What makes us think we can trust any of them

[Rick Inman]

Since I got bent a few months back - well within the limits of my computer - I discovered a few things my computer does not take into account:

• My age. It doesn't know if I'm 18 or 80.
  
• My physical condition. Am I 50 pounds overweight or a CA Governator?
  
• My current health. Just getting over the flu? A slight cold? Bad nights sleep or well rested?
  
• Thermal body condition. Am I diving cold or warm water. I'm I properly insulated?
  
• Hydration. How well hydrated am I? My computer doesn't have this vital information.
  
• Exertion. My computer doesn't know if I'm fighting a current. It doesn't know if I easily stepped off the boat into the water, or did a 1/2 mile hike with doubles. It doesn't know if I'm stepping back into the boat after the dive, of climbing cardiac hill.

My computers doesn't know any of this stuff, all of which can make a huge difference in getting bent or not. And either way, my computer will give me the exact same NDL!

Some computer have liberal and conservative settings. Most people pick one and leave it there even as their own conditions fluctuate.

I mistakenly thought I could do everything wrong - dehydrated, exertion, hot shower, minimum 3 min safety stop - and as long as my computer said I was OK, I'd be OK.

Until I spent a day locked in a small tube.

So, to answer the question in the thread title... I guess I don't anymore.

 

[Scuba]

After reading this article: http://www.scubadiving.com/gear/dive_computers/crunching_the_numbers/0/

I begin to understand why the DIR folks keep telling people not to dive according to their computer. The difference in remaining ndl time between the tested computers on a given profile was as great as 66 minutes. That's nuts!

I need some training on how to calculate multilevel profiles and change my computer to Guage mode.

I'm getting closer, someone pass me the coolaid! :14:

Dive computers will calculate and display your maximum No Decompression Limit based on time spent at depths. You can do the same mentally using a watch and depth gauge. Regardless of which computation method or tool you use, the result of these calculations will vary depending on the decompression model being used as a reference for determining NDL. As you noted, there is a large difference between the results produced by these various models. It should be noted that the commonly used model by DIR divers, or any other decompression model, falls within the same category. In other words, you can not look at one model, DIR commonly used model, or computer X model, and say that they are not part of the models which vary in results when compared to another model. No model stands apart from the rest as an accurate reference model.

If you are going to use your decompression model to it's maximum allowed NDL, the one with the more conservative limits, less time at depth, produces less exposure to compression. Therefore it will be safer. No compression equals no decompression issues and risks. Less is less and more is more. But there is more to it. If you compress your body you have to decompress.

NDL limits are a way to state the maximum depth and time from which you can make a direct ascent to the surface with a very low probability of DCS. This is something to do in an emergency, not in the course of a normal dive. This type of ascent exposes the body to relatively rapid decompression, which although it has a low risk of resulting in a severe case of DCS, it is much more likely to cause sub-clinical DCS symptoms such as intense tiredness or fatigue.

These NDL limits also recommend a maximum rate of ascent, such as 30 fpm and a 3 min stop at 15ft. Which brings up another point about decompression, the rate of decompression and various means to achieve it. Aside from various gases used by advanced or tech divers, it's the rate of ascent and periodic stops that encompass your ascent profile. Once you reach a level of compression, this becomes the critical factor determining how conservative, liberal, safely or not we decompress.

In addition, other factors such as water temperature, health, hydration, exertion level, amongst other factors, also have an affect on how effectively our body is able to decompress, and should be accounted for in the ascent profile.

Learn deco theory, it may seem confusing, arbitrary, and contradictory at first, yet one can apply a few simple practical rules to make diving safer. And since it is a theory, you, me, us, are all experimenting with ourselves to some degree - therefore, start conservative and progressively expand your limits in small incremental steps, as desired.

 

[Diver0001]

As for the curve that was shaped, they typically looked like the first thumbnail.
My profiles these days look more like the second one...

Looks like you spent 40 min on the wreck on the first dive and 40 minutes on teh up-line during the second dive..... :14:

I totally agree with you that you shouldn't ride the computer but, like Charlie, I fail to see how a computer forces you to do anything. If you apply "logarithmic" thinking to your ascents you'll find that your computer likes it just fine.

The issue isn`t computers, the issue is that many (most?) divers are poorly informed at best about how to perform an ascent. In other words, the issue is information, not technology.

R..

 

[Snowbear]

No, computers don't *force* anyone to do anything. But most of the divers I have observed use the computer to tell them how long they get to stay at depth and how long they have to make their ascent. All I have done here is tell folks how much better I like it and how much better I feel afterwards since I learned how to run my dives without bothering to trust a computer that turns out to not be so trustworthy after all.

