Average or Maximum?

[SPG3K]

Well, it did click one bar up. By showing NDL remaining, what I meant, was the Nitek displays the time you have at your current depth to avoid decompression, and that number was decreasing. Honestly, the only time I've seen that number go away is when I'm at a 2min stop.

I guess the most confusing point is that at the end of the day after dive 4, I was 1 bar into the red on the residual nitrogen graph. Now, I don't see how this is possible, just estimating by my bodies' feedback.

Let's say I do a rainbow river drift dive for 2 hours, I NEVER feel tired. Let's say i go to V. Blue and do 2 15 minute dives to 110ft, I ALWAYS feel tired. Everything I've read implies that the tired feeling has a lot to do with nitrogen in the body, since obviously my physical workload would be greater overall on the 2hr in water time than 30 minute dive times. Now, if I do the safety stops, my computer's nitrogen graph is at the same spot or one higher, yet lots of the fatigue goes away. So that would mean that your body gives you a good "warning sign" if you have residual nitrogen, would it not? (If I'm wrong here, please correct me).

The only problem with that theory, scientifically is the ability to acquire any reliable sort of quantitative measurements of your "tiredness."

With any sort of measurement or "level" of anything measured by a feeling, your head can often push your "measurements" towards what you think is the answer.

Not saying your wrong, just hard to prove something like that.

 

[ucfdiver]

I do not know what algo/model your computer is running. But when you go up in a dive, you are still on gassing if you have not reached critical super saturation. (i.e you are still in NDL). Many computers for the 'safety of the user' account for this and count down NDL.

After 4 dives in the day (no knowing what they look like) it is not surprising to see res. N2 to be high. What amuses me is that you can match how you feel with a bar graph on a computer screen and disagree with that....:blinking:

Maybe I wasn't clear, I wasn't trying to match the bar with how I feel, I've just noticed that when I do the deep stops, I feel better, and the bar ends up higher, and was curious to see an answer for that.

From what I'm understanding here, the deep stops are made with the assumption that you on gas slower than you're off gassing, and the computer is raising the bar to reflect that on gassing, while ignoring the off gassing for a safety margin?

As for the dive profiles, they were basic level cave dives to 1/6 turn pressure in devils ear. 1st dive was shallower because some buddies took me through the catacombs.

Edit- it's the Buhlmann ZH-L16 algo. After reading, one of the Nitek X's new features is the ability to recognize deep stops, so I'm guessing it's implying that my DUO cannot do that.

The only problem with that theory, scientifically is the ability to acquire any reliable sort of quantitative measurements of your "tiredness."

With any sort of measurement or "level" of anything measured by a feeling, your head can often push your "measurements" towards what you think is the answer.

Not saying your wrong, just hard to prove something like that.

Agreed, I'm certainly not trying to do deco based off of fatigue. I'm sure using deeper stops after being told they're better can have a placebo effect as well, and I certainly agree with you saying to be careful of that.

 

[Meng_Tze]

The average dive computer is made to be able to get a wide variety of divers and dive profiles safely to the surface. This means that there are a lot of assumptions and yes, many do not account for the positive effects of deepstops. To those an actual deepstop simply looks like a point in a multi level dive. The computer simply is not aware of deep stops and how to account for it.

I believe that in recent years there were a few manufacturers who came out with specific 'Deep Stop' versions.

This is where reality of a profile and diver intersect with the assumed parameters of a generic implementation of a deco algorithm.

 

[Air On]

First follow your dive certification agency guidlines... (Forget the computer a moment)
It should have told you to apply your max depth to the overall duration of the dive.
This is what is meant by a FLAT dive.
If you drop to your max depth and start working your way up again gradually, the entire dive is done by the tables as if you were at the deapest point the whole time.

Dive computers on the other hand give you credit for off gassing typicaly (talk to the manufacturer of your computer to get specifics) Its not just for a shallow safety stop its a gradual sliding scale of saturation. If you don't have a manual, mst can be downloaded from online!

