NDL

[Diver0001]

I'm going to throw a wrench in the works here and take the devil's advocate post..... Don't take it personally but there's another side to the argument that gets overlooked, IMO.

MikeFerrara once bubbled...
<snip>

I'll try to get to the point. Many divers do what I call ride the computer. If the computer says they have bottom time left and they have gas all is well. Often these divers will ascend when they see their NDL getting very small. They later move up again when the see it getting small again. When they run low on gas they ascend maybe doing a short safety stop on the way out of the water.

So what? Many divers aren't interested in becoming "divers" the way many regulars of the scuba forums are - skilled, independent, self-reliant, knowledgeable and so on.

Many divers want to go on underwater horse-back rides on their vacations and they're perfectly happy (stress this point) having someone else hold the reins. Many divers just need a count down to zero, an ascent indicator and free access to the surface so they can do what they learned and a DM can show them the way. And let's not forget the fancy log book to write it all down in. In other words, many (if not most) recreational divers are quite happy to " ride the computer " and what not? *They* are not the problem. *We* are. They are blissfully ignorant and making countless millions of virtually incident free dives each year fueling the dive industry while we get all indignant about the fact that they can't execute a deco-dive. Good Lord!

If puddlestomping (this is what I call this kind of diving) is what people want then show them the risks and issues and show them how to deal with that. Train them to be safe in the few things that they learned. Teach them not to push their boundaries without supervision. I don't see the problem here. I mean, who cares if they're not really maximizing their bottom time? Who cares if they can't dive the Andrea Doria? They don't seem to care; why in hell should anyone else? It's not *our* problem. In fact it's not a problem at all as long as trainers take a " safety first " attitude.

PADI (et al) never set out to create good divers. They set out to create reasonably safe divers within certain well defined boundaries. You don't want most divers encurring any kind of overhead, even (expecially?) deco. What UP said is true but it has to fit in this context too.

Ok, so some divers will want to go further. Single them out. Let the rest play follow-the-leader behind a DM and have fun in their own way. Who are we to get all arrogant and judge whether or not their fun is good enough?

I mean, what is the earth-shaking issue here? I just don't get it.

<snip>

Avoiding the NDL isn't the objective.

Yes, of course it is! Puddlestompers need free access to the surface. Period! That's a major safety issue. The fact that the underlying reason for the NDL's being set like they are is to avoid " bad bubbling " is secondary to the category of divers in question. They just really don't (most of them) give a rat's-ass why it's like that. They're just looking for some not too complicated good old fashioned fun. When things get pear-shaped and aren't having fun any more they need to be able to abort.

The objective is to surface with minimum (bad) bubbling. In this sense there is no such thing as an NDL and if there is we really don't care. Limiting time at depth is only one small part of what we're after.

Once again. The NDL represents free access to the surface. This is a major safety issue for " many " divers and shouldn't be dismissed out of hand.

BTW, I sent a get well e-mail today to a guy who, last I heard, was still walking with a cane a month after a dive where he stayed within the limits of his computer.

Ok. This can happen. I don't know what you're trying to say here. Do you seriously want to suggest that if they had been trained differently it wouldn't have happened? I doubt you can assert that with absolute certainty. Maybe if it was a " deco " dive it would have been even worse. Who knows?

So. There's my 2c worth from the devil's advocate's point of view. Fire away.

R..

 

[ERP]

Diver0001,

I think your missing the entire point. IIt isn't that riding the NDL is bad in and of itself, it's that riding the NDL with no understanding that your computer is really justy accounting for time and depth underwater and that there is more to it than that. Riding the NDL dive after dive is just not very smart.

Having said that, the number of people who get an "undeserved" hit is very small.

 

[jonnythan]

JeffAustin once bubbled...
I dive a Vytec, in gauge mode.

Why on earth would you have a brand spankin new top of the line mutli-gas deco computer.....

for gauge mode?

 

[JeffAustin]

jonnythan once bubbled...


Why on earth would you have a brand spankin new top of the line mutli-gas deco computer.....

for gauge mode?

1. Big numbers, minutes and seconds in the middle, resetable for
deco. Total runtime in lower rt. corner.
2. Tank pressure in lower lt. corner of screen.
3. Logging capabilities, including profile graphs.

It is easy to read, I like that most.

 

[wreckchick]

I agree but didn't have the cojones to say so.

I'd like to take your idea one step further.... what about the diver that knows he/she shouldn't rush into technical diving and wants to dive for experience and fun? There is no way to build experience than by diving, diving a lot, and paying attention to what happens on a dive.

I get frustrated by the technical divers on this forum trying to make rec divers abide by tec standards. The only thing these two objectives have in common is a tank on the back and even that is up for interpretation.

A frequent contributor to this board is, by many opinions, rushing into the more technical aspects of diving. Many recreational divers may be rec divers today and tec divers tomorrow, but how else do you suggest that the rec diver gain the necessary skills to progress without using the tools available to them at the rec level?

I hear a lot about "dive more, dive within your training, don't rush into anything, get more training" but rarely does the diver who is poking along getting more dives under their belt get a break for doing things nice and slow. They are more often rushed into more advanced training then bashed for taking a class they aren't ready for, the instructor is bashed for letting a diver with that kind of experience do those dives. Then everyone blames PADI. Guess what? LOTS of people on this board are just as guilty of rushing a new diver into more advanced training as any PADI rep.

The flame retardant undies are in place. Enjoy!

