Computer or Not

[Charlie99]

I do not yet have a computer. I would like to eventually get one, but being a new diver, I think it would be prudent to thoroughly learn how to use the diving tables, then graduate to a computer. The computers are a wonderful addition to any set of dive equipment, but I feel a diver should also have a good knowlege of the dive tables as a back up.

The problem is that tables don't handle multilevel dives.

I do a lot of dives that are 100' max depth, 60 minutes bottom time. They are NOT decompression dives, but instead are dives where we go down deep to look at something for 5 or 10 minutes, then ascend on up to the 70' level and look around for a while, then meander on up through 60' and 50' and finally spend 15 minutes or more at 40' or less. When tracked by a computer they are well within NDL. Calculated as a square profile dive using a table they are way off the chart.

In this sort of multilevel diving, a computer is a very useful tool.

---------------

If my dive were shallow enough that I don't approach NDL, then a computer adds very little value.

If my dive is close to a square profile, then the computer adds very little value.

If my dive will follow a profile that has already been precalculated for precalculating both decompression stops and gas consumption, then the computer adds little value.

 

[tbizzell]

What I don't understand, is with the technology available today, so many computers still penalize you for time you spend offgassing. This is my only real knock against using them. If I dive to 100ft, and I spend time on deco at 50,40,30, and 20ft, the computer should NOT be penalizing me for that. It should be intelligent enough to realize that I am taking nitrogen out of my body.

Why do I need to spend $800 on a computer that can integrate deep stops, or has RGBM to do this? Until they come down in price, I'll stick with a depth guage or a comp in guage mode, and tables..

I am just learning about decompression theory. THe assumption that by going to less depth (60 feet to 30 feet) will cause you to offgas nitrogen is not entirely accurate. The models are based upon theoretical tissue compartments that supposedly model behavior of real tissues in the body.

Each compartment has differing rates of absorption of nitrogen expressed as half lifes.
Uwatec computers have 8 of these tissue compartments. The faster compartments generally control the No decomprression time for deeper dives while the slower compartments control No decompression time for shallower depths.

While ascending to a shalllower depth will cause you to off gass nitrogen in the faster compartments, the slower comaprtments (which represent slower absorbing tissues) may still be taking on nitrogen and thus become the new controlling factor on remaining bottom time before hitting a new NDL limit.

In no decompression diving, you are not going to offgass significant amounts of nitrogen in an ascent form a deep dive to the surface except during a safety stop or in the faster tissues.

Going from 90 feet to 50 feet, will cause some tissues to stop absorbing nitrogen and may lead them to discharge nitrogen, other tissues however will still be absorbing the nitrogen.

The amount of nitrogen absorbed or offgassed also depends upon the amount of nitrogen already and your current depth. Whole books have been written upon the subject.

The assumption that going to a shallower depth will automatically lead discharge of nitrogen through out the entire body is not entirely accurate. I do not have the training, but in decompression driving, the divers will sometimes carry a pony bottle filled with a high concentration of Oxygen to be used as a decompression gas. My understanding is that high Oxygen(low nitrogen concentration) in this gas will help speed up the discharge of the nitrogen in especially the slower the tissues.

 

[Charlie99]

The rule of thumb with regards to SI that I use is: 90 minute SI = clean, < 90 SI = double safety stop on 2nd, 3rd, 4th, or 5th dive. That's not complex or difficult to remember, nor does it require a computer. In most cases we're talking a 10 minute safety stop on repetitive dives vs. a 5 minute stop, and I'm pretty sure your computer follows a similar pattern.

.................

I'm in no way saying that one way or the other is better. I'm not saying in anyway that computers will kill you because I obviously don't believe that's even remotely the case. I'm just saying there are ways to effectively plan and safely execute multiple dives over multiple days without the use of a computer, and a large part of my reason for this comes for the Tech training I've undertaken.

What is your recommendation to the original poster for planning multilevel, repetitive dives until he reaches the exalted level of tech training that you have achieved?

 

[nyprrthd]

I do not have the training, but in decompression driving......

:lol2: :lol2: :lol2: :lol2: :lol2:

I know it's a typo, but I still got a chuckle from it............. the mind reels from the possibilities!

 

[darkpup]

What is your recommendation to the original poster for planning multilevel, repetitive dives until he reaches the exalted level of tech training that you have achieved?

Ahh, the condescension is rolling off your fingers as you type.

Use depth averaging, and get better tables. For instance, the 120 rule works quite well. Take your average depth, subtract it from 120, and you have your NDL time at that depth. Example: 120 - 80' = 40 minutes.

Then again, that model has been improved upon, and some groups have combined RGBM and bubble mechanic models. Those are the tables I use, and I carry them with me in my head. If diving Air, take 100' as your base line, and give yourself 20 minutes. For every 10' increment shallower, add 5 minutes. For every 10' increment deeper, subtract 5 minutes. While on Nitrox, subtract your EAD from the depth, and recalculate.

There, I gave you two. Now what's your point?

~ Jason

 

[rjack321]

I am just learning about decompression theory. THe assumption that by going to less depth (60 feet to 30 feet) will cause you to offgas nitrogen is not entirely accurate. The models are based upon theoretical tissue compartments that supposedly model behavior of real tissues in the body.

