Skirting the Tables

[markfm]

PF -- That's why I said I didn't think you intended it to sound that way, just that that's how it looked in print.
6 dives in a day? Ouch -- sounds more like work than fun -- gear up, dive, back up, switch tanks, SI, repeat...

 

[PerroneFord]

If my body is telling me I got bent, then I did something VERY wrong, or I had some pre-condition that was not factored into my dive plan. To make it clear, I don't think the NDL tables are conservative ENOUGH in most places. I think they are too conservative in shallow water, and too risky in deep water. Riding the edge of the NDL tables in 40 feet doesn't bother nearly as much as doing it at 100 or on repetitive dives, simply because the deco schedule is garbage. I'd MUCH rather spend 20 minutes on decompression in 20ft than 1 hour on the boat. I'll pay the extra money to dive Nitrox shallow or mix deep rather than try to work with air. It's an issue of safety to me.

Twenty years ago the bubble models were being put to the test daily. And divers were finding the edges of the model. Computers on the diver were rare, and rightly so. For some technical divers, they are still rare. Doesn't matter. If you plan the dive BEFORE you get in the water, you don't need a computer when you get IN the water.


Why is the fact that he is guessing got you and others so concerned? We all guess. To what extent is the only difference. If I go dive tomorrow, I am guessing that my physiology will come close enough to what is on my PADI NDL card that I will be safe. I am guess that my run to 120ft for 10 minutes, and my subsequent rise at 60ft per minute to 15 feet with a 3 minute safety stop, will be "safe". I could do that. Or I could do that same dive, ascend at 30ft per minute, do a 15 minute stop at 15 feet, and then burn the rest of my tank above 10 feet, and walk out much cleaner. My profile goes WAY off the NDL tables. Did I just do an unsafe dive? By the comments given in this forum, I was late getting to my stop, and I incurred a HUGE penalty for overstaying my "bottom time" by 15 minutes or more. But the question is, would I have more residual nitrogen in scenario one, or scenario two? Would I be safe to do the same dive again in an hour with scenario 1? How about scenario two?

At what point do we look at the little card and say, "I can do this more safely"?? At what point is it safe to say, this card is a great guideline to keep me safe, but there is a better way? Is it after 10 dives? Maybe at dive 5 the diver spends 2 years with Prof. Yount learning deco theory and by dive 10 he knows more about deco than anyone on SB. Making assumptions is something we do all the time both in and out of the water. Sometimes they are bad, and can hurt us. Sometime they keep us FAR safer. But a thinking diver is often a better diver, and usually a safer diver.

What if your body is telling you that you're horribly bent? It won't tell you that until it's too late. It sounds like you're just waiting for the pain and concluding after the fact that you're not bent. Unless you meant something else by this I'm going to get all worried about you.


20 years ago almost nobody was diving with computers and the ones that were available got neat little nick-names like "bend-o-matic". Tables worked 20 years ago and they still work. Computers make them less relevant for puddlestomping than they used to be but that's about it.


"quite possible" .... "maybe" .... it's the very fact that he's guessing that has people concerned. Guessing isn't the way to plan dives. There are better ways to extend your exposure safely. Don't you think?

R..

 

[jonnythan]

Peronne, this guy was flat out asking an internet forum if it's OK to bend the tables. He doesn't have 2 years of deco theory, he wasn't "thinking" when he did it. I bet he will in the future, but you can't possibly advocate breaking the tables "just a little bit" because "it probably won't hurt."

Breaking the only rules that you know because they're too inconvenient for you has no possible defense. Going outside of the only rules you've ever even been exposed to isn't evidence of a thinking diver, it's evidence of an unthinking diver. A thinking diver would go out and LEARN some deco theory, not guess.

 

[NSDiver]

Peronne, this guy was flat out asking an internet forum if it's OK to bend the tables. He doesn't have 2 years of deco theory, he wasn't "thinking" when he did it. I bet he will in the future, but you can't possibly advocate breaking the tables "just a little bit" because "it probably won't hurt."

Breaking the only rules that you know because they're too inconvenient for you has no possible defense. Going outside of the only rules you've ever even been exposed to isn't evidence of a thinking diver, it's evidence of an unthinking diver. A thinking diver would go out and LEARN some deco theory, not guess.

To be fair, my original question about bending the tables was rheotorical. I haven't tried to defend my decision to break the tables in this thread - I've merely explained why I made it, and why it was a mistake (perhaps SB could use a "lessons learned" forum). When I did my certification, I never really thought about a scenario when I might break the tables. After the dive, I had a different perspective, so I brought it up here, and I thought (I suppose correctly, based on 80+ responses) that I'd see varying viewpoints on what I did. I think a lot of us newbies can learn alot from what some of you have said.

I have studied some decompression theory - but I'm not claiming to be an expert. I know enough that I could reason to myself that:

1. The tables are designed for square profiles at maximum indicated depth - they theoretically calculate how much nitrogen a person tissues will absorb at that depth for a certain duration, and give a NDL limit for that depth.
2. I didn't dive anywhere near a square profile (as I'd assume is rare). Because I spent the majority of my time at depths less than 45 feet, and a significant portion at 30 feet, my tissues would absorb less nitrogen than indicated by a square profile at a depth of 50 feet. So, the seconds spent at 52 feet would be more than compensated for by the time spent at shallower depths.