All dive tables from the different agencies and the Navy differ in their numbers, they are not going to match. Dive computers are in the same boat. They all run differently then other brands.
They do and tend to have a setting to make them more conservative or less for your personal needs. I think some models have an option for deep stops that basicaly adds assent alarms and depth points for you instead of only catching the final safety stop.

SAC rates and colleted data. My Suunto Cobra II has a pretty nice download program that reveals a lot more information than the dive console display allows. You do get the average total dive SAC rate but it has more settings you can turn on and get point by point data from the dive profile. It has a companion air use and water temperature graph that follow the time line of the dive profile. Even the graphic tables have more information that can be shown if you dig deeper into the settings.

I like to print them out for my dive log and then I'll rework my NAUI dive tables and compare to the backup tables I kept durring the dive trip and see how well I was tacking myself.

Looking at this, the dive computer is a LOT more forgiving and liberal with the dive off gas credits then a dive table.

As far as your SIT (surface interval time) NAUI has a portion of its table that covers this and helps plan the next dive in a series pretty well. My dive computer also has a function that allows for dive planning based on its tracking method (still need to work through that myself).

I tend to plan with my NAUI table and dive my computer at this point.

Per NAUI im encouraged to have a minimum SIT interval of an hour... the table allows less but if you wait an hour you get more time credits and drop at least a class level in gas load. Otherwise its treated like you never really got out of the water.

I noticed something though...
If your an Open water certified diver just starting out... look at the tables your dive and confirm this...

If you keep an hour surface interval to rest and refresh (Drink liquids, use restroom) You should be able to do at least 4 dives a day to a OW limited depth of 50-60 feet and not hit a deco stop. Assuming as a new diver with aluminium 80 tank and having a rough dive time of 30-45 minutes.

Do your tables... plan this as a generic dive and see if it holds true.

If your doing a dive trip you normally get a 2 tank dive each trip out anyhow. Pretty hard to blow your deco level in this instance. Hour between dives, 1 hour or 2 for meals, rides to and from dive sites...
If your on an all day trip or live aboard, you might get the 4 dives and a night dive in on one day?

Impose these boat schedules to shore dives and you should be pretty safe...
Dive, SIT 1 hour, Dive, SIT 2 hour for lunch, Dive, SIT 1 hour, Dive, SIT 2 hours for dinner.
Are you safe? Did you exceed any deco stop times?

If you take regular breaks between dives and keep hydrated, fatigue should be reduced quite a bit.

Then you need to look at if your overly animated in the water, over kicking, moving up and down in depth too many times, going deaper on later dives instead of shallower...

Just some thoughts...

 

[John_B]

First follow your dive certification agency guidlines... (Forget the computer a moment)
It should have told you to apply your max depth to the overall duration of the dive.
This is what is meant by a FLAT dive.
If you drop to your max depth and start working your way up again gradually, the entire dive is done by the tables as if you were at the deapest point the whole time.

Back before they told us to turn off our brains and just fly the computer, they actually taught multilevel dive planning.

 

[Mr Carcharodon]

There is a significant group of divers that use average depth to calculate decompression schedules. This is commonly called ratio deco or deco on the fly. The method has been used successfully for both recreational and deep decompression dives. Average depth is used in conjunction with controlled depth v. time ascent profiles. The method consists of a set of rules of thumb to mirror the decompression schedules from bubble models. Of course understanding all the details of implementing the method, and adding this to your diving incrementally would only be prudent.

There seem to be a significant number of posters who believe that it is absolutely unsafe to violate table rules and then blindly follow a computer which does just that. Perhaps those posters could explain how it is that their computers are giving them extra bottom time beyond the tables and why that extra bottom time looks so much like using the tables and average depth.

 

[SlowRain]

The average dive computer is made to be able to get a wide variety of divers and dive profiles safely to the surface. This means that there are a lot of assumptions and yes, many do not account for the positive effects of deepstops. To those an actual deepstop simply looks like a point in a multi level dive. The computer simply is not aware of deep stops and how to account for it.

I believe that in recent years there were a few manufacturers who came out with specific 'Deep Stop' versions.

This is where reality of a profile and diver intersect with the assumed parameters of a generic implementation of a deco algorithm.

Bingo!!!!

