Info Why are tables not taught in OW classes anymore?

[L13]

Yes. Exactly. Herr Doktor Buhlmann has tested and verified ZH-L16 at GF High 85% and found the risk to be below X percent. Of something. Therefore no further anything is necessary.

Actually, Buhlmann never tested anything with GF's, That is Baker's idea.

 

[dmaziuk]

Invisible sarcasm tags strike again!

 

[Eric Sedletzky]

As I have said many, many times over the years, once you begin an ascent within NDLs, you can generally take your sweet time on that ascent, as long as you don't dilly dally long enough to go into deco. In many and perhaps most cases you will be just fine. The problem is you are winging it the whole time, and you won't know when you have crossed the line.

That’s true.
But taking a computer to the max and milking it for everything it’s worth to the last drop of NDL on every dive day after day is winging it too IMO. Even though it’s a “computer” and infinitely smarter than any human could ever be, there are factors beyond any algorithm that affect the human factor, age, fitness level, tiredness, gas loading, offgassing, etc.
Just because a computer says you can do a dive and be fine doesn’t always mean that’s true, and nothing is foolproof.
In some ways it can be worse, blind faith in the savior and the new answer to everyone’s life. Computers are still just a very general tool, a complex one, but none the less a mechanical tool that is NOT directly hooked up to your bloodstream or your physiology to give you an exact readout if what’s happening to YOU right at that second in real time.
I get a chuckle when I hear people talk about their computers like they are a living thing, lol!
“My computer said I can’t do this or that”, or “it didn’t like this and put me into mild deco” (when you know it’s BS), “it locked me out” (put you in time out), whatever. Like it’s become some sort of overlord that everyone is to obey now because they don’t have a brain anymore.

Then all the different algorithms, some of them proprietary, why are they all different and who is right?

 

[Joneill]

That’s true.
But taking a computer to the max and milking it for everything it’s worth to the last drop of NDL on every dive day after day is winging it too IMO. Even though it’s a “computer” and infinitely smarter than any human could ever be, there are factors beyond any algorithm that affect the human factor, age, fitness level, tiredness, gas loading, offgassing, etc.
Just because a computer says you can do a dive and be fine doesn’t always mean that’s true, and nothing is foolproof.
In some ways it can be worse, blind faith in the savior and the new answer to everyone’s life. Computers are still just a very general tool, a complex one, but none the less a mechanical tool that is NOT directly hooked up to your bloodstream or your physiology to give you an exact readout if what’s happening to YOU right at that second in real time.
I get a chuckle when I hear people talk about their computers like they are a living thing, lol!
“My computer said I can’t do this or that”, or “it didn’t like this and put me into mild deco” (when you know it’s BS), “it locked me out” (put you in time out), whatever. Like it’s become some sort of overlord that everyone is to obey now because they don’t have a brain anymore.

Then all the different algorithms, some of them proprietary, why are they all different and who is right?

Who is "taking their computer to the max and milking it for everything it’s worth to the last drop of NDL on every dive day after day"? No one that I know does that nor have I seen that approach supported here!

 

[boulderjohn]

Who is "taking their computer to the max and milking it for everything it’s worth to the last drop of NDL on every dive day after day"? No one that I know does that nor have I seen that approach supported here!

It's called a "straw man." When you need an enemy you can harm without fear of retaliation, sometimes you just have to create it yourself.

 

[Blackcrusader]

Who is "taking their computer to the max and milking it for everything it’s worth to the last drop of NDL on every dive day after day"? No one that I know does that nor have I seen that approach supported here!

Certainly not me. When I do my dive vacations of 2 weeks then generally do 35 - 40 dives. When I do dives that are say from 30m - 40m
( and beyond at times ) the only time I really get to 1 min NDL time is on those deep dives. Generally other dives not getting close to NDL maybe 15 mins to NDL on dives of 25m depth or less.

Occasionally I do like to do a dive to a more square profile, like staying at 25m till say 2 min NDL then ascending to 15m and hanging around to say 5 minutes NDL which on my Perdix using GFhi 95% is around 55 mins. Also very few recreational divers with Shearwaters and DM's often use Suunto and have far less NDL time on dives than I do on repetitive dives over 12 straight diving days. My last dive trip 32 dives 38 hours of dive time.

Had a good beer day off with my DM guide after the previous nights pig fest on my last day of diving. Me off gassing before flying next day my DM off gassing from tagging with me for 12 days lol All on 21%

 

[Eric Sedletzky]

Who is "taking their computer to the max and milking it for everything it’s worth to the last drop of NDL on every dive day after day"? No one that I know does that nor have I seen that approach supported here!

