Faith diving and magic?

[lowviz]

I swore to myself that I was keeping out of this, but in honor of the guts it took to post your screw-up, you get my best shot at answering what you actually asked.

.................If you are still with me, then here is the reason for the post, how much faith do you put in your computer?............

Tons and bunches. But only because I have a really nice computer that doesn't mind if I verify everything it tells me.



Plan your dive and dive your plan, but know that all plans can turn to crap. No matter how good you are, your best plan can turn to crap. When they do, you will find yourself with more than one issue that demands all of your mental capacity. So before I dive, I have a plan to free up my mind for what is immediately life threatening. For the dive in question, you were distracted from dragging your wife out of her dive while madly trying to guesstimate if you had the gas to pull it off. Let me guess, your mind was madly flipping between how to interrupt her and doing gas calculations. If so, you were just wasting precious time hoping that an answer would appear.

It helps me focus if I can determine the real, no BS, bitter end of my dive. So I pick: most aggressive algorithm, just made my stops on backgas, backgas is air, a realistic RMV, hit the surface with 0 psi. I use the US Navy Diving Manual Rev. 6 April, 2008. Chapter nine for the air deco tables. Compare them to anything, they are aggressive.

What to do:
Using all of your backgas load, calculate an OMG dive for each 10' increment around your typical dive depths and use one of those plastic label printers to make about 8 strips for your wrist slate. So now you have 8 dive plans, any one of which exactly uses up all of your gas by the time you clear your last deco stop.


Your dive slate should show you at a glance: Max Depth, Max bottom-time, all stops and their depths, and total run time. Since each dive strip is calculated to use all of your backgas, you are screwed if you violate Max bottom-time for any given depth. A quick glance frees up your mind for other pressing issues...

So now what if you surface in deco?
If I am asymptomatic and can get gas within a minute or two, I'll suck it dry at 15' if it is pure O2, or do the ten minute IWR omitted stop routine if it is air. Here is where I can be stopped, no donation, I'm getting out. Captain's choice.

And now, back to the hockey game.

 

[kanonfodr]

SailNaked: Thank you for being forthcoming in the face of the potential for these naysayers to come out and jabber. You have officially been taught a lesson so carry it with you, and if you're an instructor, use it as an anecdote in your classes.

Recreational DCs really give you both barrels once you get them into deco. Think of them as being programmed by lawyers, these things are giving you way more deco time than you probably really need. The reason: to avoid a lawsuit. That's why I keep mine in Gauge Mode, plan my dive, and dive my plan. But things happen, especially with a camera in your hands, and when those things happen, your computer can give you a nice slap on the wrist.

I would urge you that, if you are interested in learning appropriate ways to manage these situations, and ultimately prevent them, you might want to take part in an introductory decompression course along the lines of TDI's Decompression Procedures, probably adding Advanced Nitrox with it since both courses seem to complement each other very well. Learn the theory, the protocols, and the planning involved. Then if you really want to stay longer you can, and safely.

Peace,
Greg

 

[Charlie99]

Rather than beat up on either the OP or computers in general, I prefer to look at how we can better use the dive computers in recreational diving.

What I've found is that the NDLs for 50' and 60' tell me a lot. Specifically, they are indicators of the loading levels in the medium speed compartments such as 40 minute and 60 minute halftime compartments.

It's not the fast compartments that cause you to run out of air. On the first dive of the day you can go down to 120' and push right up to deco, and then very rapidly get a significant safety margin as you make a multilevel ascent and a reasonable length of stop. The 120' dive no-stop times is controlled by fast compartments. Fast to ongas, but also fast to offgas.

That 120' dive, though will also load up the medium speed compartments such as 30/40/60 minute halftimes. A 1 hour SI will only get rid of 1/2 of the loading in the 60 minute halftime compartment. So you start the next dive with a significant loading in the compartments that set the shallower NDLs like 50/60/70'. The 10 minute and even 20 minute compartments that determine NDLs for the deeper dives will have pretty well offgassed during a 1 hour SI.

Repeat this cycle 3 times and you will have progressively driven up the loading in the medium speed compartments. If you just look at the NDL for 100' or 120' you don't see this. You will if you look at 50' and 60' NDLs.

After several repetitive dives to 80+ feet, what may happen is that you approach compartment limits in both the fast and medium speed compartments simultaneously. You may have previously gone a bit past deco on a deep dive and then quickly offgassed out of deco and gotten a good margin beyond that. But if the compartments giving you trouble are the 40 or 60 minute compartments, it will take a longer time to offgas them. And unlike the 10 minute compartment, the depth of the your safety stop does significantly affect the rate of offgassing. A stop at 30' will quickly clear the 10 minute compartment, but for optimum offgassing of the 60 minute compartment you will want to be at 15' or even 10' (after spending a couple minutes at 30' and 20' to get the faster compartments a bit further away from limits).

===============================

I don't know what sort of dive logging software you have, SailNaked, but I would very much be interesting in know the NDLs for various depths at the start of your 4th dive as compared to say the start of the 1st and 2nd dives.

=====================================

Just as depth averaging deco calculations are useful, even though not technically accurate, you can also crudely estimate how fast you will use up NDL by assuming that the loading is proportional to depth. For example, if you have a reduced NDL at 60' of 30 minutes, you can estimate that after about 15 minutes at 120' you will have 0 NDL left even at 60'.

