Info Why are tables not taught in OW classes anymore?

[dmaziuk]

However if you were to pre-plan that same dive in a real computer, and dive the plan, then you'd be diving with established guidance and thus be just fine.

 

[Eric Sedletzky]

Well, guilty as charged.
This was a very typical dive we used to do off a wall outside of the keyhole at Vandamme in Mendocino Co.
I used to do this dive on tables way back. Then I got a computer (Suunto Vyper of all things lol!) and one day did the dive with the Suunto and also decided to log the times it gave me on a slate as I ascended to higher depths, pretty much the profile I posted.
Back in the parking lot I sat down with the tables and did some math and this is what I pretty much saw. The only difference is the table figures everything from the initial descent, the bottom time spent at 90’, then my own safety calculation of treating the rise from 90 to 60 as time all still spent at 90. The computer will measure every increment of every second of different depths so time spent at 90 to the computer would be less.
So you might say I used the computer as a learning tool to actually see what the upgraded dive profile should look like, not just a square profile. In this case the computer taught me, not the tables like everybody thinks they should to computer users.

 

[L13]

The problem is that your system is untested and unverified by any research. It might produce a safe dive, as it did in this case. It might not. Right now the only way to confirm it is to compare it with a computer, as scubadada did.

If it can be shown to be consistently more conservative than a particular algorithm, then it is just as tested as that algorithm.

If I can prove:
NDL method <= NDL tested algorithm for all dive profiles valid with method

Then:
all testing and verification of tested algorithm as safe validates method as safe.

I think it has been fairly well shown that many of the "table methods" will be consistently more conservative than ZHL-16C GFhigh=85% as long as the multilevel dives are constrained to monotonically decreasing depth after the initial decent.

 

[Eric Sedletzky]

However if you were to pre-plan that same dive in a real computer, and dive the plan, then you'd be diving with established guidance and thus be just fine.

So, in other words because the dive was figured on tables (illegally) but works, it’s questionable, but it’s just fine if it was done using a computer??
It’s the same dive!

 

[dmaziuk]

So, in other words because the dive was figured on tables (illegally) but works, it’s questionable, but it’s just fine if it was done using a computer??
It’s the same dive!

Well, actually, in one case you're getting in the water with a known(*) calculated probability of DCS and in the other: no.

Similarly, if your profile "can be shown to be consistently more conservative than a particular algorithm", then it is still a "no".

*) Known to somebody, like: people who designed the algorithm.

 

[Eric Sedletzky]

The problem is that your system is untested and unverified by any research. It might produce a safe dive, as it did in this case. It might not. Right now the only way to confirm it is to compare it with a computer, as scubadada did. The only thing we know based on research is that the table guidance was over one minute before you left the 60 foot level. After that, you were diving without any established guidance.

We were diving without any documented guidance only in the aspect of slowing down our ascents to take in more scenery. We were not doing sawtooth profiles, we were not depth averaging, and we were not violating initial deep NDL’s, just fudging ascent rates a little figuring percentage of BT used and applied to the next level, a very crude example of what a computer does. As I remember the rules for tables are the dive starts from the time you drop under the waves and begin your descent to the time you are done at your deepest depth and begin your ascent. There is no hard rule on how long it takes you to get to the surface as long as you do not stop or exceed the speed of your smallest bubbles or 60’ per minute (now 30’ per minute).
I’m not saying it’s right that we got hung up and made it a multi level dive, I’m just saying we did it and when compared to a computer algorithm later it turns out it worked and we were within spec.
You have to realize the times too, not everybody had computers and tables were still taught, GUE was not around on the west coast yet so their anti-computer/ratio deco was not a thing yet.
Yes we went out in a limb and did our own thing based on a hypothesis, so shoot me!
And, scubaboard was not around and it’s table police wasn’t a thing yet either, so…

 

[L13]

Well, actually, in one case you're getting in the water with a known(*) calculated probability of DCS and in the other: no.

Similarly, if your profile "can be shown to be consistently more conservative than a particular algorithm", then it is still a "no".

*) Known to somebody, like: people who designed the algorithm.

DCS risk is usually expressed as "DCS risk < X% chance of DCS".

If A < B, and B < C ==> A < C (basic logic)

1) DCS risk of ZHL-16C GFhigh 85% < X%.
2) DCS risk of "method" < DCS risk of ZHL-16C GFhigh 85% ("method" always produces shorter NDLs)
==>
3) DCS risk of "method" < X%

No further testing and validation is necessary to assert 3) if 1) and 2) are true.

This is exactly the same logic used for the standard method of using dive tables where you use max depth and total bottom time and treat them as a square profile on the table. The "actual" dive profile isn't square, and wasn't tested and validated, But, we know the risk of a non-square profile is bounded by the risk of the square profile (assuming additional rules are followed, like "no saw tooth profiles", etc.).

 

[scubadada]

Neither my ancient Oceanic VT3 or my modern Shearwater Teric allow me to plan a multilevel no stop dive. I'm not going to plan in MultiDeco, though that could work. In addition, I really never know my depths, time at depths, etc.

Just use a dive computer or 2 for your dive. A long thread with an easy answer for modern diving

 

[Eric Sedletzky]

Neither my ancient Oceanic VT3 or my modern Shearwater Teric allow me to plan a multilevel no stop dive. I'm not going to plan in MultiDeco, though that could work. In addition, I really never know my depths, time at depths, etc.

Just use a dive computer or 2 for your dive. A long thread with an easy answer for modern diving

Well sure, that’s how I’d do it now, but that was then and that’s what we did.
BTW, I’ve never been bent and I’ve never been dead, so here I am.

 

[scubadada]

Well sure, that’s how I’d do it now, but that was then and that’s what we did.
BTW, I’ve never been bent and I’ve never been dead, so here I am.

I have over 2200 dives on DSAT, I've never been bent either