The point is, it can be done, and according to whatever computer you’re using you could avoid deco and still be OK, which in reality may not be the case. People have gotten bent doing a lot less.
And yes I’ve known several people who used to brag about about such practices over the years, in person not here. I don’t think anyone here would admit to doing it.

 

[rx7diver]

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.).

I dive tables, only. (No PDC.) Recreational profiles, only. And my approach is as you describe: Treat run time as bottom time. (So, be back at the surface before you hit NDL.) If possible, dive to depth, and then work your way up. Surface interval doesn't begin until you're out of the water and out of your kit. Generous surface interval. This is how I was taught, and how I have always done recreational dives.

And seldom more than two dives a day. But this has more to do with the distance (3.5 to 4.5 hours, half a day's drive) to my preferred local dive spots: Drive down Saturday morning. Do two dives. Wake up next morning, and do two dives. Drive back Sunday afternoon. Arrive in plenty of time to clean gear. Perfect.

rx7diver

 

[Scott G. Bonser]

Many new divers have been trained only to use dive computers; they have had no introduction to or any familiarity with dive tables.

Many posts on ScubaBoard respond to posts about “what do I do if my computer fails” with the statement, “just use tables.”

This is a disconnect….

Here is the deal on tables, why they have pretty much disappeared from recreational diving, and why the idea of tables (and sometimes their use) is still valid.

Both dive tables and dive computers try and estimate the amount of nitrogen you have absorbed into your body as a result of the amount of time you have spent at depth (i.e., under pressure). It is the (greater than atmospheric) ambient pressure at depth that pushes the nitrogen into your tissues and blood, and with more time spent at that depth, more nitrogen gets pushed in.

The models that try and track this “on-gassed’ nitrogen are mathematically messy. Most of them assume that your body is composed of a number of different tissue types, co-called “compartments,” some of which absorb the nitrogen more quickly, others more slowly; and, each of these compartments has a maximum amount of nitrogen it can absorb. There is a lot to keep track of. While you are underwater at some depth breathing compressed gas, your body is absorbing all this nitrogen, and then when you ascend the nitrogen begins to “off-gas,” which it can only do at the same rate at which it on-gassed, which of course is a different rate for each of the assumed compartments!

When the dive tables were first developed, there were no electronic computers like we have today. Everything was done by hand using mechanical calculators and pencil and paper. Consequently, the table-makers wanted to keep it as simple as possible, so the tables were for “square profile” dives, meaning you descended to a depth, stayed at that depth for the duration of the dive, and ascended. That was OK at the time, because there were no real recreational divers swimming up and down and around coral heads looking at pretty fish and investigating wrecks, and working dives (Navy and commercial) tended to actually be square profiles; everything was fine with tables.

The down-side for square profiles was that the amount of gas used was based on being at the maximum depth for the entire dive, until you ascended, so it was common to run out of gas before hitting your No Decompression Limits. This was also fine, because there was less worry about the “accuracy” of the NDL calculations.

Those early dive tables (for example, the US Navy dive tables) had another assumption built-in that was rather restrictive for recreational divers; the slowest compartment (the one that “controlled” your on-gassing buildup of nitrogen, and your off-gassing rate) was deemed to have a time-constant of 120 minutes. This meant that the surface interval between dives when you were doing a multi-dive day had to be rather long….or you were not doing much off-gassing.

Diving Science And Technology (DSAT), a corporate affiliate of PADI -- starting in the mid-1980s -- rethought recreational dive tables based on using a 60-minute compartment (instead of 120 minutes) as the controlling compartment; using other modern technologies (like Doppler bubble sensing and electronic computers) they developed the Recreational Dive Planner (RDP), which allowed for shorter surface intervals and more granularity in the on- and off-gassing calculations. That model – originally available only in standard dive tables – also became embedded in an electronic hand-calculator version of the table, in an analog circular slide-rule version (The Wheel), and finally in several dive computers, where it is known as the DSAT algorithm.

The big advantages of DSAT and the RDP model over previous models were that (1) it was specifically for non-deco diving, so did not need to have embedded in it any additional conservatism for decompression diving, and (2) since the controlling compartment was only 60 mins, surface intervals could be shorter and thus single-day repetitive diving was made more realistic and easier.

