DIR and computers

[Jonathan]

dive accident analysis the computer gives you?

Now while if you have been properly trained and are table conversant there is still so much unknown about DCS - otherwise we would not have the phase "undeserverd hits".

Being the gas guzzler that I am when diving nitrox on plopping dives I'm coming up way before the NDL because I have not got the gas.

With deco dives the dives are planned ahead, the tables are cut but used as a backup to the computer. I also carry tables on the dive. My initial tech instructor would randomly ask us our air and we had to reply within 5bar without looking at guages. Also if our computer registered .1 deeper than the planned max depth then that dive did not count towards training requirements - much easier to do that with a computer than a guage you can manually reset the needle on....

As a s/w developer my initial reaction to using computers under water was "no way - I know what happens to them!". I was and still am persuaded otherwise but that does not mean people should blindly follow them - they must know what it is doing and have a manual backup.

Just my thoughts...

Jonathan

 

[GreenDiverDown]

...is pretty cool.

But...It seems to me it only gives you part of the picture. For instance, it helps you figure your NDL while your in the water but what does it give you when you get out?

How do you get an idea of just where you are with respect to N2 loading? How does it quantify this? How do you plan your next dive? There must be more to it.

I know deco theory isn't exact but I kinda feel more comfortable knowing what pressure group I'm in...whether that's figured by a table or a computer. Am I kidding myself?

SA

 

[diverbrian]

I see what you are basing much of your premise on now. But, not all of us dive a standard mix. I dive the mix available. Sometimes that means diving a nitrox mix and then cutting it with air if nitrox is not available where I am diving. That takes away one assumption in this rule and shoots much of it out the window.

With that having happened, I am back to two choices.

1) Dive Computer
2) Tables

I did learn tables and am glad that I did. When we cover tables, that covers residual nitrogen and "common sense". In other words, by learning tables instead of simply going by computer blindly, the diver won't be doing two relatively long ninety foot dives within forty-five minutes of each other just because his/her computer "cleared" them when they were diving air and the d.c. was using a nitrox S.I. due to a software glitch. This knowledge of residual nitrogen also means that divers know why it is a bad idea to fly less than eight hours after diving even though their "dive computers" let them. This is why I would not be in support of tables going away for the recreational diver entirely.

My method: I dive the computer and use my brain to backcheck what the computer tells me. I do the same with a calculator just as they taught me in school. If I am deco diving, I dive the tables conservatively. As far as using how I feel, THAT is a blunt instrument. If I have stayed conservative enough, I shouldn't be worried about how I feel. I don't use the last couple of minutes (many times it is a wider margin than that) on either tables or computer. I descend slower than 30 ft. per minute if my dive buddy is willing to cooperate, I tend to stay at 15 ft. until I have to surface to get on the boat. It is good buoyancy practice and I actually don't like to end a dive, LOL. How I feel is many times determined more by the sea conditions (motion sickness setting in, for example), what I ate, how much sleep I got, and things like that then how much nitrogen stayed in my system.

If the deco on the fly method works for you (and it will if you care to be that disciplined about your mixes and that type of thing), all the more power to you. I just thought that I would put in my two cents. All are welcome to take it or leave it as they wish.

 

[mgri]

MHK,

Thanks for posting on the 120 rule. I was worried that I would have to carry a slate to work out the "voodoo" DIR method of diving without a computer

I WAS reading a PADI table sideways to determine multi level dives.... no more.

One quick question. Do you refer to a table with your average depth in order to determine your residual group?

Thanks again for the clarification.

 

[Simone]

Dear MHK:

I have thoughtfully read your original post. I am an intelligent person and diver, certified as PADI rescue with IANTD rebreather training. I have 153 dives since I was OW certified in July of 1998. I am a consistent, serious, recreational diver. That is, I dive as often as I can. I read the postings on this board frequently, but, as you can see, make few public responses. I am a real person; I have respect for you.

I always dive with a computer. I am perfectly capable of using tables, but why? When I dive, I make multiple dives. I prefer liveaboard diving, but my most recent dives (July) were shore-based, Grand Turk. I made 17 dives in 7 days. When I dive from a liveaboard, most recently from the Undersea Hunter, I did 4 to 5 dives a day. My computer is an efficient tool for me. I am using a Suunto Mosquito with an Oceanic Datamax Pro as a backup. I use Nitrox and I am a conservative, careful diver who loves being in the water.