There are computers that account for deep stops, however they are higher end models usually designed for mixed gas...i.e. X1, VR3, Shearwater, etc. I have a VR3 and it does call for deep micro-bubble stops. Having said that, I never blindly put my faith only in the computer and usually check the computer's plan against tables as a sanity check. Of course they are never "exactly" the same, but usually I find what the computer calls for and what the dive tables are telling me are very similar, at least Buhlmann tables. VPM obviously is a different model and I have both in tables. In the end however, all deco algorithms are theoretical models versus hard and fast factual information.

A specific illustrative example. I did a deco dive with a group to 140 feet. We planned out the dive on V-planner using the VPM model. I wore my VR3 and the deco plan we ran bent my computer, yet we all surfaced without any issues. The plans were different, however because the VR3 called for a deep stop about 5 feet below what the VPM model called for I got the message saying "Use Tables". 2 different plans, (granted similar) that were successful. Where I start to see substantial differences is when you get into the 200' range on trimix and compare VPM against Buhlmann runtime tables.

As far as averaging depth for deco, I have seen it done successfully and have done it successfully, but it is not something I would give blindly to a person who is just getting into deeper diving. I think most people would agree that when you start down the path of deco diving and are in the learning phase of the skills, you have enough on your plate without trying to do deco on the fly. What was that saying....first learn walk, then learn fly?

 

[Meng_Tze]

....
As far as averaging depth for deco, I have seen it done successfully and have done it successfully, but it is not something I would give blindly to a person who is just getting into deeper diving. I think most people would agree that when you start down the path of deco diving and are in the learning phase of the skills, you have enough on your plate without trying to do deco on the fly. What was that saying....first learn walk, then learn fly?

Depth averaging is used in RD/DOTF, but there is FAR more to it. Just averaging depth and planning deco based on that is a valid way to run deco, especially when you are looking at longer BT. RD/DOTF has a set of basic gasses and deco commitments (i.e 1:2 for every 1 min BT you get 2min deco), has a 'set point' from where the deco commitments start, shape the ascend curve and allows for adjustments on the fly.

NB: this is a VERY simplistic overview of RD/DOTF not intended to be all encompassing.

 

[SlowRain]

Depth averaging is used in RD/DOTF, but there is FAR more to it. Just averaging depth and planning deco based on that is a valid way to run deco, especially when you are looking at longer BT. RD/DOTF has a set of basic gasses and deco commitments (i.e 1:2 for every 1 min BT you get 2min deco), has a 'set point' from where the deco commitments start, shape the ascend curve and allows for adjustments on the fly.

I understand, and agree there is much more to it than what we are covering in this discussion. Further my point was not to dispute the validity of using it during diving. My point is that there are in fact many different models out there, that potentially they all work, but they are in fact just models. Obviously there have been incidents (albeit not the norm) where divers followed a dive model exactly and still had a DCI incident. More importantly, it might be wiser to at least to start with something where you can have a written plan, such as a square profile when you are first starting deco diving. Some people take to deco with no problem...for other's it is enough of a challenge that the idea of having them not only having to deal with new skills and advanced multi-tasking is enough task loading. Maybe putting averaging in a bit later in the program. It is a matter of opinion I guess.

My point probably should be crystalized to supporting the idea that proper training and clear understanding of whatever method you choose to use for deco diving should be invested in. Let's face it, there are lots of different models for deco, even now more than one method (i.e. averaging versus deepest depth), but irregardless of what you choose, redundancy errors on the safe side.

 

[Blackwood]

The computer simply is not aware of deep stops and how to account for it.

(again: I rarely dive with a 'computer')

That doesn't make any sense to me.

Are they not merely continuously comparing a set of computed (theoretical) tissue pressures to the inspired pressure?

It would surprise me if programmers put in code to ignore any offgasing before an arbitrary depth (e.g. where someone decided a 'safety stop' should occur, or at the surface).



Since deep stops can clean out the fast tissues while still loading some of the slower ones, they could count against any model that gives equal import to all compartments and figures "NDL" based on the worst case tissue at any given moment. But that's a far cry from being unaware of deep offgassing.