The huge advantage of having the gas on-gassing and off-gassing tracked by a computer that you work on your wrist (or had in a console) was that you could track your actual dive, with its ups and downs, and not be forced into a square-profile assumption. As a consequence, instead of going to (say) 80 feet and spending your entire dive there, you could stay a few minutes at 80, come up to 60 for a while, then 40 for a while, back down to 60, then up to 20 for a while….and your dive computer was with you and tracking (with its model) your on-gassing and off-gassing. Nice.

There are many dive computers using a number of different models, but they all work roughly the same and all track your movements up and down in the water. Consequently, with a dive computer you get longer dives than you can by assuming a square profile on a table, and you get shorter surface intervals before the next dive. Win-Win.

Today, dive tables are rarely taught in OW classes because they are tedious to use, and give considerably less information than your dive computer. However, many argue that dive tables help you to understand the on-gassing/off-gassing better, because they don’t bury everything into a small electronic device with just a (sometimes) complicated display on the front. True or not, they have pretty much gone away for recreational diving. Few know how to use dive tables, and they can easily be used incorrectly.

BUT, what happens if you are on a dive trip and your nice dive computer fails, perhaps during a dive? Best Practice, you immediately end the dive and surface, because you now do not know your depth nor how long you’ve been there, so you ascend and end the dive. Worse, you now do not know your nitrogen status…so if you want to do another dive you need to account for that residual nitrogen….and if you can’t do that, then you should stay out of the water for 24h to let your body “reset” to having completely off-gassed.

Is there anyway around being in the “penalty box” for a day? Yes, there are two ways, one is certain, one is problematic. Certain: carry a second dive computer with you on all dives, so it is a backup that knows your nitrogen status and can be used if your primary fails. Problematic: revert to dive tables. Attempt to work out a version of the dives so far today before your computer failed, and use the table to estimate your nitrogen status. Here is the problem with reverting to dive tables: suppose your computer failed on dive one of the day, and you had gone down to 80 ft for a while, then up to 60 to see the super-structure of a wreck, then up to 40 to spend some time on the reef, and were just getting ready to go to your safety stop about 50 minutes into the dive….and your computer failed. You can surface and end the dive (just don’t go up too quickly), but your square-profile equivalent dive for using tables is 80 ft for 50 minutes. But, the RDP table maxes out at 30 minutes at 80 ft. The dive you just did cannot be done on tables….the tables say you are in decompression status! THAT is the problem with trying to revert to tables,; maybe you can, but often you cannot.

And this is why tables are not taught any more in most OW classes. They do not suit the kind of diving that recreational divers do.

Yes, I am ‘Old School’ when it comes to Tables. My ‘Life’ situation up until 1989 was rather carefree and a dive computer was on my list. Well due to ‘Root Canals and crowns and interfering ( get this now) responsibilities, the dive computer got ‘Put on hold ‘ lots of times, so did the diving although I made efforts to stay in practice whenever I could find some water to dive in as charters and nice dive trips were out of the question. Things have changed now. I overhaul select vintage double-hose SCUBA equipment and make it safe to dive with again. Not a business, just a hobby which I like to share. News spreads…sometimes fast and one of my friends stepsons got a nice, older Oceanic regulator setup with Dacor OMNI dive computer, outdated, yes, but with a new battery, ‘Roared’ back to life. How much did I pay for this working regulator with octo, SPG, power inflator, and computer…nothing, nada, zilch, as the saying goes. I was most impressed as I read and reread the computer instructions as I can’t wait to actually get to try it out. Karma IS a wonderful thing. Now that my career is blooming and I am looking for an eventful, healthy retirement, I am wanting to hit the tropical dive sites and revisit all of my favorite haunts and discover some new ones.
giantfroginthepool
Scott G. Bonser

 

[scubadada]

Making your dives that are close to the NDL on your computer safer:

You can do the equivalent of a Shearwater adaptive safety stop using any computer. Simply extend your safety stop to 4, 5, or whatever minutes if you come within 5 or whatever you choose minutes of the NDL. I did this kind of safety stop for many years

The guesswork has been taken out. With the SurfGF function on Shearwater, Garmin, maybe other computers, you can simply sit at your safety stop until your SurfGF has decreased to a level consistent with what you want. I have not surfaced with a GF greater than the low 80s since purchasing my Teric in 2019. I certainly do not push my NDL on most dives and my average surfacing GF is around 50.

I do light deco on about 5% of my dives. I handle my 10 ft deco stop the same way. I extend my stop until SurfGF reflects the surfacing GF that I want.