Each compartment has differing rates of absorption of nitrogen expressed as half lifes.
Uwatec computers have 8 of these tissue compartments. The faster compartments generally control the No decomprression time for deeper dives while the slower compartments control No decompression time for shallower depths.

While ascending to a shalllower depth will cause you to off gass nitrogen in the faster compartments, the slower comaprtments (which represent slower absorbing tissues) may still be taking on nitrogen and thus become the new controlling factor on remaining bottom time before hitting a new NDL limit.

In no decompression diving, you are not going to offgass significant amounts of nitrogen in an ascent form a deep dive to the surface except during a safety stop or in the faster tissues.

Going from 90 feet to 50 feet, will cause some tissues to stop absorbing nitrogen and may lead them to discharge nitrogen, other tissues however will still be absorbing the nitrogen.

The amount of nitrogen absorbed or offgassed also depends upon the amount of nitrogen already and your current depth. Whole books have been written upon the subject.

The assumption that going to a shallower depth will automatically lead discharge of nitrogen through out the entire body is not entirely accurate. I do not have the training, but in decompression driving, the divers will sometimes carry a pony bottle filled with a high concentration of Oxygen to be used as a decompression gas. My understanding is that high Oxygen(low nitrogen concentration) in this gas will help speed up the discharge of the nitrogen in especially the slower the tissues.

You have the basics. But if you don't have the training, I suggest restraining yourself from discussing peripheral issues.

The whole issue of ascending from 60 to 30 and getting a "new" NDL is true, but not really relevant. The "new" 30 ft NDL far exceeds most gas supplies anyway.

 

[PerroneFord]

Not only that, but the ongassing of slower tissues in recreational profiles isn't a worry for me anyway. I'm pretty confident I'll be ok with my 80-100ft dives for 30-40 minutes with my half-depth deep stops all the way through 10ft and then burning up reserves in the shallows. Something tells me I'll be a lot cleaner on exit than the guy who comes up from 100ft at 30ft/minute does his 3 minute safety stop, and gets in the boat!

 

[nyprrthd]

OK Jason, now you have my curiosity aroused. I'll have to look deeper into the math you've been presenting in your posts. If for no other reason than to know how to do it. So far I've thrown a couple of scenarios at it, and it actually works! Still a lot to do if you need to adjust for conditions during a dive, but nonetheless it seems to be doable. Looking at your profile, the type of diving you do is lightyears from where I am at this point in time.

In the meantime, I'll use my computer, and look at the pretty fishes.

BTW, at no time in this thread have I felt that you were talking down to anyone (even though you are "one of those DIR guys"). But I enjoy it when someone tries to get me to use my brain. The only time that "computer" fails me is when I've consumed too many adult beverages!

 

[*Floater*]

OK Jason, now you have my curiosity aroused. I'll have to look deeper into the math you've been presenting in your posts. If for no other reason than to know how to do it. So far I've thrown a couple of scenarios at it, and it actually works! Still a lot to do if you need to adjust for conditions during a dive, but nonetheless it seems to be doable. Looking at your profile, the type of diving you do is lightyears from where I am at this point in time.

In the meantime, I'll use my computer, and look at the pretty fishes.

BTW, at no time in this thread have I felt that you were talking down to anyone (even though you are "one of those DIR guys"). But I enjoy it when someone tries to get me to use my brain. The only time that "computer" fails me is when I've consumed too many adult beverages!

A good way to get started imo is to buy or make a small wrist slate (with bungee straps) and record your depth on it every five minutes. From those numbers you should be able to gestimate the average depth fairly easily. Round things off sensibly. After your dive calculate your average depth from the recorded numbers, and then compare the result to your dive computer average assuming yours allows you to upload the dives and calculate it. Give it at least 10-20.

 

[darkpup]

Fair enough. I understand how it might be slightly more than looking at a computer screen. It does however give you a lot of flexibility that you may not realize yet.

Which brings us back to the question about computers. Does a computer simplify things? In many ways, Yes. Does it mean that a computer is a requirement? No.

It's up to the individual to make a personal choice. I believe however that with the current state of Dive Training we have today, new divers are not always presented with all of the facts on this subject.

In the end though, it doesn't really matter. You'll be safe using either method.

~ Jason

P.S. Just remember that you were the one that brought up the D word. For the record, I only recently completed my NAUI Tech course. I now have a license to learn, but am light years away from knowing.

OK Jason, now you have my curiosity aroused. I'll have to look deeper into the math you've been presenting in your posts. If for no other reason than to know how to do it. So far I've thrown a couple of scenarios at it, and it actually works! Still a lot to do if you need to adjust for conditions during a dive, but nonetheless it seems to be doable. Looking at your profile, the type of diving you do is lightyears from where I am at this point in time.

In the meantime, I'll use my computer, and look at the pretty fishes.

BTW, at no time in this thread have I felt that you were talking down to anyone (even though you are "one of those DIR guys"). But I enjoy it when someone tries to get me to use my brain. The only time that "computer" fails me is when I've consumed too many adult beverages!