I have not said that those who feel the need to rely on a computer to "keep them safe" should not continue to do so. Folks who feel that they cannot calculate their own dive profil "on the fly.... er.... swim..." should probably keep using their favorite computer to do it for them to avoid "a horrible death from the bends"

As for those profiles.... neither was a wreck dive.
The first was one of the first dives I did at Hat Island Reef in Puget Sound.

The second was a wall dive in Barkley Sound.... no upline involved

 

[Scuba]

But most of the divers I have observed use the computer to tell them how long they get to stay at depth and how long they have to make their ascent.

I have not said that those who feel the need to rely on a computer to "keep them safe" should not continue to do so. Folks who feel that they cannot calculate their own dive profil "on the fly.... er.... swim..." should probably keep using their favorite computer to do it for them to avoid "a horrible death from the bends"

For some reason the majority of divers who do not use a computer believe that those who choose to, as a matter of preference, are less able. This is probably partly explained by your first quote. Let's not forget this quote is largely applicable to new, inexperienced divers or those who have never learned any better. Misapplication of dive tables is probably just as common in divers with comparable training, only difference being the tool they use. For this type of diver I believe the computer is an improvement, naturally, better education for all, about deco theory, is the key to proper use of deco calculating tool of choice and better decompression methods.

 

[Snowbear]

Let's not forget this quote is largely applicable to new, inexperienced divers or those who have never learned any better.

Not in my experience.... unless of course you consider a diver with hundreds or even thousands of dives "new" or "inexperienced" :11:

The part about never having learned any better is likely true however

 

[Diver0001]

No, computers don't *force* anyone to do anything. But most of the divers I have observed use the computer to tell them how long they get to stay at depth and how long they have to make their ascent.

Exactly. But it's all about incorrect information

people are misinformed about the limitations of computers
people misunderstand how a computer should be used
people are mislead into thinking that the computer has their back covered
people are not properly informed about how to perform an ascent
people *are*, however, told to keep the computer in the green or to make sure the NDL doesn't get to zero.

and so on and so on an so on. I'm sure we could think of 10 more.

You know the expression "a fool with a tool is still a fool"..... well this certainly applies to how people use computers (or bottom timers) but the tool isn't at fault for that.

The information is out there but somehow it's not clearly communicated in training and sales people selling computers are frequently engaged in deliberate misinformation to make it sound like the computer is an auto-pilot.

I think you have an excellent point, which is that the computer does virtually nothing to advise you of a proper ascent. This is odd, seeing as how the manner in which you ascend is crucial to both your safety and how you feel after the dive.... However, if you know this (again, information) then you will control your ascent. The information about how to turn your ascent into a nice checkmark is out there but seldom addressed in training.

What I see in practice is taht the situation has improved dramatically. In the 1980's many people were still making ascents that would make your snorkel wobble and a safety stop was something mysterious and misunderstood. Most people didn't have a clue about the algorithm behind the tables but they used bottom timers instead of computers.... Were they safer? Some peoole would almost say "yes" because they didn't have a computer..... LOL

20-odd years later we're making much better ascents with essentially the same technology.... have bottom timers become so much "safer"? No. So what's making the difference? I'd say it's internet. Information dissemination. Best practices are being shared (for the most part) and people are learning from cyber diving what they didn't learn in their classes.

What tires me out in these discussions (this is not specifically directed at you, Snowbear, I'm just using your post for a soap-box) are the persistent comments like:

"computer users do this and that...."

or

"computers rot your brains"

or

"I dive better since I got rid of my computer"

It's all bulls*t because the issues have nothting to do with the tools. It's all about information. Properly informed divers with their brains engaged will be safe divers....irregardless of what they have on their wrist.

R..

 

[Snowbear]

What tires me out in these discussions (this is not specifically directed at you, Snowbear, I'm just using your post for a soap-box) are the persistent comments like:

OK, but.....

"computer users do this and that...."

I only commented on the diver behavior I have observed and used to do.... and like I said, it was what I observed in *most* divers who use computers.

"computers rot your brains"

I did not say that.

"I dive better since I got rid of my computer"

In my case, I dive better BECAUSE I stopped relying on my computer

Properly informed divers with their brains engaged will be safe divers....irregardless of what they have on their wrist.

Yup. But I would say they will be safer divers only as long as they actually USE the information they have gained...

 

[Diver0001]

In my case, I dive better BECAUSE I stopped relying on my computer

This was a troll....right? Ok. I'll bite.

one more time...repeat after me:

I, Snowbear, dive better because of somthing I *learned* and what I *learned* helped me to stop relying on my computer.

Yup. But I would say they will be safer divers only as long as they actually USE the information they have gained...

We certainly agree about this. Nice that we agree about something, eh?

Merry Christmas, BTW.

R..

 

[Snowbear]

This was a troll....right?

No.

one more time...repeat after me:

I, Snowbear, dive better because of somthing I *learned* and what I *learned* helped me to stop relying on my computer.

Works for me

Merry Christmas to you too!