Inexperience resulted in OOA at 66 feet (long)

[Goose75]

On the original topic, I know that I am grateful for every bad experience that ended well. Most of mine happened as a newly certified diver following the 'experienced diver' or instructor/DM. I found very quickly that hundreds and hundreds of dives may mean a diver is lucky instead of skilled.

As for OOA, my wife had an instructor run low on air during a class and had to share. My wife assumed this meant dive over, time to ascend but the instrutor signalled her to stay at the bottom. They came up later and the instructor explained that she didn't want to breath down her pony while waiting for the two missing students. The two missing students were me and a friend whose dry suit burst a seal. We aborted and waited for a minute or two for the others at the surface before getting him to shore and warmth.

 

[TheRedHead]

I did two deep dives for the PADI specialty yesterday. Dive plan for the first one was to go to 120 feet. The briefing from my instructor talked about no deco times and using the tables and the wheel to plan them. There was some discussion about being aware of how much faster you use air at that depth.

Everybody, including the divemasters assisting the class, was shocked when I told them I had calculated rock bottom for 120 feet and it was half the air I was carrying. I went on to have a discussion with one of the divemasters about calculating the expected air consumption for the dive we planned to make sure I had enough air with me to do it. She had never calculated her rmv, had never done rock bottom calculations, and was astonished that I was running those numbers.

I don't know why this sort of thing isn't included, if not in open water, at least in the AOW deep dive, or at minimum, in the deep dive specialty. I wouldn't have this information if it weren't for NW Grateful Diver's gas management seminar I attended.

My husband refers to these ideas as "DIR stuff". Sad to think that intelligent management of one's life support would be viewed as solely the province of technical divers . . .

SAC and gas management were included in the SSI Deep course. At 120 feet, I would run up against NDL before I reached rock bottom. The calculations would get very complex for the typical rec reef diver doing multi-level diving. It would be more applicable to wreck divers and extended range divers. Say you're diving in a new location, Cane Bay Wall, a shore dive, which requires you to descend to 25 feet and swim out over patch coral until you reach the wall, which plummets down beyond diving limits. You spent 10 minutes swimming out and your depth has increased to 50 feet before finding the wall where you descend to 120 feet. If you spend 7 minutes at 120 feet, ascend to 80 feet for 10 minutes, then up to 50 feet to start your return trip, when you do reach your new rock bottom? And how to do you keep a running rock bottom tab at each depth? How much time do you have to explore the shallow part of the reef which will become part of your safety stop? If you're going to make the concept really work, your buddy also has to calculate rock bottom and you use the number of the team member who has the worst gas consumption.

Many divers couldn't make those calculations on the fly. Yet most divers make those types of dives without incident because they learn from experience from making deeper and deeper dives over a period of time about how much gas they need.

You're going way over the top, TSandM. Pretty soon we're going to be reading about you diving doubles and pulling china from the Doria.

 

[TSandM]

Pretty soon we're going to be reading about you diving doubles

No, you're not. I can barely walk with the steel 95's I'm diving now

Admittedly, recalculating rock bottom repeatedly, on the fly, during a multi-level recreational dive, isn't particularly reasonable. But I think if you have a known dive profile (which we did) with two depths involved, it's not UNreasonable to run a set of numbers, if for no other reason than to get impressed by how much air it takes to get back up to the surface if things go badly haywire. And certainly, somebody ought to mention such ideas!

 

[Snowbear]

Admittedly, recalculating rock bottom repeatedly, on the fly, during a multi-level recreational dive, isn't particularly reasonable.

Maybe not right now, but after a few more dives, you will likely find that it's really not so complicated and seems to happen almost "automatically"

 

[Scuba_Steve]

Huh?

There's no "re-claculating" RB's on an NDL dive.

Your at 100ft use XXXXpsi, Get to 60ft use XXXpsi no calcs, simply switching to another pre-determined number.

Now if you want to talk about re-calulating NDL's on the fly on a ML dive, you may have a valid point.

Micro-mangaing the snot out of RB's are needless and a waste of time IMO. Using 700PSI at 60ft using a ALU80 if that's what you want, but attempting to gain some sort of mathematically more accurate number at 45ft? Why? Did I miss the KISS system of just using 700PSI and calling it "more safe". LOL Rock is Rock, leaving a couple extra pounds really is OK. Besides, how accurate is you gauge down that low? Down to 10-50psi?? Didn't think so.

TS&M:

One of the best things about GUE is how they simplify things so well. As I recall when we did the RB's under various circumstances, we did the math "long-hand" so everyone understood how it's done, and then they tossed a neat little chart at you and told you to put it in your wet-notes. Now if you need to alter the numbers you use (Slightly), you know how, but the fact remains they give you a number for a given tank for 0-60ft, and 60ft-100ft. The simplicity is decidely GUE-like, and took possibly 30minutes for us to go through.