I read everything on this board about DIR diving. I am convinced it is a superior training curriculum. I would not attempt the DIR-F class because I can't meet the swimming requirements. Nevertheless, based on what I have read and researched, I reconfigured my gear. On my last trip to the Turks and Caicos, I used my Oceanic Tour BC, a 5-foot hose on my primary (I am a small woman), my secondary on a necklace. I was delighted with this configuration because, for the first time, I didn't have hoses winged out on the right side of my body. I felt streamlined. I have viewed the videos I've seen on this site, and I have adjusted my descents and ascents to a horizontal position. I have tried to adopt a frog kick with bent knees instead of the flutter kick I was taught. I confess I have not been able to recreate the backwards kick I watched many times on a Scubaboard link. I understand trim and buoyancy ... I am good, but I would like to be better. For me, maintaining my position in the water column is all too often a function of the wetsuit I am wearing. I love to dive without a wetsuit, but I get cold. I have 3 mm, 5mm, and 7 mm wetsuits. If I dive in the Florida springs, which I do, or I dive in saltwater, which I also do, my wetsuit and my weighting varies. Nothing is clearcut; nothing is simple.

I dive because I love it; I want to be safe and I want to be good. I love the ocean and feel like a privileged guest in the marine world when I dive. What do you say to the people like me, MHK?

Sincerely,

Simone

 

[HammerNoMore]

Before I begin,

I'd like to state for the record that I consider myself to be a DIS diver not a DIR diver. Do some searches and read to find out the real difference but for me it means:

1) I have not had proper GUE training and
2) There are a few DIR concepts I disagree with that may or may not be covered when I do get GUE training.

It's unfortunate, but here in the most land locked city in the country, there is no GUE training. Even without GUE training I have made the slow conversion towards their styles. If you have trouble beliving this do some Google searches on my anti-DIR tirades....

Now that that is out of the way....MHK has done an excelent job of both explaining the "baker's dozen" and going beyond that and trying to explain the alternatives.

There have been some questions about repetative dives. I hope MHK stops where he is from a liabilty standpoint. It is not that he is "giving away secrets", but rather that an "internet" explanation is not enough and people who are truely interested need to take a class.....

As it is I like the computer. When I eventually get some GUE training they may or may not change my mind. Personally I'm hoping for the former. Like many of the divers on SB I'm intelligent enough that the background math does not present a problem. I beive that the GUE approach is designed to sway the "uneducated" masses away from learning to rely on electronics instead of intelligence.

As an admited "non DIR" diver", who is probaby misrepresenting the GUE standards, hopefully MHK will correct any mistakes I make. Here is what I understand:

1) Those who cannot do some simple math do not belong underwater. To this, I agreee. If your SO is "artistic" and needs an instructor to dive with them, perhaps he/she should not be dving. This may shound harsh but would you put the same person on the space shuttle? Exactly how are the environments dissimilar?

2) Every dive is a decompression dive and GUE divers plan on a "full" decompression on every dive.... As I understand it, your second, third, forth.... dive are all the same.

3) GUE does not say that DIR is for everyone. This is the most important factor. I have run my mouth far more than I should have in anti-DIR rhetoric simply because it is misnamed.

I do not now think that any real DIR diver takes the name to the extent (i.e. if you are not doing it right your must be doing it wrong.) I have wasted much time on this debate on rec.scuba and now I know better.

DeepTechScuba,

Your SO, sounds a lot like my wife. I will not give up diving with my wife to become a "DIR" diver. This is probably the biggest reason I will never be DIR. They might, and to be honest if I ever get to do DIR-F, I hope they do, convince me to give up the computer, but they will never convince me to give up my wife....

 

[nradov]

MHK once bubbled...

for example if I did 10 minutes at 100' and 10 minutes at 80, I could simply average it as a 90' dive, therefore 120 - 90 equals 30 minutes NDL..

I probably shouldn't be wasting time on scubaboard again, but I had nothing better to do tonight so here I am. Anyway. Mike, if you're going to tell people to do depth averaging to figure out minimum decompression limits for open water dives you really ought to explain that rule of thumb only works in very limited circumstances. For example, a multilevel dive to 60ft for 15 minutes and then to 100ft for 15 minutes does not average out to be an 80ft dive for 30 minutes. It's really closer to being a 100ft dive for 30 minutes in terms of the deco profile you should follow. Gas loading is not a linear function and the most recent phase of the dive has the greatest influence. I'm sure you know this and are just trying to keep the explanations simple to suit the format, but if you're going to explain deco calculations it would be better if you gave divers the real deal. It's not that much more complex.

And for those of you who seem to think the alternatives are between tables and computers, that misses the point completely. The alternatives are to either understand enough about deco to handle the dives you do, or to have no clue and roll the dice every time you get into the water. Your choice.

-Nick

 

[Albion]

"first checks he is not in technical diving section"


As i see it for recreational diving computers ARE the way to go, I think it was BigJetDriver who described those diving without computers as being in the Amish diving club.

