NDL Times

[leadweight]

In the current issue of Rodales there is a graph showing varying NDL times for several popular computers. In the profile (second dive of the day) after 35 minutes and a maximum depth of 70 feet the divers have returned to 40 feet. Computers made by Suunto, Mares (and some others) show NDL of about 9 minutes. Uwatec computers have about 22 minute NDL and Oceanic/Aeris computers have an amazing 60 minute NDL. The divers then ascend within 10 minutes and none of the computers are violated.

On a profile like this a lot of divers would have enough air left to hang around at 40 feet for 15 minutes or so. This would put some of these computers into deco. A diver with an Oceanic/Aeris would surface at 60 minutes and not be anywhere near violating his computer.

There are tons of Oceanic/Aeris computers in use, yet relativey few divers get bent. Why?

Some possibilities:

1. The more conservative computers are unnecessarily conservative by a gross amount.

2. Most divers using the less conservative computers are actually staying within the NDL's of the more conservative computers because they are low on air, cold or their divemaster wants to eat lunch.

3. Divers with greater risk factors are self selecting by purchasing the more conservative computers while mainly the young and in-shape buy the less conservative computers.

Anyone know the answer? I don't.

 

[WreckWriter]

Despite your snotty implication on number 2 you actually bring up a good point. The answer, when doing the shallow dives you reference, is number 1.

Tom

 

[leadweight]

WreckWriter once bubbled...
Despite your snotty implication on number 2...

Tom

And I suppose you have no snot.

 

[WreckWriter]

leadweight once bubbled...


And I suppose you have no snot.

Gee, I guess I should have known better than to answer a post from you. I'm really shocked that a d***o like you could even ask such an intelligent question, maybe that's why I answered. Your reply leaves no doubt that my first impression was the right one.

I won't make the same mistake again.

Tom

 

[pdoege]

I'd love to see how my Cressi stacks up.

I've been looking at the DiveRite Nitek Plus. Nice little thing.

My buddy has the Nitek Plus and we have had similar NDL results and safety stops. That being said, the general consensus is that the Nitek N2 bar goes up a bit slower and comes down faster.

I'd say, off hand, that the answer to your question is #1.

Have a great day,
Peter Doege

 

[leadweight]

WreckWriter once bubbled...


Gee, I guess I should have known better than to answer a post from you. I'm really shocked that a d***o like you could even ask such an intelligent question, maybe that's why I answered. Your reply leaves no doubt that my first impression was the right one.

I won't make the same mistake again.

Tom

The part of my post that you found to be objectionable would be viewed as dry humor by most people. You are just sore from that cave diving thread. Perhaps I am not the d***o that you think that I am.

 

[davidlkh]

I happen to own and use:
Suunto Vytec
Oceanic DataPlus
Oceanic DataTrans Plus
US Divers Matrix

After several hundred dives I have noticed:
Oceanic DataPlus
Oceanic DataTrans Plus
US Divers Matrix
Are more aggressive for NDL dives.

Suunto is more conservative for NDL dives compared to the above. BUT if I go into DECO, the above dives really really limit my subsequent dive and my deco time is very long.

Suunto seems to give me credit as I accent, so even though I am in a DECO state, as I go up it may suddenly change to no DECO. Oceanic and US Divers, will force me to go to 15 foot stop, or whatever stop is needed.

If I know at this site, it is a no DECO 2 dive day site, I will use Oceanic through out the trip. If I change my site or my style of diving, I will lay off for 36 hours before swapping to the Suunto.

So I use the computer that matches the type of diving I am going to do.

 

[Alban]

Hello
Hello ,
I have not seen the graph's you mention but some computers will account for the cold water and shorten the dive time accordingly , some other possibilities are that the ascent rate may be different the Uwatec uses a varying ascent rate , some will use a mandatory stop at 5 mts and others will use a recommended stop. They will also vary in their S.I. Times such as allowing a longer first dive but obviously penalising you on repetitive dives.

D.M's tend to dive perhaps two or even three times a day , interestingly I know some Instructors that use a computer for teaching then at the weekend where doing trimix dives using software and bottom timers , they where neglecting the build up of N2 from repetitive dives.

I think when manufactors produce a new computer it is easier to market it "safer " rather than "more aggressive" than the mainstream.

Yours Alban

 

[Dr Deco]

Dear Readers:

NDL

When looking at the different results of meters and tables following a course of diving, one can become confused. They could ask, “If these tables are taking me on edge where I am near the “bends/no bends” table limit, how can the “limits be so different? A good possibility is that there really are not any “limits.”

It is piece of false physiology that probably arose decades ago when deep tables were being fashioned. If the diver got “the bends,” the table was modified slightly and retested. Since DCS is really such a variable occurrence, increasing the deco time inevitably fixed the problem. The designers reasoned that they had exceeded a limit at some point and extending the stop fixed the problem. The idea arose that one was “walking a tightrope.”

Tables and Meters

I can imagine that deco meter designers would like you to believe that they have the ultimate decompression scheme and return you safely with the best bottom times. You will then wish to purchase their device. To this, they add convenience for the operator, easy battery replacement, download capabilities, mixed gas diving, and price. All of this is fair enough. However, the part about the best deco schedule is not demonstrable with laboratory data.

Lab Tests

The only [current] deco system with published tests is the PADI Recreational Dive Planner. It only states that it is a Doppler-tested decompression system. No claim is made that it is the best or the most optimal.

In the days when I performed laboratory testing on a contract basis, I would have loved it if all of the manufactures came for trials in the chambers. They did not. We have then many systems with [apparently] different numbers. Who to believe? They actually are all correct.

To repeat it again, more likely than not, DCS is the result of something not considered in the tables. This might be vigorous, excessive activity at depth that loads the tissue compartments in ways not considered by the algorithm. Also, vigorous activity will generate tissue micronuclei that will radically change the off gassing and possibilities for DCS.

Dr Deco :doctor:

 

[WreckWriter]

leadweight once bubbled...


The part of my post that you found to be objectionable would be viewed as dry humor by most people. You are just sore from that cave diving thread. Perhaps I am not the d***o that you think that I am.

Perhaps not.