. 15 minutes at 100,head back to the mooring pin in around 50 feet of water ,hang around there until gas is down to 800 or so then ascend.

Cold,dark,currents it's a different story though.

 

[TSandM]

Well, to defend Errol a bit, where he dives the dives are deep and utterly square profiles. There's no option of shallowing up a bit to drop the rock bottom requirement. In that kind of setting, an Al80 really isn't a great choice, unless you have two divers with very low gas consumption rates who are also experienced enough that they aren't going to be rattled if one of them has a clogged dip tube or freeflow. I don't know a whole lot of people who could keep their consumption normal in the face of that sort of thing, although I know a lot of people who probably wouldn't reach 1 cfm in that setting.

 

[rjack321]

unless you have two divers with very low gas consumption rates who are also experienced enough that they aren't going to be rattled if one of them has a clogged dip tube or freeflow. I don't know a whole lot of people who could keep their consumption normal in the face of that sort of thing, although I know a lot of people who probably wouldn't reach 1 cfm in that setting.

Check out what happened to Lamar (and Mark) from a bad air fill in his diluent bottle. I don't think there's any question Lamar Hires is experienced enough to keep his head screwed on straight when the poo hits the fan.
The Deco Stop

There's more that can go wrong with even the most experienced buddies which renders them effectively useless hoovers.