Bottom line recommendation is to be aware of the cumulative effects of repetitive diving on the medium depth (50 or 60') NDLs and how it takes a long time to offgas the compartments that control those NDLs.

 

[DevonDiver]

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[DevonDiver]

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[Jax]

Busted! I reckon I'll have to finish that "scan regression" article after all.
The elephant in the room on this one to me is PLANNING! And PLANNING ABORT CRITERIA. And DIVING the PLAN.
<snipped>

Rick

Hi, Uncle Ricky! :wavey: Oh, good, a debate point!


So, is the root cause the lack of PLANNING?

Or is it that an instructor-buddy team have become complacent of the safety tenets of diving?

It sounds like the buddy has become complacently dependent on her husband.

It sounds like the instructor became complacent about planning and safety.


So, what's the REAL takeaway? If you're a newb like me, it reinforces "Plan your dive, and dive your plan." If you have hundreds and hundreds of dives, the lesson is "Complacency gets you into trouble.

 

[MXGratefulDiver]

There are some good lessons to be learned here, without snarking about the diver or the other snarkers . . .


What this newb sees:
1. complacency - nothing wrong with the computer, it did its job - where was the diver awareness?

2. buddy communication - don't want to get your wife peeved at you . . . I'd say the wife ends at the waterline, and the buddy begins.

3. complacency . . . to take time to video your buddy

4. awareness - didn't know you were so close to going empty on your current use . .

5. planning . . . no thought of turn pressure or minimum gas

Question to you smart folks -- can't ALL that be rolled up into complacency? Should it be?

Well ... yes and no ...

1. Seemed he was aware of the situation, but misjudged the consequences.

2. You've obviously never dived with a spouse ... the effects of "relationship" often increase proportional to depth ...

3. Complacency ... probably ... but more likely an impaired judgment due to the effects of narcosis.

4. Or possibly an example of someone not believing that gas management skills are useful in recreational diving ... and discovering the consequences of that belief.

5. Yes, that and probably a result of not asking the question before the dive ... "Is this dive plan appropriate for the amount of gas I'm carrying?"

... Bob (Grateful Diver)

 

[D_B]

I have had one of those "what the hell was I thinking" moments, and I discussed it among my friends here, and my instructor .. but I would not have posted it "out there" just because I know what I did wrong, and did not want to face the inevitable "your gonna die" comments.

You can comment, and instruct those that have made mistakes, without making them feel like a fool, even if what they did was foolish ... you DO want others to post their mistakes so we, and they, can learn from them, don't you?\

[not directed at any one person, just a general comment]

 

[DandyDon]

My pony bottle is a pain in the ass, i.e. annual reg service & tank viz, break down for packing in luggage, extra luggage weight to hump around and to fly, getting in line for a fill as soon as I arrive, carrying it onto the boat, gearing up with it & testing it, dragging it thur the water, getting it back onto the boat, off the boat, in the luggage, onto the plane home, back to the house, and so forth. But when it comes in handy, it's all worth it...

 

[MXGratefulDiver]

Hi, Uncle Ricky! :wavey: Oh, good, a debate point!


So, is the root cause the lack of PLANNING?

Or is it that an instructor-buddy team have become complacent of the safety tenets of diving?

It sounds like the buddy has become complacently dependent on her husband.

It sounds like the instructor became complacent about planning and safety.


So, what's the REAL takeaway? If you're a newb like me, it reinforces "Plan your dive, and dive your plan." If you have hundreds and hundreds of dives, the lesson is "Complacency gets you into trouble.

I'm not Uncle Ricky, but I'd like a stab at answering your questions ... because it's useful fodder for discussion in THIS forum.

So, is the root cause the lack of PLANNING?

I believe so ... because establishing a planned depth and time prior to the dive allows you to establish a "baseline" while your head is clear of distractions and narcosis isn't clouding your judgment. Dive plans frequently don't survive contact with the water ... but having a baseline to compare your actual results to is often an easy way to know how close to (and what side you're on) the safe limits of both NDL and air reserves. If you're not inclined to keep those baseline numbers in your brain it's a simple matter to write them on a slate where you can refer to them during the dive. That's why we teach people to "Plan your dive and dive your plan."

Or is it that an instructor-buddy team have become complacent of the safety tenets of diving?

I think this has less to do with being an instructor than it does being on vacation, paying a lot of money to be someplace special, and wanting to squeeze every good moment you can out of it. That's something most of us tend to do when we're on a diving vacation ... and in situations like this it's very easy to become "optimistic".

It sounds like the buddy has become complacently dependent on her husband.

Having done hundreds of dives with a spouse ... and dealt with many spousal teams over the years ... I suspect it's rather the opposite ... more a case of "don't you dare tell me what to do" ...

It sounds like the instructor became complacent about planning and safety.

Most people do at some point ... and a friend of mine is fond of saying "instructors are the worst". As the saying goes, familiarity breeds contempt. If there's one take-away lesson for all of us in here, it's that we need to keep constantly vigilant to follow the rules we teach our students. Most of us who teach will at some point have a "gotchya" moment that reminds us of this ... and they often serve as terrific teaching points after the fact (assuming you're honest with yourself about why it happened) ...

... Bob (Grateful Diver)