Rachel

 

[The Chairman]

I think you guys are onto something. In fact... let me extend your thought processes a tad bit further. Not only are we (as a board) "pushing" recreational divers into technical mode way too quickly, but we are even advocating a certain snobbery as we do it. It has yet to be said, but if you read between the lines of some posts you can almost see... "if'n you don't dive jest like me, then you are sech a complete fool, that it ain't funny!"

NDLs were developed first by the Navy and resulted in very few incidents. The agencies have made these safe tables even safer. Making it near impossible to develop DCS if you stay within them. They actually have far more testing facilities and data than all of us combined to corroborate their NDLs.

But it does make one sound "safer" to dis these limits. Wiser even. "Heck, you think they are safe, well what about me? I don't use no stinkin' NDLs!" Then we make getting DCS sound like the unforgiveable sin. No wonder that DAN reported that there is a HUGE lag time between the occurance of DCS and getting a diver to the chamber. We are too ashamed to admit we got "hit". Or we "filter" the data a bit and claim it was an "undeserved hit".

Limits is limits! Don't push them, and please, please don't exceed them. Use them in planning your dives... thats what they are there for! They are not the cliff... they are the FENCE around the cliff with all sorts of flashing lights and reflective tape so you don't go over the edge.

AND... if you use a computer, you can relax a bit. If your dive takes you into unforseen circumstances, then it will be able to moniter your profile just fine as you attend to more important matters. Those who dis them sound like a lot of my customers when I am trying to persuade them to go with a domain server. "But what if the server crashes?" Use this protocol and you won't die. "But, what if we forget to backup at night?" Then use this other protocol and you still won't die. They are sooooo beyond being rational with their "techno-phobia" that I have no response to them. You just can't argue irrationality, so I won't even try!

One last thing... I see many divers on the boat or at the springs that are not using a computer to dive with. The sad part is, that they don't even have a table with them either. Thats right... divers who don't have a computer are usually too stinkin' lazy to use their tables. So what is safer? Diving with no guide, or with a computer?

And I can't believe that I am hitting the send button... :tease:

 

[Zagnut]

If you stay down any longer at all than tables allow, you are riding your computer to some extent...and depending on your risk factors for DCS (weight, dehydration, water temp, or whatever)even diving within the tables means your still running toward the edge of a cliff with a blindfold on, your just a lot farther from the edge. It's a risk vs. reward thing like O-ring said. I liked MikeS's speedometer analogy. Your computer may be giving you the info, but you are the one who decides what you are going to do about it.

If I'm diving locally, I usually try to use the last half of my tank for a really slow ascent( if I'm diving in a lake and not a 40' deep quarry). It may take me 20 to 30 minutes or so to get from 90' to 15'. I mean I'm poking around and checking stuff out and all, I just try to meander my way back to shallower water, so it's not really a full fledged ascent like you think of when you say ascent. I might overstep the tables but I stay well within the NDL limit on my computer because my profile is not a square profile and the last 20 minutes or so is usually in about 50' or less ending up at my safety stop. It seems like many of the guided bluewater dives I have done, have had roughly the same profile

As far as the Carribean divers are concerned, they aren't necessarily diving without a plan. "level off at 80' and drift for 30 minutes or 700 psi, whichever comes first" may not be an elaborate plan...but it IS a plan. Now the guy who keeps wandering off, sawtoothing, getting mixed up with other groups or whatever is without a plan, but if the divers pay attention to the pre-dive breifing, they should have a plan, albeit a simple one.

 

[Zagnut]

..about divers w/o computers or tables. I've seen folks on a diveboat without either...and now that you mention it, unless they remember their tables well enough to know whether or not the DM's plan is within their NDLs, then they are in fact diving without a plan and are just playing follow the leader.

I use a Genesis REact computer and wear a watch with a max depth guage and the dive tables printed on the wristband, so if something happens to my computer underwater and I'm still within the table's NDLs I can continue the dive on tables. If I'm out of the table's NDLs when my computer screws up, I would just abort the dive.

 

[KentCe]

So the point of this thread is that divers should have a good understanding of "current" decompression theory. Cool, I agree.

There are numerous sources of information and training available on the subject (for those divers that care). So whats the problem?

I would be more happy if some divers didn't smoke a pack (or more) a day on a dive trip and maybe hit the gym now and then.

 

[sheck33]

biscuit7 once bubbled...
I trust my brain to know if my computer is acting completely out of line, but I trust the calculations in the computer better than I do the ones in my head, on the fly. Having a computer doesn't give anyone an excuse for not having a plan. No one seems to think that using the tables and doing hand calculations is using a crutch when a computer is. The computer is a faster, more efficient set of tables.

Honestly, why would I want to wean myself from the computer? Why couldn't I use it forever and ever? It's not a sign of weakness to use the most efficient tool for the job. I don't see people still using an abacus because a calculator is some new fangled thang not to be trusted!

R

interesting. To stick with the calculator analogy. Just as with divecomputers, a computer really is only as smart as its user. Undergrads here at the UW tend to use calculators without thinking about the numbers the calculator produces. That leads to some interesting results sometimes. So while a divecomputer can do calculations much faster than a person they still are, dumb, yet fast, calculators, no more, no less. Of course one additional problem is the ridiculous level of conservatism built in by manufacturers, that is merely a liability issue. So i think computers should most certainly not be blindly trusted.

Also getting bent or not depends on more factors than whether a NDL was exceeded or not. Lets make sure that in addition to using computers or tables we turn on the brain.