So, I rationalized. Because doing what I did was technically outside my training, it was wrong. If I had happened to stay for a greater length of time at that depth, or perhaps visited a deeper depth, would I have switched to my plan for a 60' dive? Absolutely. But that calls into question, "how much deeper?" and "how much longer?" That grey area is what can cause divers to get into trouble - and the more a diver explores the grey area, the more likely it is to bite him. A little knowledge could be a dangerous thing if not well applied.

In PFs defense, I don't think he is advocating what I did (read earlier posts). He is merely saying that he'd rather see someone think through a problem than blindly follow rules about a theoretical model such as the recreational dive tables. I do believe I thought through this problem - though I ultimately came up with the wrong conclusion, which is maybe why I've been labeled as 'unthinking.' I went beyond my training at an extremely early time in my dive career, which is a mistake. I wouldn't like to get into this habit (so I won't).

I hope I didn't open up any new cans o' worms in this post...

 

[JustinW]

Its about time some other reasonable people have joined this thread. It is deeply troubling just how easily some divers will tell this newbie to go ahead and push the limits, round down on dive profiles and what not. Thank you Jonnythan and Mark for some sensibility around here.

 

[TheRedHead]

In PFs defense, I don't think he is advocating what I did (read earlier posts). He is merely saying that he'd rather see someone think through a problem than blindly follow rules about a theoretical model such as the recreational dive tables. I do believe I thought through this problem - though I ultimately came up with the wrong conclusion, which is maybe why I've been labeled as 'unthinking.' I went beyond my training at an extremely early time in my dive career, which is a mistake. I wouldn't like to get into this habit (so I won't).

I hope I didn't open up any new cans o' worms in this post...

I also agree with PF and it is apparent that you have indeed thought this problem through and for that I think you deserve a Get Out of Jail Free card. PF may not agree with this advice: Get a computer to extend your bottom time. You would have known exactly where you stood as far as nitrogen loading and NDL minutes. You are truly limiting yourself with tables. There are many shops in places like Cozumel that won't let you dive without a computer. With 120 cf of Nitrox and a Coz fast 6-pack, you can make some interesting - and long - dives within your MOD and the computer is a valuable tool in executing those dives safely.

 

[Sideband]

But that calls into question, "how much deeper?" and "how much longer?" That grey area is what can cause divers to get into trouble - and the more a diver explores the grey area, the more likely it is to bite him.

But it isn't a grey area. There are tried and true ways of working multilevel dive profiles. Not knowing how to do it does not make it a grey area.

Joe

 

[Diver0001]

In PFs defense, I don't think he is advocating what I did (read earlier posts). He is merely saying that he'd rather see someone think through a problem than blindly follow rules about a theoretical model such as the recreational dive tables. I do believe I thought through this problem - though I ultimately came up with the wrong conclusion, which is maybe why I've been labeled as 'unthinking.' I went beyond my training at an extremely early time in my dive career, which is a mistake. I wouldn't like to get into this habit (so I won't).

I hope I didn't open up any new cans o' worms in this post...

I don't think you've opened up any cans of worms. You've done something that a lot of people have done but you had the guts to put it up for scrutiny.

As for PF, on the surface he's saying think it through but based on what he's said so far it's coming across as "double guessing" the experts. He appears to be convinced that he knows enough about decompression theory to work out his decompression needs on the fly based on what I'm receiving as gut feeling. There's proably more to what he's doing than just that (I sure hope so) but I would caution you against adopting these practices (including the thing you did) unless you have a deep and intimate understanding of decompression theory.

R..

 

[PerroneFord]

Diver0001, I am NO WAY trying to suggest that I, or the poster know enough about deco theory to do "on-the-fly" deco. Doing that correctly takes training and quite a bit of study and practice.

All I am saying is that certain other tables that I, and apparently the original poster, are are of, would have properly credited him for what he did. However, if he wasn't diving to those tables, and merely used what he "thought" as an excuse to bend the rules a bit, he was wrong. And he has admitted he was wrong,and everyone here, including me, has said as much.

Redhatmama, what makes you think I wouldn't agree that he should get a computer and extend his time? Thousands of divers do this every year and stay quite safe. It's a marvelous alternative to guessing! If I didn't calculate all my dives as square profiles, I'd probably be right there using one, because for multi-level dives they are terrific.

 

[Diver0001]

All I am saying is that certain other tables that I, and apparently the original poster, are are of, would have properly credited him for what he did. However, if he wasn't diving to those tables, and merely used what he "thought" as an excuse to bend the rules a bit, he was wrong. And he has admitted he was wrong,and everyone here, including me, has said as much.

I see. That's a bit like saying " if my other car were a Ferrari it would go faster... "

But at least I'm following what you're on about now and I'm less worried about you :05:

R..