Computers WORK and are getting more conservative, but obviously you need to know what to do in the event of a failure it can happen. Personanlly I check mine rugularly during the dive if anything starts to look like its going pear shaped then i head up slowly and chill at 5M until my air runs out. I have 400+ dives on computer and had the batteries crap out twice in that time. if you are diving recreationally then majority of the time your gas runs out before your bottom time its not an issue. Computers can do a far better job of folllwing your profile durieng a dive than you can possibly do.

 

[Custer]

MHK once bubbled...
That being said, our thinking is that many [not all], but many divers become reliant on a device that could fail.

Like a regulator, wing, mask strap, ect...

Like we can learn to compensate for the unlikely failure of this equipment, the infrequent failure of a computer (never happened to me in 6 years) isn't much of an obstacle either.

MHK once bubbled...
Would you prefer your child never learn basic math in school just because they have the ability to use a calculator??

No, but, I'd prefer they learn to type on a keyboard instead of an Underwood.

Common tables are like all those proposterous calculations you learn during nitrox class, and never, ever, ever use again.

It's a good thing to learn them, to understand the mechanics of how decisions are being made, but their use has simply been overtaken by events.

MHK once bubbled...
Thirdly, many divers are sold on the computer as a way to extend bottom times.

That's exactly what it is.

I do multi level dives on best mix, and even on-the-fly tables, while really cool (no joke) can't begin to keep up with my changes in depth on the average Adophus Busch dive.

Those tables will cost me bottom time, and bottom time is what I'm paying for.

The computer on my wrist knows exactly how deep I've gone, and how long, and isn't limited by 10 ft or 5 minute increments, like the 20/120 plan.

Plus, I gave up math homework in the 70's. I'm too busy grooving on my dive to do running math calculations in my head, especially all day.

It also shows me time-to-deco, so I can adjust my depth for max bottom time, something a table will never be able to do.

Plus an ascent alarm, and a download, two invaluable advantages.

At the end of a 6 dive day, the computer will more accurately reflect my actual dive profile than tables by an order of magnitude.

Doing one or two semi-serious square profile dives in a weekend, your plan is sufficient.

Doing 16 dives in 5 days, your plan isn't even ballpark for me.

MHK once bubbled...
That is partially true when the choice is limited to tables -v- computers. However that is only part of the equation. To the extent that the algorithm in the computer is set to a conservative gradient to provide a certain amount of "padding" more often then not you wind up with modest levels added bottom times.. For certain some models allow for the adjustement in gradient factors, but the fact is that many lack sufficient knowledge to understand the impact of the change in gradient factors.. The concept of course is that by the "padding" you reduce the very benefit they purport to give you.

This is true, too, but, given the disparity in physical fitness, dive conditions & experience, this padding may well benefit the masses.

I do truly long for either optional computer algorithms within a brand line, or a more programmable computer, and I'm sure we'll see one soon.

(We definately need a Hangover Gradient)

MHK once bubbled...
Nothwithstanding the foregoing, as diver's progress into helium based diving few in-water computers provide for gas switches, proper algorithms and are by-in-large cost prohibitive, usually in the $1,000+ range. We feel that money can be better spent elsewhere whether it be on proper equipment or training that will allow a diver to compute these calcualtions without the need for devices that can fail.

I think as a diver progresses into true technical diving, you may be right, but that's a very small percentage of the dive community.

Dive Rite 2-gas computers can be had for around $300.

MHK once bubbled...
Hopefully that more fully explains our thinking, but I remain available to answer questions

I think your explanation is excellent, and fits dive parameters that you confine yourself to, but I don't think it's utilitarian enough for my style of diving.

 

[MikeFerrara]

Albion once bubbled...
[B Computers can do a far better job of folllwing your profile durieng a dive than you can possibly do. [/B]

I think some of you are missing most of mike's point.

Every one keeps going back to the argument of precission. You are right, the computer accurately measures depth and times and then uses it to accurately calculate a model that many now believe doesn't even come close to telling us what's really going on in our body. Either way all should realize that decompression isn't that exact of a science so the precission isn't doing anything at all for you.

To illustrate my point...

Look at the DSAT, NAVY, Buhlmann and NOAA tables (others if you wish). Notice the huge spread of NDLs. At some depths you'll see as much as a 40% or more difference. Now calculate through multiple dives and look at the difference.

Take some decompression software and run the same profile several times with different gradient factors or different levels of conservatism. See the huge difference it makes?

Being a couple feet off on the depth used is insignificant compared to the differences shown by the above.

Using good dive habits like sensible profiles, good ascent technique and not pushing your dives to the limit (cuz we don't know where it is) adds all the pad you need and does more for you than precise calculations.

Average depth...

Using a decompression software, run the same dive as a multi-level dive and compare that to a single level dive using the average depth. Notice how close the results are.

One of you please explain to me how it helps to calculate with precision something that's just a shot in the dark.


Personally I don't use "120" for recreational dives because after teaching for years I have some table NDLs that I like better etched in my brain.