Regards

 

[TheRedHead]

No, you're not. I can barely walk with the steel 95's I'm diving now

Admittedly, recalculating rock bottom repeatedly, on the fly, during a multi-level recreational dive, isn't particularly reasonable. But I think if you have a known dive profile (which we did) with two depths involved, it's not UNreasonable to run a set of numbers, if for no other reason than to get impressed by how much air it takes to get back up to the surface if things go badly haywire. And certainly, somebody ought to mention such ideas!

I'm curious to know how much air you actually used vs. your predicted use. In my deep class, we discussed and worked out problems for turn pressure. It was more of an empircal approach using the diver's SAC and other factors like expected currents. For me, Lamont's rock bottom turn pressures (computed by Ayisha) are extremely conservative. 1900 psi is a lot of air at 30 feet. I could dive for an hour with 1900 psi. You can make a CESA at 30 feet. On a typical Florida Keys dive at 30 feet, you go out against a current and return with a current. Your gas consumption going out is greater than coming back. With such a rigid formula you are either going to make extremely conservative dives or carry enough gas to herniate a disc.

According to a series of articles in Undercurrents caled "Why Divers Die", the number one reason for OOA incidents is divers failing to check their guages. And without a doubt, the number one reason for diver death is plain old panic. The original topic of this thread was really a mistake in making a "Trust Me" dive and even the inexperienced divers knew there was something badly wrong with the way the dive was proceeding.

You guys in the Northwest dive in more extreme conditions and I'm sure it that there is a psychological effect from deep, dark and cold as opposed to deep, warm and I can see the surface at 130 feet. I'm not a reckless diver, yet I'm more inclined to plan my profiles based on my diving experience rather than a rigid formula which is over conservative for my air consumption and the conditions in which I dive.

I had a 2nd stage freeflow at 50 feet which could have resulted in an OOA. I just swtiched to my octo and made a 30 ft per minute ascent to the surface with my buddy. It was no big deal. This happened right after I had my reg serviced and I've read that it is not uncommon.

The stuff they teach in rec diving courses works for most recreational dives. It's when you push the limits you need more conservative rules. I find it ironic that Shek Exley, the originator of the Rule of Thirds, died on an extreme solo dive to 900 feet.

 

[TheRedHead]

Huh?

There's no "re-claculating" RB's on an NDL dive.

Your at 100ft use XXXXpsi, Get to 60ft use XXXpsi no calcs, simply switching to another pre-determined number.

Ok, you're at 50 feet in a relaxed dive and you hit your rock bottom while following a sloping contour which will take you to 25 feet in 2 minutes, halving your air consumption. Do you make the ascent and a long swim back to shore or do you use your brain and follow the contour to shallow water where you can use the decreasing depth to complete your safety stop and get you close to shore?

 

[Scuba_Steve]

Ok, you're at 50 feet in a relaxed dive and you hit your rock bottom while following a sloping contour which will take you to 25 feet in 2 minutes, halving your air consumption. Do you make the ascent and a long swim back to shore or do you use your brain and follow the contour to shallow water where you can use the decreasing depth to complete your safety stop and get you close to shore?

I'd use my brain and follow the appropriate rock bottom (predetermined) number for the dive you will be doing AKA :All usable, 1/2 or 1/3.

Nothing wrong whatsoever with being conservative.

 

[TyTy]

It only took me one time surfacing with 350 or so in my tank when the DM had signaled that it was ok when in my head I knew I wouldnt hit the surface with 500 unless I headed up. After that dive I just tol dmy buddy, when I need to go up Im headed up, Im waving goodbye to the DM and we are gone. We had to do that on the next dive and I hit the surface with JUST over 500psi. They came up 5 or so minutes later and he just looked at my gauge and walked off.

That is one big thing in this sport, dont assume ANYONE is always right, even yourself. Take the information that you have, the information others are giving you and make a decision, if you arent sure ALWAYS aire on the safe side, 5 or 10 minutes of bottom time isnt worth the risk!

The main thing is to have the confidence to make the decision and do it. Dont worry about getting proded for heading up too early, if you get kidded about it just say 'ha, I was a little nerrvous and wanted to play it safe.'

 

[TSandM]

Somebody please correct me if I am wrong, but if you are at 50 feet and reach your rock bottom plus reserve, what you know is that, if you stay there any longer, you do not have enough air to get you and your buddy to the surface, making all appropriate stops. If you then move up to 25 feet, you then DO have enough to do that from the new depth. I think that's why Scuba Steve was talking about knowing a few "set point" RB values, which was a good tip for me. I can easily memorize a few numbers to give me guidelines for the dives I typically do, which don't involve a great range of depths.